Hospital Heating, Ventilation and Air Conditioning Systems
7.1.1 Purpose of Hospital Heating, Ventilation and Air Conditioning
The purpose of hospital heating, ventilation and air conditioning is to create a comfortable and healthy indoor environment while effectively preventing hospital-acquired infections, maintaining the most suitable medical and hygienic environment required during medical processes, implementing appropriate disaster prevention measures, and ensuring the safety, effectiveness and reliability of heating, ventilation and air conditioning equipment and systems. In addition, measures to prevent the spread of pollution and to save energy shall be taken on the premise of protecting the global environment.
Heating, ventilation and air conditioning often achieve their purposes through a single system, which is composed of a series of components and equipment. Among them, air conditioning involves the largest number of components and equipment, generally including cold and heat sources, air handling units, distribution equipment and automatic control. The vast majority of air conditioning systems have the following functions:
(1) Providing the required cooling and heating capacity.
(2) Relying on heating, refrigeration, ventilation and air conditioning equipment to heat, cool, humidify, dehumidify and remove contaminants from the supplied air, as well as to reduce noise.
(3) Distributing the conditioned air (containing sufficient fresh air) to each conditioned space and distributing it in an organized manner within the room.
(4) Controlling and maintaining indoor environmental parameters, such as air temperature, humidity, air quality, air movement, noise, and the pressure difference between the conditioned room and its surroundings, within preset ranges.
Heating is often described as supplying heat to a building in winter and maintaining a certain indoor temperature by means of indoor radiant or convective radiators. The main task of ventilation is to control harmful substances and excess heat and moisture in a space by means of supply air, exhaust air, or a combination of both, with the emphasis on safeguarding the health of indoor occupants. Air conditioning refers to simultaneously controlling multiple parameters and maintaining the indoor environment in a stable state. For example, the temperature, humidity, air movement, air quality, noise and pressure difference in a space are controlled within predetermined ranges, with emphasis on ensuring occupant comfort in the conditioned space or meeting the requirements of production processes.
7.1.2 Tasks and Requirements
(1) Air conditioning can usually be classified, according to user requirements, into comfort air conditioning and process air conditioning.
Comfort air conditioning provides occupants with a comfortable and healthy indoor environment suited to their work; for office buildings, the provided indoor environment is also required to help improve the work efficiency of indoor occupants.
Process air conditioning provides the special indoor environment required for product manufacturing, storage, or other research and development processes.
[Reference] Hospitals have many internal departments, and the functions and requirements of each department differ. Generally speaking, a general hospital can be divided into three major departments: the outpatient department, the inpatient department, and the diagnosis and treatment department.
The outpatient department is where the vast majority of patients are diagnosed, treated or admitted; it has a large flow of people and a wide variety of diseases, and patients with different diseases are mixed together. The inpatient department is a place for patients' treatment and rehabilitation, and also a place where patients live. Except for special areas such as clean operating rooms, aseptic wards and intensive care units, generally speaking, the outpatient and inpatient departments require comfort air conditioning.
The diagnosis and treatment department is the diagnostic and therapeutic center of the whole hospital, as well as the supply center for equipment, medical instruments and pharmaceuticals. It is the department with the most advanced equipment and the most complex functions in the hospital. It includes physiotherapy, radiology, laboratory testing, functional diagnosis, isotope rooms, etc., and also includes central sterilization, instrument and dressing supply, pharmaceutical preparation and dispensing, drug distribution, etc. Most indoor environmental control is determined by equipment and process requirements. Likewise, the indoor environmental control of places such as clean operating rooms, aseptic wards and intensive care units is determined by medical process requirements; therefore, most departments of the diagnosis and treatment department can be classified under process air conditioning.
(2) Tasks of hospital HVAC.
1) Create a comfortable and healthy environment capable of supplying fresh and clean air to patients and medical staff, and control indoor parameters such as temperature, humidity and air movement so that people feel pleasant and at ease. 2) Creating environments that promote medical effectiveness—for example, keeping newborn infants warm, controlling high-temperature environments to raise patients' metabolism or low-temperature environments to suppress patients' metabolism during surgery, maintaining high-humidity wards for patients with respiratory diseases such as asthma, and providing an effective environment for moisture metabolism in the open therapy of patients with burns over the whole body—all of these are beneficial to treatment.
3) Creating environments that ensure the normal operation of medical equipment, such as X-ray computed tomography scanners (CT scanners for short), electron accelerators, and magnetic resonance imaging machines (MRI machines for short). To maintain and bring their functions into full play, the requirements on the indoor environment are very high. In addition to the main diagnostic or treatment rooms, these devices also involve large machine rooms, computer rooms, and a series of auxiliary rooms. Machine rooms, computer rooms, or diagnostic and treatment rooms often have special requirements for indoor parameters, and the various auxiliary rooms also have different requirements. Large computer centers used for modern hospital management also have certain requirements for the indoor environment.
7.1.3 Selection of System Types and Design Principles
(1) HVAC systems.
System types can be classified, according to the medium circulating in the system, into all-water, steam, all-air, air-water, refrigerant, and other systems. Specifically, an appropriate HVAC system should be selected by considering many aspects, such as the use and nature of the building, the characteristics of the thermal and humidity loads, the control parameters and their precision, the area and location of the air-conditioning machine room, and the initial investment and operation and maintenance costs.
All-air systems All loads of the room are borne by centrally treated air.
All-air systems can be further divided, according to whether the supply air volume varies, into:
1) Constant air volume systems. The supply air state varies with changes in the indoor thermal and humidity load, while the air volume supplied to the room remains constant. When the thermal and humidity load is large, the supply air temperature difference is large; when the thermal and humidity load is small, the supply air temperature difference is small.
2) Variable air volume systems. The air volume varies with changes in the indoor thermal and humidity load, while the supply air state remains basically unchanged. When the thermal and humidity load is large, a larger air volume is supplied; when the thermal and humidity load is small, a smaller air volume is supplied.
Air-water systems Part of the air-conditioning load is borne by centrally treated air, while the remaining loads are handled by water as the medium delivered into devices within the air-conditioned room, where the indoor air is treated locally (heating, cooling, etc.). Air-water systems include systems combining outdoor air with fan coil units, displacement ventilation combined with radiant ceilings, and the like.
All-water systems All room loads are borne by centrally supplied chilled or hot water, such as fan coil systems, chilled (hot) radiant panel systems, and hot water heating systems.
Refrigerant and steam systems The cooling and heating loads required indoors are supplied entirely by the refrigerant evaporating and condensing within the room. According to the cooling method of the outdoor condenser in summer, they can be classified into air-cooled, water-cooled, and other types; according to installation and combination, they can be classified into window type, vertical cabinet type (the refrigeration unit and air-conditioning equipment assembled in the same vertical cabinet), and split type (generally the compressor and condenser form the outdoor unit while the evaporator is the indoor unit, as well as inverter-controlled multi-split units), etc. Steam heating systems, which in winter utilize the condensation of steam and release of heat in indoor heat-dissipating equipment (unit heaters, radiators), also belong to this category. Steam heating systems can be further divided into low-pressure steam heating and high-pressure steam heating systems.
【Reference】 All-air constant air volume systems can be divided, according to how the return air is utilized, into once-through systems (100% outdoor air systems), primary return air systems, and primary and secondary return air systems. Mixing outdoor air with indoor return air is usually called primary return air, while mixing indoor return air with air that has undergone thermal and humidity treatment is called secondary return air.
