(1) Institute of Air Conditioning, China Institute of Building Research; 2. Beijing Geology and Mineral Exploration and Development Company)
Abstract: With the development of air conditioning technology, the application of water source heat pump system is more and more extensive. In the existing large-scale buildings, cooling in summer and heating in winter are generally adopted, and heating with domestic hot water is rarely provided at the same time of cooling in summer. The water source heat pump system in the expert building of Friendship Hotel is not only used for air conditioning in summer, but also provides domestic hot water for the whole hotel park. The balance between heat and cold is fully considered in the design.
Water source heat pump system is widely used in air conditioning systems of various projects because of its advantages of energy saving and multi-purpose. The water source heat pump system uses shallow groundwater as the cooling water source of air conditioning in summer, and then recharges it underground; In winter, groundwater is the largest heat source, and part of the electricity input by the heat pump unit is used to heat the heating system. At present, the water source heat pump project basically realizes the use of a system in winter and summer, but in summer, the cold energy of well water is used and then directly discharged into the ground. However, if it can be used as heat for making domestic hot water, the energy saving of water source heat pump system will be further improved.
1 project overview
Beijing Friendship Hotel is the largest four-star garden hotel in Asia, located in Zhongguancun Street, the core of Zhongguancun High-tech Park. The newly-built expert building is located in the south of the hotel park, with a total construction area of 12724m? , including the new swimming pool and tennis court, with a total construction area of 2 1734m? . According to the calculation, the air conditioning load of the whole new project is 2537kW in summer and 3277.4kW in winter. At the end of the expert building, both heating system and fan coil plus fresh air system are used, and the swimming pool adopts floor heating system. The load borne by the whole computer room is as follows:
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sequential
2 system design
According to the requirements of Friendship Hotel, the system design needs to meet the following requirements:
(1) can meet the requirements of heating in winter and cooling in summer for the expert building and its affiliated buildings; Summer domestic hot water consumption in the park and annual domestic hot water consumption demand in the expert building.
(2) The winter heating of the expert building is divided into two parts: the low-temperature water source heat pump unit (R22) provides hot water for the fan coil unit+fresh air system, and the high-temperature water source heat pump unit (R 134a) provides hot water for the heating system;
(3) The high-temperature water source heat pump unit also provides domestic hot water for the expert building in winter, and the high-temperature unit is turned on to provide hot water for the expert building in transition season;
(4) In summer, the high-temperature unit gives priority to domestic hot water heating, and the cooling capacity is supplied to the air conditioning system, and the remaining cooling capacity is provided by the low-temperature unit. According to the above principles, the design system is as follows (figure 1):
In order to meet the operation requirements in different seasons, the system needs to be realized by switching valves and starting and stopping different pumps. During operation, it is divided into the following operating conditions:
(1) In summer, valves V 1, V3, V5 and V7 are opened, and V2, V4, V6, V8, V9 and V 10 are closed. The high-temperature unit ensures that the domestic hot water in the park uses heat, and the excess cold energy enters the air conditioning water circulation system of the expert building, and the insufficient cold energy is supplemented by the low-temperature unit. Well water is only used to provide cooling water for cryogenic units. The heating system of the expert building is turned off in summer.
(2) In winter, valves V2, V4, V6, V8, V9 and V 10 are open, and V 1, V3, V5 and V7 are closed. Well water is used as heat source for both high-temperature units and low-temperature units. The low-temperature unit supplies heat for the fan-coil air conditioning and fresh air system of the expert building and its annex building, and the high-temperature unit supplies heat for the heating system of the expert building.
(3) In the transitional season, open V2 and V4 and close all other valves. The high-temperature unit provides domestic hot water for the expert building, and well water also serves as the heat source.
