The building energy consumption is an important part among the total society energy consumption, in which the energy consumption for air conditioning occupies almost 70%. The energy consumption of the air conditioning system for fresh air handling can be saved effectively when the exhaust air energy could be recovered to preheat or precool the fresh air. Considering the install locations requirements on field, the pump-driven heat pipes (PHP) were developed as heat recovery ventilators (HRVs) and used in an existing experiment building in Beijing Urban. The thermal performance of the PHP HRVs was tested in real operation time periods under winter running mode. Both the power and heat consumption of the modular air handling units with and without HRVs were monitored and obtained, as well as the hourly power and heat consumption. The energy savings of HRVs were analyzed. The results indicate that the PHP HRVs can work steadily and meet the energy recovery need well. The temperature effectiveness of the HRVs can be kept from 60% to 70%. The test total energy saving rate was 24.48%, and the average hourly heat consumption reduced by 28.54%. The daily energy consumption can be saved by 118 kWh, and the energy savings can reach to 9440 kWh for a whole winter.
The building energy consumption and proportion in total energy consumption increase year by year with development of total civil buildings and living standard. The energy saving in building field plays an important role to carbon peak achievement. The fresh air handling energy consumption of air conditioners is the main source for building energy consumption, which occupies almost 70% of the building energy consumption. Buildings using exhaust and fresh air systems for 24 h/day could benefit from air-to-air heat recovery ventilators (HRVs). Such recovery devices can reduce energy consumption by transferring 40% to 80% of the sensible and latent heat between the exhaust air and fresh air streams [
For the integral heat pipe owning high effectiveness, the fresh air and exhaust air ducts should be set up closely due to heat exchanger’s structure. When fresh air duct and exhaust air duct is apart or there are several fresh/exhaust air ducts, split heat pipe is available but integral heat pipe not. The split heat pipe is the development of conventional heat pipe, in which the low boiling-point substance is charged as working fluid for phase-change heat transfer assisted with capillary force or gravity. Chen et al. [
The investigations on PHP HRVs in buildings, especially for low temperature air to air heat exchanging, have been hardly indexed in publications. Zhou et al. [
The case building is an existing building with two floors for calibration experiments in Beijing Urban, which lies in semi-moist continental warm temperate monsoon climate with four distinct seasons. It is dry and windy in spring, hot and rainy in summer, cool in autumn, cold and dry in winter. The annual average sunshine time is 2684 h, the annual average temperature is 11.8°C, and the annual average precipitation is 550.3 mm. Three modular air handling units (MAHUs) run for air conditioning of the test room. The dry-bulb temperature and relative humidity requirements are 20 ± 1°C and <70%, respectively. The specifications of three MAHUs were listed in
MAHU |
Supply air volume(m3/h) | Supply fan power(kW) | Supply fan speed(r/min) | Exhaust air volume(m3/h) | Exhaust fan power(kW) | Exhaust fan speed(r/min) |
---|---|---|---|---|---|---|
K1 | 22500 | 15 | 1460 | 12000 | 2.2 | 935 |
K3 | 4500 | 0.75 | 910 | 3000 | 0.75 | 1410 |
K4 | 2800 | 0.55 | 1390 | 2000 | 0.55 | 1410 |
Thinking of the local policy and environmental requirements, for the case building the MAHUs work under the vapor compression refrigeration cycle to provide cool water in summer. In winter the electric boiler is used to produce hot water, which flows into the evaporators of the MAHUs to heat fresh air. Besides, the electric heating unit was an auxiliary in vent for fresh air heating. The MAHUs work for multiple rooms in different floor in daytimes (from 8:00 AM to 18:00 PM).