All-outdoor-air systems are used only when the exhaust air volume of the rooms in the system is greater than the supply air volume calculated from the load, and in cases where the rooms in the system contain hazardous substances or harmful gases, or where the process has specific requirements and air recirculation is not allowed. When the air-conditioned room allows a larger supply air temperature difference or the indoor moisture gain is large, a primary return air system should be adopted. When the air-conditioned room requires a smaller supply air temperature difference, or the indoor moisture gain is small and the allowable fluctuation range of relative humidity is large, a secondary return air system is preferable.
Since once-through systems (100% outdoor air systems) consume too much energy, return air should be utilized as much as possible on the premise of ensuring the required outdoor air volume.
【Reference】 According to the arrangement of HVAC system equipment, systems are classified into centralized, decentralized (local), and semi-centralized (hybrid) systems. [Reference] As for which type of air conditioning is most suitable for hospital buildings, no generalization can be made. Since the various departments of a hospital building differ in function and in their requirements for air conditioning, it is impossible to select a single uniform type; an appropriate system may be chosen with reference to Table 7.1. Compared with other buildings, hospital air conditioning systems are complex and involve numerous methods, presenting greater difficulties in design, construction, and management.
Table 7.1 Comparison of HVAC Systems
| Item | Centralized HVAC system | Semi-centralized HVAC system | Fully decentralized HVAC system |
|---|---|---|---|
| Nature of space or production process | High coefficient of simultaneous use among rooms; medical or production processes are continuous; suitable for large-scale production processes | Each room has a certain degree of independence; medical or production processes can be continuous; cross-contamination between rooms can be avoided | Each room is independent, with a single medical or production process; suitable for renovation projects |
| Space characteristics | Rooms are relatively large in area and numerous, centrally located, but the temperature, humidity, cleanliness, or degree of sterility of the rooms should not differ too much | Rooms are centrally located, and different rooms can be combined into one system | Single rooms or rooms dispersed in location |
| Equipment cost per unit area | Relatively low | Depends on the price of terminal units; the cost lies between the two | Relatively high |
| Maintenance and operation | Requires specially trained operators, but the maintenance workload is small; system management is relatively complex, and individual rooms cannot make their own adjustments | Between the centralized and fully decentralized types; each room can adjust on its own, and management is convenient | Simple to operate; occupants can operate it themselves, but the maintenance workload is relatively large; adjustment and management are simple |
(2) Design principles for hospital air conditioning systems.
1) Reasonable zoning of air conditioning. The air conditioning system should be zoned with care. First, a detailed investigation and repeated comparison must be carried out with respect to the functions of the various departments and rooms of the hospital, the indoor air conditioning design parameters, the equipment situation, hygiene requirements, hours of use, and air conditioning loads; only then can the system be zoned reasonably, so as to ensure the parameters required by each room, reduce adverse influences between different zones, facilitate management and maintenance, and lower operating costs. Generally speaking, rooms with high cleanliness requirements, severely contaminated rooms, or independent, self-contained areas are best made into separate systems.
2) Appropriate air conditioning methods. Besides ensuring the special temperature, humidity, and cleanliness required by each room, the choice of hospital air conditioning method also affects the initial investment of the system, operating costs, indoor noise and vibration, and the capacity to remove contamination. In selecting the air conditioning method, particular emphasis should also be placed on ease of use, low maintenance requirements, and high reliability, especially for operating rooms, neonatal rooms, intensive care units, and the like. Given the relatively weak air conditioning management and maintenance capabilities in domestic hospitals, if the HVAC system or its operation and control modes are too complex, the results envisioned in the design can often not be achieved.
3) The system should be flexible and have reserve capacity. The flexibility of the system is mainly reflected in its ability to adapt to the development of medical technology and the updating of diagnostic and treatment equipment. Emphasizing the flexibility of the system (including the cooling and heating sources) and leaving reserve capacity is intended to accommodate changes in the floor plan of the hospital building, changes in indoor loads, and the needs of building renovation or expansion.
4) High requirements for noise attenuation and vibration reduction. Most hospital departments have high requirements for noise attenuation and vibration reduction; otherwise, patients' recovery will be hindered, the normal medical work of healthcare personnel will be disturbed, and some precision diagnostic and treatment equipment may even be affected. Noise attenuation and vibration reduction must be considered comprehensively, taking into account system zoning, the choice of system type, equipment selection, and the location of equipment rooms.
5) The system should incorporate energy-saving measures. The coefficient of simultaneous use of hospital air conditioning is relatively low: some departments, such as wards, need to operate around the clock; some, such as operating rooms, need to run only for short periods; and some, such as emergency treatment rooms, need to be able to run at any time, resulting in a large difference between peak and valley loads. Some departments require heating or air conditioning to be started in advance and shut down with a delay, which adds complexity to the seasonal changeover of the system. Generally speaking, hospital air conditioning requires a large amount of fresh air, and some departments even require 100% fresh air. All of this calls for corresponding energy-saving measures to be considered in the system design.
6) Appropriate system size. The functions of the various departments in a hospital building differ greatly, and their operating hours also vary. Therefore, the air conditioning system should not be too large or too centralized, but it is also unnecessary to adopt decentralized systems excessively. Generally, it is advisable to adopt centralized supply of cooling and heating sources, with zoned distri ...system is preferable. In hospitals in China, except for wards and the like, the air conditioning is shut down at night. Attention should be paid to the principle that each air-conditioned zone should be able to be sealed off from the others; otherwise, cross-infection can easily be caused by uncontrolled air movement through ducts, stairwells, or between zones.
[Reference] In hospitals, the medical processes and medical activities, as well as the medical staff and patients, continuously generate harmful substances that pollute the indoor air and cause it to fall short of the hygienic standards. The most effective way to prevent harmful substances from polluting the indoor air is to capture them directly at the points where they are generated and, after purification, discharge them outdoors; this ventilation method is called local exhaust ventilation. A local exhaust ventilation system requires a small air volume and achieves good results, so it should be given priority in design.
A local exhaust ventilation system generally consists of local exhaust hoods, air ducts, purification equipment, fans, etc.
[Reference] If, due to limitations of medical conditions, unfixed or dispersed sources of harmful substances, or other reasons, local exhaust ventilation cannot be adopted, or if after adopting local exhaust ventilation the indoor concentration of harmful substances still exceeds the hygienic standards, then it is necessary to ventilate the entire space, that is, to supply a large amount of fresh air to dilute the concentration of harmful substances in the whole area below the maximum allowable concentration; this method is called general ventilation. It should be pointed out that the effectiveness of general ventilation is related not only to the ventilation rate but also to the organization of the ventilation airflow. This requires correctly selecting an appropriate ventilation method, and rationally arranging the positions of the supply and exhaust outlets, distributing the air volumes, and selecting the outlet types, so as to achieve better results with a smaller ventilation volume.
[Reference] The three methods commonly used for general ventilation are as follows:
① Dilution ventilation. This is the most commonly used method, also known as mixed ventilation. The clean supply airflow is distributed turbulently in the room, continuously diffusing and mixing within the room, diluting the harmful substances in the indoor air and reducing their concentration, while at the same time continuously discharging the polluted air outdoors, so that the concentration of harmful substances in the indoor air does not exceed the maximum allowable limit specified by the hygienic standards.