2. 1 well water system
Well water system, as the main cold and heat source of the system, must meet the requirements of refrigeration and heating under any circumstances. In order to ensure the realization of all functions, five wells have been drilled, all of which are pumping irrigation wells, which can be used as both pumping wells and recharging wells. The new wells 1 and 3 are pumping wells, and the new well 4 is a spare well for pumping wells. The old wells No.3, No.4, No.5 and No.6, and the new wells No.2, No.4 and No.5 are used as recharge wells. The maximum load occurs in winter, and the required maximum hourly water consumption of well water is 400m3/h. According to the original data of well water, the maximum water output of a single well is 200 m3/h, and in general, the maximum water output of two wells is 400 m3/h, which is enough to meet the winter load. The maximum hourly water consumption in summer is 3 12m3/h, and the design temperature difference between winter and summer is 7℃. Under normal circumstances, the operation mode is two pumping and two irrigation. If the design load is exceeded, it can reach two pumping and three irrigation or three pumping and four irrigation.
Figure 1 heat pump system of new expert building in Friendship Hotel
2.2 unit selection
According to the cooling and heating load of Friendship Hotel, three low-temperature units of Tsinghua Tongfang SGHP 1800 A and three high-temperature units of HGHP 1200 A were initially selected.
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In actual operation, two low-temperature units or two high-temperature units+1 low-temperature units can be started during peak load in summer. At the peak of electricity consumption in winter, start two high-temperature units to supply heating system, and two low-temperature units to supply air conditioning heating. On the one hand, the redundant heat pump unit can be used as a system backup, on the other hand, it can be reserved for the air conditioning system of the reconstruction project.
3. Matching of cold and hot water of air conditioner
In the past, the water source heat pump system generally provided a single cold and heat source, and rarely used cold and heat at both ends. Therefore, under the premise of not affecting air conditioning refrigeration in summer, the domestic hot water system should adopt regenerative type, so that the use of air conditioning will not be affected when the domestic hot water load reaches the peak. At the same time, when the domestic hot water load is too large, too much cold energy can be dissipated, and a backup cooling system is also needed. Preliminary analysis shows that the domestic hot water load is much less than the air conditioning load in most of the time. Therefore, considering two factors, in the system design, we ensure that the high-temperature unit only ensures the supply of hot water, and the excess cooling capacity is provided by the low-temperature unit. However, when the hot water load is higher than the air conditioning load, there is no separate heat pump unit to provide it.
Before the design, through monitoring the domestic hot water of Friendship Hotel from August 12 to August 15, 2005, the hourly hot water consumption is as follows (Figure 2).
Figure 2 Load Table of Domestic Hot Water Consumption in Friendship Hotel
As can be seen from the above figure, the maximum hourly heat consumption of domestic hot water is concentrated between 7: 00 ~ 9: 00 in the morning and 16: 00 ~ 18: 00 in the afternoon. The maximum hourly water consumption is 37m3/h, and the longest peak duration is 2 hours. Domestic hot water is a relatively stable state quantity, and the air conditioning load will change with the change of outdoor temperature, and the air conditioning load will change greatly in different periods. Moreover, when the air conditioning load is lower than the hot water load, the standby situation is temporarily not considered in the preliminary design. Therefore, it is necessary to analyze under what circumstances the standby hot water heating system is needed.
Ignoring heat loss and useless work, the heating capacity of the unit is the sum of refrigeration capacity and input power. In order to ensure the stability of unit heating, we directly evaluate the balance between cooling capacity and heating capacity.
See Figure 2 for the comparison curve between the daily maximum air conditioning load and the average hot water load of the newly-built expert building. As can be seen from the figure, on the day when the maximum load is reached, the domestic hot water load is much lower than the air conditioning load at most times, except that the heating capacity is less than the cooling capacity between 22 o'clock at night and 1 point in the early morning, during which the hot water consumption is 55m3. The system uses a 52 cubic meter regenerative domestic hot water tank. Even if the air conditioning unit is not turned on at night, the domestic hot water stored in the hot water tank during the day can meet the requirements of hot water use at night.
By analyzing the matching situation under different air conditioning loads, it is found that when the air conditioning load is less than 55%, the heat pump hot water system can not meet the heat demand of domestic hot water in the whole park. Therefore, it is suggested to use the original gas-fired boiler to heat the hot water system when the air conditioning load is not higher than 55%.