For the MAHUs in the above case building, three PHP HRVs were developed and installed as shown in
The following parameters were measured during tests: inlet and outlet fresh air temperatures, inlet exhaust air temperature, inlet and outlet pressures of liquid pump. The electricity meter for the air conditioning system including the HRV was read from the general power platform. The air temperature was gotten by Platinum resistance sensors (type PT100) and the test range of −30°C to 150°C connected to the control and data acquisition system. The interval of data acquisition was set as 1 min. The uncertainties were analyzed according to the standard deviation, and were calculated by the Class A evaluation method (statistical analysis method), and the results were listed in
Parameter | Temperature | Input power | Pressure | Temperature effectiveness | Energy consumption |
---|---|---|---|---|---|
Uncertainty | 0.29°C | 0.44% | 0.36% | 1.67% | 1.61% |
The performance of tested HRV was evaluated with temperature effectiveness ƞ and energy saving rate r. The equations were listed as follows:
The comparison tests were carried out in two days before and after according to the test plan. In the first test day, both the MAHUs and HRVs ran from 8:00 AM to 18:00 PM in 20th December, 2020. In the second test day, the MAHUs worked from 8:00 AM to 18:00 PM in 21st December, 2020, while the HRVs stopped in the same time. The power consumption and heat metering of the MAHUs with/without the HRVs were obtained through the independent energy consumption monitoring united platform. The dimension of heat metering data has been converted into kWh automatically by the platform. The data were acquired at 8:00, 11:00, 15:00 and 18:00, separately. And the record intervals were 3, 4 and 3 h, respectively. The operating pressure of the HRVs during tests remained in the range of 0.93 MPa to 1.64 MPa.
The energy consumption of the MAHUs and HRVs includes two parts, power consumption and heat consumption. Both the power and heat consumption were obtained from the independent energy consumption monitoring united platform, and the results were shown in
As shown in
The power consumption with the HRVs is higher than that without the HRVs, which was caused by the specific test conditions. During winter mode tests, the MAHUs remained at stand-by state, the heat water from electricity boilers supplied the heating source through the heat exchangers of the MAHUs to keep the building required constant temperature. When the supply air temperature is over the set air temperature point, the MAHUs would work for cooling to remain the constant supply temperature instead of the standby condition. Then the power consumption with the HRVs got increased. Besides, the HRVs power consumption was also monitored in the united platform and included in total power consumption. The total power difference between with and without HRVs was 5 kWh for entire test time.
Considering the difference of test time periods, the hourly power consumption and heat consumption of the MAHUs with and without HRVs were also presented in
The above test daily results were adopted and expanded to analyze the annual energy savings according to the running modes and energy saving rate. The detail running time for different modes were listed in
Running mode | Running date | Running days per month | Running time for one working day |
---|---|---|---|
Winter mode | December 15–March 15 next year | 20 days | 8:00–18:00 |
Name | Power meter | Power consumption/ kWh | Heat meter | Heat consumption/ kWh | Total energy consumption/ kWh | ||
---|---|---|---|---|---|---|---|
8:00 | 18:00 | 8:00 | 18:00 | ||||
MAHUs with HRVs | 499737 | 499793 | 56 | 20137 | 20445 | 308 | 364 |
MAHUs without HRVs | 499803 | 499854 | 51 | 20493 | 20924 | 431 | 482 |
Daily Energy Savings | −5 | 123 | 118 | ||||
Total Energy Savings | −400 | 9840 | 9440 |
The daily heat consumption can be saved by 123 kWh and the daily power consumption would increase by 5 kWh, which indicates the net daily energy saving as 118 kWh as shown in
The PHP HRVs were developed and installed in an existing experiment building to save the energy consumption of the MAHUs. The temperature effectiveness and energy savings were tested in real operations. The conclusions were drawn as follows:
The PLHP HRVs can meet the need of energy recovery for the MAHUs, and the temperature effectiveness of the HRVs varied in the range of 60%--70% at steady condition. The average temperature effectiveness in the morning was higher than that in the afternoon. The PHP HRVs can reduce the heat consumption obviously but increase the power consumption due to cooling power consumption to remain constant supply temperature. The test total energy saving rate including power and heat reached 24.48%. The hourly power consumption changed slightly with or without the HRVs, while the hourly heat consumption got reduced by 28.54% on average due to the HRVs adoption. The daily energy consumption can be saved by 118 kWh and the total energy savings can reach 9440 kWh for a whole winter.
Energy consumption before transform, kWh
Energy consumption after transform, kWh
Energy saving rate, %
Fresh air inlet temperature, °C
Fresh air outlet temperature, °C
Exhaust air inlet temperature, °C
Temperature effectiveness, %