To determine the dilution ventilation rate, the calculation is first based on an ideal situation, namely, it is assumed that the harmful substances are emitted uniformly in the room (the concentration distribution of the harmful substances in the indoor air is uniform), that the mixing between the supply airflow and the indoor air is completed instantaneously, and that the supply and exhaust airflows are isothermal. Therefore, based on the mass balance, the dilution ventilation rate required for the indoor harmful substance concentration to reach $y_2$ at steady state can be calculated by the following formula:
$$L = frac{x}{y_2 - y_0} (mathrm{m^3/s}) tag{7.1}$$
where: $L$ — dilution ventilation rate ($mathrm{m^3/s}$);
$x$ — emission rate of harmful substances (g/s);
$y_0$ — concentration of harmful substances in the supply air ($mathrm{g/m^3}$);
$y_2$ — concentration of harmful substances in the indoor air ($mathrm{g/m^3}$), determined according to the hygienic standards.
In reality, the distribution of the harmful substances in the room and the ventilation airflow can never be very uniform, nor can the mixing process be completed instantaneously. Even if the average indoor concentration of harmful substances complies with the hygienic standards, the concentration of harmful substances in the air near the sources may still be much higher than the indoor average. In order to ensure that the concentration of harmful substances in the breathing zone of people near the sources is kept below the allowable value, the dilution ventilation rate actually required is much larger than the value calculated by formula (7.1). Therefore, a safety factor $K$ is introduced into formula (7.1), so that it becomes
$$L = frac{Kx}{y_2 - y_0} (mathrm{m^3/s}) tag{7.2}$$
The determination of the safety factor $K$ must take many factors into consideration, such as the toxicity of the harmful substances, the distribution of the sources and the non-uniformity of their emission, the indoor airflow organization, and the effectiveness of the ventilation; in general, it can be selected empirically within the range of 3–10.
② Displacement ventilation, also called thermal displacement ventilation. The supply air outlets are often installed in the lower part of the room, and the return air outlets in the upper part. Slightly cool air is supplied at a low velocity ($V<0.2sim0.3$m/s); due to the density difference from the indoor air, it sinks and diffuses slowly, forming a layer of "fresh air shallow pool" in the lower part of the whole room. Where there is surplus heat (such as people, equipment, etc.) has a positive temperature gradient in the vertical direction. The fresh air supplied at the lower part, with relatively small disturbance, first passes through the working zone under the action of thermal buoyancy, flows over the heat sources (such as occupants, equipment, etc.), entrains the surrounding hot air, and its temperature rises; driven by the "push" of the subsequent supply air, it rises directionally toward the return air outlet where it is "sucked" out, forming an approximately displacement airflow in the room. The polluted air in the working zone is continuously replaced by slightly cooler fresh air until a steady state is reached. The occupants in the room are always surrounded by the fresh supply airflow. Due to the restriction of the ceiling, a concentration stratification will form in the room: the upper part of the room has a higher pollutant concentration and is more thoroughly mixed, while the lower part is relatively clean and stagnant, thereby ensuring indoor air quality. It can be seen that the supply air volume it requires is smaller than that of dilution ventilation. Displacement ventilation is generally suitable for occasions where pollution sources are accompanied by heat sources, with a room height of not less than 2.4m.
③ Unidirectional airflow ventilation (Unidirectional airflow ventilation). Also called extrusion ventilation; unidirectional flow is sometimes called piston flow. The clean supply air forms, across the entire cross-section of the room (which can be vertical or horizontal), an airflow with parallel streamlines, a single flow direction, and uniform velocity, like a large piston pushing the entire polluted indoor air out. Once pollutants are generated in the room, they will be removed by the shortest route and will not spread. This ventilation form requires the largest air volume and achieves the best effect. However, it has a high construction cost and large operating expenses, and can only be used in places requiring high cleanliness. Its supply air volume is determined by the following formula:
$$L = v cdot S , (mathrm{m^3/s}) tag{7.3}$$
where: $L$——supply air volume ($mathrm{m^3/s}$); $v$——average air velocity at the cross-section ($mathrm{m/s}$); $S$——cross-sectional area of the room ($mathrm{m^2}$).
According to the dominant airflow pattern in the room, the above airflows can be divided into two major types. Traditional dilution ventilation and unidirectional airflow ventilation are fluid-dynamically controlled air distribution, while thermal displacement ventilation is a thermally controlled indoor air distribution. Ideal dilution ventilation achieves a uniform concentration everywhere in the room, with the exhaust air concentration equal to the concentration in the indoor working zone. The exhaust air concentrations of unidirectional airflow ventilation and displacement ventilation are much higher than the concentration in the indoor working zone, which shows that their ventilation effectiveness is better than that of dilution ventilation. Unidirectional flow is also often used in highly clean and sterile rooms.
【Reference】Radiant cooling is a new type of air conditioning method that has emerged from Europe in recent years. A better approach is to use displacement ventilation in combination with a cooled ceiling. The cooling ceiling panel and the water pipes can be made as an integral unit, directly forming a ceiling panel unit; or the water pipes and the metal ceiling panel can be connected through fins to form a unit; the water pipes can also be embedded in the ceiling panel in the form of capillary tubes, assembled into an installation unit. The cooling ceiling can only remove the sensible heat load and cannot remove the moisture load. To avoid condensation on the ceiling panel, the supply water temperature should be higher than the dew point temperature of the indoor air, usually above 14℃.
When the cooling load is large, the displacement ventilation system must at least remove the indoor moisture load, and the cooling capacity of the cooled ceiling should be controlled at 50%～60% of the total cooling capacity to ensure the normal operation of the displacement ventilation system. Displacement ventilation is also conducive to removing indoor harmful substances and does not cause cross-infection, so it is very suitable for use in hospital wards, but it is expensive.
Commonly used cold sources include the following:
- Since floor cooling uses chilled water at about 17℃, where well water or groundwater is available, the cost is particularly low.
- Heat pumps: since they can both cool and heat, they are especially suitable for floor cooling and heating systems and are reliable in operation; air/water heat pumps are mostly used, and water/water heat pumps are sometimes used as well.
- Water at a suitable temperature produced in technological processes.
【Reference】If a floor cooling system is used in summer while heating is also needed in winter, adopting a low-temperature radiant floor is a good method. It uses the interior floor of the building for heat exchange. It is generally believed that the chilled water temperature for floor cooling should be controlled at 16～18℃; if the water temperature is too low, condensation will occur on the floor and the feet will feel uncomfortable. To ensure human comfort, the floor surface temperature should preferably be higher than 18℃. Under this condition, depending on the ambient temperature, the room temperature can be lowered by 3～5℃. In relatively dry regions, the water temperature can even be lowered to 13℃ without causing condensation, in which case the cooling effect is greatly enhanced. The floor surface temperature is affected by the outdoor temperature and the degree of thermal insulation of the building envelope, This should be fully considered. For example, under high load conditions, when the wall surface temperature reaches 30℃, even if the inlet water temperature is as low as 10℃, the floor temperature rarely falls below 20℃, so condensation will not occur.