4 Energy-saving effect analysis
The advantage of using water source heat pump instead of ordinary air conditioner is that the well water is maintained at about 65438 05℃ regardless of the outdoor temperature in summer, and the efficiency of water chiller is always maintained at a high level. Water source heat pump system is used in winter, most of the heat comes from underground, and the input electric energy only accounts for 25% ~ 30% of the total heat.
Taking this project as an example, the maximum cooling load is 2537kW and the maximum heating load is 3277kW. The comparison of air conditioning and heating costs under different modes is as follows:
Comparison of operating costs of different air conditioning forms under the same load in summer
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Comparison of operating costs of different heating methods under the same load in winter heating
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As can be seen from the above table, the hourly energy consumption cost of water source heat pump under the maximum load in summer is about 10% lower than that of central air conditioning, and more than 30% lower than that of sub-system air conditioning. The advantage of heating cost in winter is more obvious, which is 20% lower than that of natural gas boilers.
If calculated according to a heating season (150 days), it can be concluded that the operating costs of several heating modes in the newly-built expert building are as follows: oil-fired boiler, 45.23 yuan/m2; Gas boiler, 27.6 1 yuan/m2; Air-cooled heat pump, 36.68 yuan/m2; Water source heat pump, 2 1.09 yuan /m2.
Figure 2 Comparison table of maximum daily cooling load and domestic hot water load
It can be seen that in the existing heating methods of Friendship Hotel, the water source heat pump is the most energy-saving and the operating cost is the lowest.
There is little difference between water source heat pump and other central air conditioners in summer, just because the temperature of well water is relatively constant and the average refrigeration efficiency is higher than that of ordinary central air conditioners. However, Friendship Hotel gets some domestic hot water free of charge while getting air conditioning because it uses condensation heat to heat domestic hot water.
According to the analysis results of domestic hot water, when the daily total load of air conditioning reaches more than 55% of the maximum daily total load, the hot water generated by the waste heat of air conditioning can provide domestic hot water for the whole park. In summer, when the daily total load of air conditioning is above 55% of the maximum daily total load, it is about 60%, and the average load value is calculated as 75%. The domestic hot water at 50℃ is about 35220m3. Because the daily domestic hot water quantity is basically unchanged, the effective domestic hot water quantity used in each season is about 30,000 m3, which can save gas165,900 m3 and cost about 3152,000 yuan. At present, the operation mode is that when the air conditioning load is low, the heat pump unit and the gas boiler supply heat at the same time, and when the air conditioning load is high, only the heat pump unit provides hot water. This operation mode will further save energy and accelerate the investment recovery on the existing basis.
At present, the air conditioning system of the expert building is not fully put into use, so it is impossible to know the operating cost of air conditioning in detail. However, according to the records from July 8 to July 20, the total electricity consumption of the whole computer room is considered to be all used for heating domestic hot water, and the cost per cubic meter of hot water is 20.23 yuan. If calculated in this way, it is equivalent to investing 20.23 yuan /m3 of hot water every day, and the supplied air-conditioning cooling capacity is obtained free of charge. It can be seen that the water source heat pump system of Friendship Hotel has a good energy-saving prospect.
5 conclusion
(1) Water-source heat pump system has a higher energy efficiency ratio than conventional central air-conditioning system in summer because of its relatively constant groundwater temperature and high reliability.
(2) It is feasible to heat domestic hot water by using the heat of heat pump condenser in summer. In the case of giving priority to domestic hot water system, the heat pump hot water supply system can only be started after the air conditioning load reaches a certain requirement. In the case of low load, it is suggested to adopt other heating methods or set up a heat pump with single hot water supply separately.
(3) Using high temperature condensation heat to heat domestic hot water system in summer can reduce the utilization of groundwater. Compared with the system without domestic hot water, it only increases the investment of board replacement and can bring huge benefits to users.
(4) Among several heating modes in winter, due to the constant groundwater temperature, the heat pump unit can use a lot of low-grade heat energy to reduce the amount of electric energy, and the operating cost is the lowest among several heating modes. Therefore, in areas with abundant underground resources and good recharge conditions, it is suggested to give priority to this heating method.