During winter heating, this system uses low-temperature hot water flowing through the entire floor as the heat-dissipating surface. While the floor heats the surrounding air through convective heat transfer, it also exchanges heat by radiation with the surrounding envelope structures, thereby raising the surface temperature of the envelope; the radiant heat transfer accounts for approximately 50% of the total heat transfer. Besides advantages such as saving the effective area of rooms and facilitating interior decoration and furnishing, the most outstanding features of floor heating are its comfort and energy efficiency. Radiant heating can reduce the radiant heat dissipation from the human body caused by the low temperature of the inner surfaces of the envelope, thus enhancing human comfort. When radiant heating is used, since the indoor air flow is weak, the convective heat transfer coefficient between the inner surfaces of the envelope and the indoor air is greatly reduced, so the building heat loss is considerably decreased. At present, its cost is still relatively high, and it is only used for heating open spaces in hospitals (such as nurses' stations) or other places requiring a high degree of comfort.
7.1.4 Hospital Cooling and Heating Sources
Heat sources are generally steam boilers and hot water boilers, with fuels including coal, oil, and gas; high-pressure steam or high-temperature water supplied by thermal power stations may also be used. Cooling sources include the electric compression type and the absorption type, which are often made in unit form to directly supply cooling media (such as air, water, refrigerants, etc.). The electric compression type can be divided into reciprocating, screw, and centrifugal types, and can also be classified into cooling-only and heat pump types; the absorption type includes single-effect, double-effect, and even triple-effect units, as well as direct-fired cold/hot water generators. Their capacities and performance are shown in Table 7.2.
Table 7.2 Capacity Range and Performance of Refrigerating Machines
| Type | Capacity/kW | Energy efficiency ratio COP (primary energy) | Energy efficiency ratio COP (secondary energy) | |
|---|---|---|---|---|
| Electric compression | Reciprocating | 70～140 | 3.2 | 1.12 |
| Electric compression | Screw | 75～1 800 | 3.3 | 1.16 |
| Electric compression | Centrifugal | 350～1 800 | 3.5 | 1.26 |
| Absorption | Single-effect | 350～3 500 | 0.58 | 0.50 |
| Absorption | Double-effect | 350～3 500 | 1.30 | 1.11 |
| Absorption | Direct-fired cold/hot water generator | 350～3 500 | 0.97 | 0.82 |
Note: The inlet/outlet chilled water temperature of electric compression refrigerating machines is 7℃/12℃, and the inlet/outlet water temperature of absorption refrigerating machines is 8℃/13℃.
[Reference] COP (Coefficient of Performance) in the table is called the performance parameter of a refrigerating machine; it is the ratio between the input work (compressor) and the output work (refrigeration capacity) of the refrigerating machine (or heat pump). In the United States, it is called the energy efficiency ratio EER(Energy efficiency ratio), and the EER over a period of time is called the seasonal energy efficiency ratio (SEER).
[Reference] The selection of cooling and heating sources in the early stage of hospital construction is very important, and should be based on the basic national policy of rationally utilizing energy, improving energy utilization efficiency, and conserving energy. Good cooling and heating source equipment and their combinations must also be capable of reducing environmental load and possess reliability, safety, and economy, as well as convenience in maintenance and management and high performance in upgrading. Since the energy structure and prices vary from region to region and economic strength differs considerably, the selection is also subject to constraints from many aspects such as environmental protection and fire protection. Moreover, all these factors are constantly changing, so it is very difficult to obtain a fixed and most reasonable combination scheme of cooling and heating sources. At present, there are the following cooling and heating source combination schemes and the corresponding selection principles (Table 7.3). Table 7.3 Heat (Cooling) Source Systems for Air Conditioning
| Method | Cooling and Heating Source Combination | Selection Principles |
|---|---|---|
| Conventional method | Electric compression refrigeration machine and (coal-fired, oil-fired, gas-fired) boiler; electric compression refrigeration machine and municipal (or district) heating | When the local power supply is not tight, electric compression refrigeration machines are preferred; large systems mainly use centrifugal units, medium-sized systems mainly use screw units, and small systems mainly use reciprocating units; where conditions permit, centralized heating or oil-fired and gas-fired boilers are preferred |
| Lithium bromide absorption refrigeration machine | Single-effect absorption type and boiler; double-effect absorption type and boiler | Preferred when the power supply is tight and there is heat supply from a thermal power station or sufficient boilers for winter heating, especially when waste heat or surplus heat is available for utilization |
| Lithium bromide absorption refrigeration machine | Direct-fired chilled/hot water generator | Preferred when the power supply is tight and cheap gas is available in summer |
| Heat pump method | Water heat source | Buildings with internal and perimeter zones requiring simultaneous cooling and heating, or where clean water sources are available |
| Heat pump method | Air heat source | Small and medium-sized buildings requiring year-round air conditioning, or where the use of primary energy is inconvenient |
| Heat pump method | Soil heat source | Regions with good geothermal conditions |
| Heat pump method | Heat recovery | Preferred in situations where waste heat or surplus heat is available |
| Special method | Total energy method | Actively develop combined heat, power and cooling cogeneration technology where conditions permit |
| Special method | District cooling and heating | Actively develop district cooling and heating stations where conditions permit |
| Special method | Cool (heat) storage method | To balance the peak-valley difference in power supply, systems combining thermal storage air conditioning with low-temperature air distribution can be promoted; if there is a substantial preferential electricity tariff, small systems may also adopt electric boilers that store heat using off-peak electricity |
[Reference] Generally speaking, the investment in cooling and heating sources and their operating energy consumption account for about 30% of an entire air conditioning system, so the selection of units is of great importance. According to Clause 4.8 of the national standard Economic Operation of Air Conditioning Systems, refrigeration units with a high coefficient of performance (COP) should be given priority. Generally, the selection of chillers is determined based on the calculated load, and no additional selection factor should be applied.
[Reference] In China, especially in the south, heat pumps are increasingly used directly as the cooling and heating source for indoor environmental control. Classified by heat source, there are water-source, air-source and soil-source types.
A heat pump is defined as a device that absorbs heat from a heat source at a lower temperature and transfers it to a heat source at a higher temperature. It can be seen that all refrigeration equipment, including air conditioners and refrigerating machines operating on refrigeration cycles, are heat pumps. However, in engineering practice, the term heat pump usually refers to systems with heating as their purpose; there are heat pumps that provide both heating and cooling, as well as heating-only heat pumps or heat recovery heat pumps that provide heating and cooling simultaneously.
The heating cycle of a heat pump is the same as the refrigeration cycle, except that it can, as required, control the supply of heat to the air-conditioned room through its condenser or the supply of cooling through its evaporator; sometimes both heating and cooling are utilized.
① For air conditioning systems, it is particularly important to select the commonly used air-source heat pump type chilled (hot) water units with a high coefficient of performance (COP). The heating capacity of a heat pump should be consistent with the heating load of the building. Since the outdoor air temperature and humidity vary greatly with region, season, and time of day, these variations have a significant impact on the design, selection and operation of air-source heat pumps. The main problem with air-source heat pumps is that as the outdoor air temperature decreases, the evaporation temperature drops, the heat pump efficiency decreases and the heating capacity declines, while the building's heat demand increases. Especially when the air temperature drops below －5℃, the heating capacity drops sharply, resulting in an imbalance between supply and demand. As the ambient temperature changes, there is excess or insufficient heating capacity during most of the time.
② The rapid development of lithium bromide absorption refrigeration units, especially direct-fired units, has provided more flexible options for the selection of cooling and heating sources. Its most notable feature is low electricity consumption; for example, the power consumption of the direct-fired lithium bromide absorption chilled/hot water unit itself is only 3%～4% of that of a centrifugal chiller, and even when auxiliary equipment is taken into account, the power consumption is only about 23%. Therefore, when the power supply is tight, or when hospitals and heat networks have cheap steam or high-temperature hot water supply, or when other surplus heat is available, selecting a lithium bromide absorption refrigeration machine may be a better solution. However, the energy utilization efficiency of lithium bromide absorption refrigeration units is lower than that of electric compression chillers.
[Reference] Lithium bromide absorption refrigeration machines should be rationally determined according to the heat source (or fuel) conditions available to the user; according to Table
7.4 Selecting Unit Types Based on Heat Source Parameters.
Table 7.4 Heat Source Parameters of Various Unit Types under Nominal Conditions
| Unit Type | Heat Source (or Fuel) Type and Parameters |
|---|---|
| Direct-fired unit | Natural gas, city gas, light oil |
| Steam double-effect unit | Rated steam pressure of 0.25, 0.4, 0.6, 0.8 (MPa) |
| Hot water double-effect unit | Hot water ＞150℃ |
| Steam single-effect unit | Waste gas (0.1MPa) |
| Hot water single-effect unit | Waste heat (80～150℃ hot water) |
【Reference】The standard configuration of a direct-fired lithium bromide absorption unit provides a heating capacity of 80% of its cooling capacity, which is a relatively economical and reasonable configuration. Therefore, when selecting a direct-fired lithium bromide unit, consideration should be given to matching the building's cooling and heating loads with the unit's cooling and heating capacities. When the heating load exceeds the unit's heating capacity, the heating capacity should not be increased by upsizing the unit type; otherwise, investment will increase and unit efficiency will decrease. The high-pressure generator or burner may be appropriately enlarged, but if enlarged too much, it will also affect the matching between the high- and low-pressure generators, likewise causing reduced efficiency and increased energy consumption.
Most hospitals in China have built central boiler rooms as heat sources, all using steam boilers. The number of boilers should preferably be 2 or more to ensure the hospital's steam supply. In addition to supplying steam for the whole hospital, steam boilers can also supply heating hot water and domestic hot water to the hospital through steam-water heat exchangers in the heat exchange station. Generally speaking, the peak hours of hospital steam use and the peak hours of hospital heating are staggered during the day, so the surplus steam can be used to produce heating hot water and domestic hot water through heat exchangers. Boiler selection can be based on local fuel supply conditions, choosing coal-fired, oil-fired, or gas-fired boilers, or electric heating boilers.
However, hospitals consume a large amount of hot water, so the boiler room should preferably install both steam boilers and hot water boilers. The fuel of the hot water boilers should preferably be the same as that of the steam boilers, which offers flexibility in use, lower operating costs than producing hot water via steam-water heat exchange, and greatly reduced transmission energy consumption.
【Reference】Air-conditioning systems heated by urban heat networks or regional boiler room heat sources (steam, hot water) should be equipped with heat exchangers for heat supply. Heat exchangers should be of new types that are highly efficient, compact in structure, easy to maintain, and have long service lives. The capacity of the heat exchangers should be determined according to the calculated heating load. When the primary heat source has poor stability, the heat transfer surface area of the heat exchanger should be multiplied by a factor of 1.1～1.2. The steam condensate of steam-water heat exchangers should generally be recovered and reused. Heat exchangers should be equipped with automatic temperature control devices.
【Reference】In recent years, out of concern for protecting the urban environment, many large cities have banned coal burning and vigorously promoted clean energy such as natural gas (and even electricity). In the past, hospitals adopted central boiler rooms to centrally supply steam for heating, an approach based entirely on the coal-fired boiler model, originally intended to improve coal-fired boiler efficiency and reduce pollutant emissions. For natural gas (or electricity), pollution is no longer an issue, and the efficiency difference between large and small boilers is no longer significant. Since the hospital's gas pipe network (or power grid) has already reached every department, there is no need to invest heavily in building a heat network; small-capacity hot water boilers (or so-called large water heaters) can be installed on site. These have almost no special requirements for installation locations, and operation and management are very simple. This decentralized, independent heating can easily achieve reasonable zoning and piping, and can greatly shorten transmission distances; each department can switch boilers on and off at any time as needed, and the problems of different departments starting up early and shutting down late are thus readily solved. Since end users can use heat sources more conveniently and effectively, the design and management difficulties of the past central heating network—such as zoned heating, advance heating, and emergency heating—are resolved, and at the same time the "dripping, escaping, and leaking" of steam transmission pipelines is also eliminated, greatly reducing heat transmission losses.
7.1.5 Machine Room Setup and Requirements
(1) Hospitals should generally adopt centralized cooling and heating supply systems. When selecting chillers, there should generally be no fewer than 2 units; when only 1 unit is needed, a multi-compressor type with joint control should be selected. The number of chillers should not be excessive and should be compatible with the variation patterns of the air-conditioning load and the regulation requirements. Decentralized air-cooled or water-cooled packaged or split air-conditioning units should only be adopted when the following conditions are met.
1) Buildings where the air-conditioned area is relatively small, where a centralized cooling and heating supply system is uneconomical, or where machine rooms and piping cannot be arranged. 2) Buildings in which the rooms requiring air conditioning are too scattered in layout.
3) In buildings with centralized cooling and heating systems, the few rooms whose hours of use and usage requirements differ.
4) Rooms with special requirements for temperature and humidity.
(2) The following points should be noted in the selection of air conditioning units and the arrangement of machine rooms in hospitals.
1) The location of the machine room and the placement of the units should take into account factors such as routine inspection, maintenance, and replacement of the units.
2) Air conditioning units capable of effectively preventing secondary contamination should be selected. The coils, drain pans, humidifiers, etc. in air conditioning units and fan coil units must be easy to clean and disinfect.
3) To facilitate maintenance of the air conditioning units or replacement of the filters inside them, it is desirable to install the air conditioning units in the machine room or in a technical interlayer. For the convenience of operation and maintenance management, they should not be installed inside the ceiling.
4) The area of the air conditioning machine room and the size of the space between the air conditioning unit and the various pipe fittings should be determined so that filters, valves, etc. can be operated conveniently and maintained easily.
[Reference] In large and medium-sized machine rooms, the main machine room and the pump room should preferably be set up separately, and a control room (with observation windows or glass partitions) and a maintenance room should be provided, with air conditioning terminal units installed in the rooms. The machine room should be provided with water supply and drainage facilities, and the floor and equipment bases should be finished with materials that are easy to clean. The machine room should have good ventilation facilities. Machine rooms on basement levels should be provided with mechanical ventilation, with the number of air changes not less than 6 times/h.
[Reference] The equipment in the machine room should be arranged compactly, with rational piping flow, convenient operation, and appropriate maintenance space, and should comply with the following requirements:
① The clear distance between a unit and the wall should not be less than 1.0m, and the distance from the power distribution cabinet should not be less than 1.5m.
② The clear distance between units, or between a unit and other equipment, should not be less than 1.2m.
③ A maintenance distance not less than the length of the evaporator, condenser, or low-temperature generator should be provided.
④ The clear distance between the unit and the pipes, flue pipes, or cable trays above it should not be less than 1.0m.
⑤ The width of the main passages in the machine room should not be less than 1.5m.
[Reference] In the design of a direct-fired absorption machine room, the design of the oil storage tanks and day oil tanks, the oil (gas) supply system, and the flue gas exhaust system should comply with the relevant provisions of the current national standards.
7.1.6 Calculation of Air Conditioning Loads and Supply Air Volume
(1) The heat and moisture disturbances to the indoor environment come from two sources: one is from nature; the other is from production processes and human activities. On the natural side, variations in outdoor atmospheric temperature and humidity and the strength of solar radiation heat affect the indoor environmental parameters through the building envelope and the incoming air; on the indoor side, heat or moisture is released during process operations and the running of production equipment, and even in civil buildings, human bodies, lighting, equipment, appliances, etc. also generate heat or moisture — all of these affect the indoor environmental parameters. The surplus heat and surplus moisture generally also vary with changes in indoor and outdoor conditions; from these, the surplus heat and surplus moisture that have the greatest influence, or that frequently affect the indoor balance, should be determined as the "load" quantities for air conditioning calculations; sometimes the indoor surplus heat in summer is called the "indoor cooling load," and the surplus heat in winter is called the "indoor heating load." The magnitude of the heat and moisture loads has a decisive influence on the equipment and scale of the air conditioning system, and also concerns the rationality and economy of the air conditioning system. Therefore, reasonable measures should be considered jointly from the aspects of architecture, process, etc. to reduce the load.
In addition to the above room loads (loads occurring within the air-conditioned rooms), system loads (loads occurring outside the air-conditioned rooms) also constitute air conditioning loads. For example, the fresh air load caused by the fresh air state differing from the indoor air state, and the loads caused by heat transfer through air ducts and heat generated by fans, do not act directly on the indoor space, but ultimately they are also borne by the air conditioning system. Therefore, air handling equipment must also be selected according to the system load.
The load of a clean operating room has the characteristics of a biological cleanroom. Medical equipment in the operating room should not be regarded as a stable, continuous heat (cooling) load, which would make the load estimate for the operating room too high.
At present, most operating rooms are airtight small chambers set within civil construction envelope structures, with various pipes running through the intervening passages between the chambers. If With a double-corridor or similar floor plan, the operating room is located in the interior zone. The proportion of the air-conditioning load attributable to the building envelope is even smaller, and the load calculation can be entirely treated as steady-state heat transfer. Before surgery there is almost no moisture load in the room; during surgery, personnel gather around the operating table, so moisture generation is concentrated. Moreover, although there are now more and more medical devices in the room, few are used continuously throughout the operation, and the simultaneous use factor is also small—this holds even for deep surgeries such as cardiac surgery. Furthermore, among newly developed devices, special-purpose ones predominate while general-purpose ones are few. For routine operations, the commonly used medical equipment consists of only a few items such as electrosurgical units and anesthesia machines. Relatively speaking, lighting heat gain and personnel heat and moisture generation vary little. In other words, the load characteristics during surgery are that the heat load varies considerably while the moisture load is relatively stable, which causes large variations in the indoor heat-moisture ratio—this is the main cause of indoor relative humidity exceeding the specified limit. Therefore, the cooling capacity of the operating room air-conditioning system can be sized according to the peak heat (cooling) load, but the system configuration needs to give greater consideration to variations in the heat-moisture ratio; directly applying industrial constant temperature and humidity units is also inappropriate.
(2) The capacity and equipment of the air-conditioning system. These are generally determined based on the summer cooling load. Because the heat and moisture disturbances to the air-conditioned room differ between winter and summer, with the degree of impact in summer being greater than in winter, and because the measures and devices for cooling and dehumidifying air are more complex than those for heating and humidifying air, and the equipment investment and operating costs are also greater in summer than in winter, the supply air volume and equipment capacity are usually determined according to the summer load. Except for rooms requiring year-round air conditioning, in southern China air conditioning is mostly used during the hot season. Even in cold regions where heating is required, the interiors of some buildings are still heated by heating equipment in winter, and air conditioning is used only in summer.
[Reference] The summer calculated heat gains and moisture gains of an air-conditioned room or area shall be determined according to the items in Table 7.5:
Table 7.5 Summer Calculated Heat Gains and Moisture Gains
| No. | Summer calculated heat gain of the air-conditioned room or area | Summer calculated moisture gain of the air-conditioned room or area |
|---|---|---|
| 1 | Heat transferred through the building envelope | Moisture gain through the building envelope |
| 2 | Heat dissipated by the human body | Moisture dissipated by the human body |
| 3 | Heat brought in by infiltrated air | Moisture brought in by infiltrated air |
| 4 | Heat dissipated by food or materials | Moisture dissipated by food or materials |
| 5 | Heat dissipated by equipment, appliances, piping, and other internal heat sources | Moisture dissipated by equipment |
| 6 | Solar radiant heat entering through exterior windows | Moisture dissipated in chemical reaction processes |
| 7 | Heat dissipated by lighting | Moisture dissipated from various damp surfaces, liquid surfaces, or liquid streams |
| 8 | Latent heat generated along with various moisture dissipation processes |
[Reference] Control of the indoor thermal and humidity environment is achieved by supplying a certain amount of air into the room (called supply air) to remove the indoor heat and moisture loads, so that the heat and moisture of the indoor air reach a relatively balanced state and the indoor environmental parameters can be controlled within a certain range. Therefore, the supply air volume or supply air parameters of the air-conditioning system must be determined according to the heat and moisture load values of the air-conditioned room, and the supply air must be treated by air handling devices such as cooling, heating, dehumidification, and humidification. If the supply air volume is fixed, the load value determines the supply air parameters; if the supply air parameters are fixed, the load value determines the supply air volume. While removing heat and moisture disturbances, a certain amount of fresh air (called outdoor air) must also be supplied and a certain amount of indoor air (called exhaust air) must be discharged to keep the indoor air appropriately clean. In general situations, the makeup air volume is required to be greater than the exhaust air volume to prevent outdoor air from infiltrating, so that indoor cleanliness and other parameters are less affected by external conditions. For energy saving, part of the indoor air is often reused by returning it to the system to become part of the supply air; this portion of air is called return air.
7.1.7 Energy Saving of HVAC Systems
(1) Hospitals are high-energy-consumption buildings, and hospital loads include HVAC, water supply and drainage, electric power and lighting, and loads required for medical services. Among them, the medical-service loads include hot water supply, kitchen and catering supply, sterilization and disinfection, and laundry, mainly in the form of steam, with some using gas and electricity. The medical-service load is the largest load in the hospital, accounting for 25%～38% of the annual consumed load. In the past, attention was paid only to the fact that heat transfer and leakage from autoclaves, sterilizers, and hot piping would convert into air-conditioning loads; now the heat dissipation of large diagnostic and treatment equipment, new types of medical facilities (such as hydrotherapy rehabilitation rooms), large computer systems, and equipment in some bioclean room systems has all become Air-conditioning loads that cannot be ignored, thereby greatly changing the composition of the air-conditioning load of hospital buildings and the proportion of each component. With the modernization of hospitals in China, energy conservation in HVAC systems should receive great attention, especially in the following aspects:
1) The amount of fresh air required in hospitals is large and the requirements are high; some departments even require 100% fresh air. Many departments or sections also need to exhaust the dust, bacteria, odors, excess heat, excess moisture, and harmful gases they generate, so exhaust is required at many locations and in large volumes. Some departments also have strict positive pressure control requirements, and large amounts of fresh air are discharged outdoors as uncontrolled leakage air. Maintaining an appropriate positive pressure is the key to reducing the fresh air volume. If the positive pressure is too small, the clean space cannot be protected from intrusion by polluted outdoor air; if the positive pressure is too large, the fresh air makeup of the system increases and the fresh air load grows. To reduce fresh air energy consumption, how to reduce the fresh air volume, the exhaust volume, and the positive-pressure infiltration air volume while meeting the requirements has always been a major issue in hospital air conditioning. Besides reasonably determining the fresh air volume, variable fresh air volume control is currently an effective measure.
2) Where conditions permit, centralized pre-treatment of fresh air should be adopted. This not only makes it possible to collect high-quality fresh air and carry out effective air filtration, but also makes it very convenient to adopt different fresh air treatment methods according to the different seasons, or to use a total heat exchanger to pre-cool the fresh air; it also facilitates maintenance and management. Successful experience already exists abroad: not only can fresh air with stable parameters be provided, but the fresh air energy consumption is also greatly reduced.
3) Hospitals are full of waste hot water, cooling water, and condensate. For fear of cross contamination, these are generally not recovered to the boiler room for reuse. If the wastewater is collected centrally, and the low-temperature side of a heat pump is used to recover the heat contained in this wastewater while the high-temperature side at the other end upgrades the heat for re-supply, this is an indirect method of utilizing waste heat. It is independent of whether pollution exists in the waste heat and will not cause cross infection, so it is very suitable for hospitals. Although the investment is somewhat higher, the amount of waste heat recovered annually is considerable.
4) The distribution piping of heat supply systems is a major issue in energy conservation. Reasonable zoning and piping can shorten the transport distance; the number of flange joints and valves should be reduced as much as possible so as to minimize unnecessary pressure drops to the greatest extent. Strengthening pipe sealing and insulation, selecting good steam traps, and reducing "dripping, escaping, and leaking" in the pipes will lower the heat loss in transport. In addition, steam traps should not be installed in pipe shafts or ceilings, which can greatly reduce heat transfer and leakage and also lower the air-conditioning load of nearby rooms.
5) With the modernization of hospitals, more and more places in hospitals are adopting clean technology. Because of the large air volume and high resistance of purification systems, the transport energy consumption of the system has become the largest load of the air conditioning; in addition, the high fresh air ratio of purification systems results in a large fresh air load. Of these, the transport energy consumption of the system is a stable load, while the fresh air load varies with the seasons. The key to reducing the transport energy consumption of the system lies in reducing the supply air volume and the system resistance. Therefore, the required reasonable supply air volume should be calculated according to the actual situation, rather than estimated from the recommended air change rate. Moreover, the design air volume is calculated on the basis of the final resistance of the system filters; in actual operation, since the filters have not yet reached their final resistance, the operating air volume is usually far greater than the design air volume. Therefore, operating the fan at variable speed to achieve constant air volume operation of the system is of great energy-saving significance.
6) Although the supply air volume of the purification air-conditioning system is very large, distinguishing the air-conditioning air volume from the purification air volume within the system is also of great energy-saving significance. This is because the air-conditioning air volume in the supply air is mainly for removing the indoor heat and moisture loads and must be treated by the air handling unit, whereas the purification air volume is for meeting the cleanliness requirements and only needs to pass through re-filtration. The higher the class, the smaller the proportion of the air-conditioning air volume in the purification air volume. If the purification air volume is not returned to the machine room to be treated by the air handling unit but is returned directly to the cleanroom through a short cycle, transport energy can be saved very effectively, and this is even more remarkable in high-class cleanroom systems. Eliminating the heat generated by the fan motors from the purification air-conditioning system also has a considerable energy-saving effect; measures such as placing the fan motor outside the air handling unit and not using fan-powered filter supply outlets in the system can also effectively reduce the heat generated by the fans. For low-class cleanrooms, low-resistance sub-high-efficiency filters should be used as far as possible, which can greatly reduce the system resistance and thus reduce the fan output power.
7) Many cities are revising their electricity tariff systems and adopting time-of-use electricity pricing; using the price difference between day and night for ice storage or heat storage has promoted the development of thermal energy storage technology, and the more successful examples are the dual-condition screw chiller units and their cool storage equipment. There are various types of ice storage, such as the ice coil type (direct-evaporation ice storage system), the complete freezing type, the ice ball type, and the ice harvester type. Before determining the ice storage operation mode, the hourly air-conditioning cooling load of the building must first be calculated fairly accurately and a load diagram drawn; then the mode of operation should be determined according to the local electricity usage periods, investment requirements, and so on. Generally, there are two requirements: first, to maximize the electricity peak shaving and valley filling of the grid power supply, and second, minimizing the one-time investment. To find the optimal balance between these two conflicting objectives, time-based cold discharge is mostly adopted to satisfy both requirements. Generally, the cold discharge quantities during the two peak electricity consumption periods and during the peak air conditioning load must first be determined, and only then can the optimal cold storage capacity and the chiller capacity be determined, so as to maximize the peak-shaving and valley-filling effect and reduce the installed chiller capacity, thereby lowering the initial investment.
[Reference] Hot water storage pools (tanks) are also a form of energy storage. Installing a hot water storage pool can reduce equipment investment and operating costs, but to achieve energy savings, its use is limited to the following situations:
① When a heat recovery system can be utilized.
② When no fossil fuels are used, such as solar heating.
③ When inexpensive late-night electricity or factory waste heat is available.
Conversely, since the hot water storage pool system consumes the following additional energy, it is not energy-saving except in the above-mentioned cases:
① The hot water storage pool has an energy loss of more than 10% over a continuous 24h period.
② Because an open water circuit must be adopted, the pump head has to be increased, resulting in a sharp increase in pump power.
(2) For some energy-saving methods in hospitals, the feasibility of their application, and possible problems, see Table 7.6.
Table 7.6 Energy-Saving Methods for Hospitals and Their Feasibility
| System | Energy-Saving Method | Feasibility and Effect of Application in Hospitals | Existing Problems |
|---|---|---|---|
| Cooling and heating source system | Selecting appropriate capacity and number of units so that equipment maintains high-efficiency operation in all seasons | At partial load (0.5), operating efficiency ≥80% | Too many units increase investment and plant room area |
| Cooling and heating source system | Selecting equipment with high coefficient of performance | Depends on the ratio of price and maintenance cost to benefit | |
| Cooling and heating source system | Flexible use of natural energy (solar energy, groundwater, etc.) | Depends on the natural energy conditions of the region | Ground subsidence, groundwater pollution |
| Cooling and heating source system | Effective use of thermal (cold) storage | Depends on occupied area, electricity price differential, and benefits | Increases investment and plant room area |
| Cooling and heating source system | Heat recovery heat pumps (waste gas, condensate water, cooling water, etc.) | Suitable for places with strict drainage planning | If waste heat sources are scattered, systematic recovery is difficult |
| Cooling and heating source system | Adopting absorption chillers | Full use of surplus steam in summer | Saves electricity but not energy; pay attention to environmental pollution from boilers |
| Distribution system | Transporting water is more energy-efficient than transporting air | Use water systems as much as possible for transporting cooling and heating sources | Indoor fan coil units are unfavorable to aseptic conditions |
| Distribution system | Increasing transport temperature difference to reduce transport volume | Use cold storage to lower the temperature of the transport medium | Pay attention to the performance of terminal units |
| Distribution system | Variable flow transport | Use variable water flow regulation as much as possible in air conditioning systems | Pump speed regulation devices are relatively expensive |
| Distribution system | Insulation of transport pipelines | Adopt the optimal insulation thickness | Pay attention to the fire performance of insulation materials |
| Air conditioning system | Most appropriate system zoning | Zone according to hospital characteristics | Pay attention to reverse air flow between zones when zone systems are shut down |
| Air conditioning system | Variable outdoor air volume regulation | Beneficial to improving indoor air quality | Difficult to apply in non-centralized systems |
| Air conditioning system | Adopting total heat exchangers | Pay attention to the layout of outdoor air and exhaust air ducts in design | Leakage of polluted air in total heat exchangers |
| Air conditioning system | Adopting purification technology to increase return air volume | Provided the minimum outdoor air volume is guaranteed, the system outdoor air volume can be reduced | Some indoor pollutant gases are difficult to remove effectively |
| Air conditioning system | Reducing mixing losses and reheat losses | Reasonable zoning | Increases system complexity |
| Air conditioning system | Improving outdoor air quality to reduce system outdoor air volume | Intake high-quality outdoor air, reduce transport distance and pollution along the way | |
| Control system | Setting the optimal start time and operation time | Significant energy-saving effect for departments with intermittent operation | For areas with gradient pressure difference requirements, control should be applied cautiously |
| Control system | Selection of the optimal equipment ratio (number of units, capacity) | ||
| Control system | Setting the optimal supply air parameters | Adopt the air volume priority regulation mode | Many departments are not suitable for variable air volume operation |
| Control system | Setting the optimal operating conditions according to climate changes | Significant energy-saving effect | Operating modes are overly complex, increasing management difficulty |
| Control system | Rooms are generally equipped with thermostats; some require temperature and humidity controllers | Occupants can set the temperature (and humidity) themselves | Controllers are easily damaged by frequent adjustment |
[Reference] The insulation of equipment and pipes shall be calculated in accordance with the Guide for Design of Thermal Insulation of Equipment and Pipes (GB8175-87). Generally They may be selected according to Tables 7.7–7.10, and the thickness shall not be less than the values given in the tables.
Table 7.7 Economic Insulation Thickness for Air-Conditioning Cooling Pipes
| Insulation Material | Annual Cooling Hours/h | Nominal Diameter/mm | Economic Insulation Thickness/mm |
|---|---|---|---|
| Rubber-plastic pipe shells and flat boards | 2 880 | 15～32 | 19 |
| Rubber-plastic pipe shells and flat boards | 2 880 | 40～150 | 25 |
| Rubber-plastic pipe shells and flat boards | 2 880 | 200～500 | 32 |
| Rubber-plastic pipe shells and flat boards | 3 600 | 15～50 | 25 |
| Rubber-plastic pipe shells and flat boards | 3 600 | 65～150 | 32 |
| Rubber-plastic pipe shells and flat boards | 3 600 | 125～500 | 38 |
| Rubber-plastic pipe shells and flat boards | 4 320 | 15～100 | 32 |
| Rubber-plastic pipe shells and flat boards | 4 320 | 125～500 | 38 |
| Centrifugal glass wool pipe shell (64kg/m³) | 2 880 | 15～50 | 25 |
| Centrifugal glass wool pipe shell (64kg/m³) | 2 880 | 65～150 | 30 |
| Centrifugal glass wool pipe shell (64kg/m³) | 2 880 | 200～500 | 35 |
| Centrifugal glass wool pipe shell (64kg/m³) | 3 600 | 15～50 | 30 |
| Centrifugal glass wool pipe shell (64kg/m³) | 3 600 | 65～150 | 35 |
| Centrifugal glass wool pipe shell (64kg/m³) | 3 600 | 200～500 | 40 |
| Centrifugal glass wool pipe shell (64kg/m³) | 4 320 | 15～50 | 35 |
| Centrifugal glass wool pipe shell (64kg/m³) | 4 320 | 65～150 | 40 |
| Centrifugal glass wool pipe shell (64kg/m³) | 4 320 | 200～500 | 50 |
Table 7.8 Minimum Insulation Thickness for Ice Storage System Pipes
| Insulation Material | Annual Cooling Hours/h | Nominal Diameter/mm | Economic Insulation Thickness/mm |
|---|---|---|---|
| Rubber-plastic pipe shells and flat boards | 2 880 | 15～32 | 25 |
| Rubber-plastic pipe shells and flat boards | 2 880 | 40～150 | 32 |
| Rubber-plastic pipe shells and flat boards | 2 880 | 200～500 | 38 |
| Rubber-plastic pipe shells and flat boards | 3 600 | 15～25 | 32 |
| Rubber-plastic pipe shells and flat boards | 3 600 | 32～50 | 38 |
| Rubber-plastic pipe shells and flat boards | 3 600 | 65～150 | 41 |
| Rubber-plastic pipe shells and flat boards | 3 600 | 200～500 | 45 |
| Rubber-plastic pipe shells and flat boards | 4 320 | 15～50 | 38 |
| Rubber-plastic pipe shells and flat boards | 4 320 | 65～150 | 41 |
| Rubber-plastic pipe shells and flat boards | 4 320 | 200～500 | 45 |
| Centrifugal glass wool pipe shell | 2 880 | 15～125 | 40 |
| Centrifugal glass wool pipe shell | 2 880 | 150～500 | 50 |
| Centrifugal glass wool pipe shell | 3 600 | 15～50 | 40 |
| Centrifugal glass wool pipe shell | 3 600 | 65～500 | 50 |
| Centrifugal glass wool pipe shell | 4 320 | 15～100 | 50 |
| Centrifugal glass wool pipe shell | 4 320 | 125～500 | 60 |
Note: The coolant temperature of the ice storage system is $-6,^circtext{C}$, and the thermal conductivity of the materials is:
- Flame-retardant polyethylene $lambda = 0.036 + 0.001t_m,[text{W/(m·℃)}]$
- Rubber-plastic $lambda = 0.0375 + 0.00125t_m,[text{W/(m·℃)}]$
- Polyurethane foam $lambda = 0.035 + 0.00125t_m,[text{W/(m·℃)}]$
Where: $t_m$ refers to the mean temperature of the insulation layer, generally calculated as the average of the temperature of the medium inside the pipe and that of the surrounding air.
Table 7.9 Economic Insulation Thickness for Air-Conditioning Ducts
| Insulation Material | Annual Cooling Duration/h | Economic Insulation Thickness/mm |
|---|---|---|
| Centrifugal glass wool pipe shell (32kg/m³) | 2 880 | 30 |
| Centrifugal glass wool pipe shell (32kg/m³) | 3 660 | 40 |
| Centrifugal glass wool pipe shell (32kg/m³) | 4 320 | 50 |
| Rubber-plastic flat sheet | 2 880 | 16 |
| Rubber-plastic flat sheet | 3 600 | 19 |
| Rubber-plastic flat sheet | 4 320 | 21 |
Table 7.10 Economic Insulation Thickness for Low-Temperature Supply Air Ducts of Air-Conditioning Systems
| Insulation Material | Annual Cooling Duration/h | Economic Insulation Thickness/mm |
|---|---|---|
| Centrifugal glass wool pipe shell (32kg/m³) | 2 880 | 50 |
| Centrifugal glass wool pipe shell (32kg/m³) | 3 660 | 60 |
| Centrifugal glass wool pipe shell (32kg/m³) | 4 320 | 70 |
| Rubber-plastic flat sheet | 2 880 | 21 |
| Rubber-plastic flat sheet | 3 600 | 25 |
| Rubber-plastic flat sheet | 4 320 | 32 |
Note: The supply air temperature is calculated based on 7℃.