Chapter 5 Field measurement
5.2 Method and case descriptions
5.3.4 Heat leakage through the duct system
Ventilation plays a significant role in buildings to create a thermally comfortable environment by regulating indoor air parameters such as temperature, RH, and air movement.
Inevitably, duct heat leakage and consequent energy losses will always happen through the
0 200 400 600 800 1000 1200
0 12 24 36 48
Outdoor CO2 concentration Indoor CO2 concentration
0 10 20 30 40 50 60 70
working period
8:30-17:00 Occupant density
CO2 concentration [ppm]
Time [h]
Occupant density
ventilation system.
Here, in order to discuss the overall trend of sensible/latent heat transfer in the ventilation duct system, the typical distributions of temperature and RH at each measurement point are shown in Figure 5.12. The average outdoor air temperature in February 2008 during the daytime was 3.2°C, and the values in Figure 5.12 were selected when outdoor air temperature was as close to 3.1°C as possible. The values in Figure 5.12 are the time averages of 1-hour measurements, not the instantaneous values.
Concerning the results of Case 2 in Figure 5.12 (2), the outdoor air temperature (3.1 °C) increased after it passed through the outdoor air (OA) duct, the ERV and supply air (SA) duct, and finally air at 10.2°C was supplied through the indoor terminal device. The temperature of the return air (RA) which is delivered by the indoor terminal device decreased from 24.6 °C through the RA duct, the ERV and the exhaust air (EA) duct, and finally air was released to the outdoors at 20.0°C. It was considered that sensible heat exchange occurred to some degree in Case 2 (without ERV) by passing through the attic space (space between the ceiling of the 1st floor and the flooring of the 2nd floor). Note that the temperature in the attic space was approximately 20°C.
On the contrary, in Case 1, as shown in Figure 5.12 (1), outdoor air at 3.2°C was introduced to the OA duct and passed through the ERV and SA duct, and finally air at 16.7°C was supplied indoors. The indoor air was taken into the RA duct at 24.9°C, and was finally released at 9.9°C. These temperature changes and differences are clearly distinguishable from the results of Case 2, without the ERV. In particular, the SA temperature rose from 10.2°C in Case 2 to 16.7°C in Case 1 with the ERV, and these temperature differences were indicative of the effectiveness of the installed ERV system. Note that the temperatures in the center of the room and attic spaces were almost the same in the two cases.
The relative humidity in the center of the room recovered from 27% RH without the ERV in Case 2 to 32% RH with the ERV in Case 1. Although this did not reach the standard value of 40% set in the "Law for Maintenance of Sanitation in Buildings," the latent heat recovery by
the ERV system was confirmed to some extent by comparing the results of Cases 1 and 2.
The typical distributions of temperature and relative humidity at each measurement point under summer conditions are shown in Figure 5.13. The data in both Figures 5.13 (1) and (2) were obtained when the measured outdoor air temperatures were similar, and at almost the same times. These values are also the average of 1-hour measurements, not instantaneous values. In Case 3 with ERV, it is clear that the SA temperature at the indoor device fell to 31.6°C as shown in Figure 5.13 (1). However, in Case 4 without the ERV system, the SA temperature at the indoor device was very close to the OA temperature, as shown in Figure 5.13 (2).
In order to clarify the heat transfer mechanism through the ERV system, sensible heat transfer rates in each part are also shown in Figure 5.12 and Figure 5.13. Inside the main body of the ERV device, the total heat levels (including sensible and latent heat) are indicated in parentheses because there is a latent heat transfer through the ERV system.
(1) Case 1 with ERV system (6th Feb) (2) Case 2 without ERV system (15th Feb)
Figure 5.12 Temperature and humidity distributions in the ventilation duct system (Winter conditions)
21.5oC 30.8%
4.9g/kg(DA)
3.2oC 59.7%
2.8g/kg(DA)
16.7oC 36.6%
4.3g/kg(DA) Center
22.3oC 31.8%
5.3g/kg(DA) 17.2oC 34.3%
4.2g/kg(DA)
24.6oC 26.3%
5.0g/kg(DA) Attic space
20.0oC 31.7%
4.6g/kg(DA)
29.9oC 19.2%
5.0g/kg(DA) 2.6oC
67.0%
3.0g/kg(DA) 4.5oC 64.6%
3.4g/kg(DA)
24.9oC 24.5%
4.8g/kg(DA) 9.9oC
53.7%
4.0g/kg(DA)
Heat pump AC under
unit 15.4oC 41.0%
4.4g/kg(DA) with
ERV RA
SA EA
OA
2F
1F Insulation
1F EA
OA Heat pump AC
2F 22.4oC
26.5%
4.4g/kg(DA)
3.1oC 60.8%
2.9g/kg(DA)
6.2oC 53.7%
3.1g/kg(DA) 2.6oC
65.3%
3.0g/kg(DA) 19.6oC 30.8%
4.3g/kg(DA) 20.0oC
31.9%
4.6g/kg(DA)
Attic space 19.6oC 27.0%
3.8g/kg(DA)
10.2oC 38.2%
2.9g/kg(DA) Center
22.3oC 27.0%
4.5g/kg(DA)
24.9oC 20.8%
4.0g/kg(DA) 31.7oC 12.0%
3.5g/kg(DA) 24.6oC
21.2%
4.0g/kg(DA) Insulation
under unit 16.2oC 36.0%
4.1g/kg(DA) without
ERV
RA
SA
2F
247W With ERV
1117W (1337W) 1370W (1689W) Attic space
OA EA RA
SA
43W 39W
471W
1F
2F
156W Without ERV
283W (319W) 219W (239W) Attic space
OA
RA EA
SA
36W 313W
32W
1F
Heat leakage from the duct surface in Case 2 has been confirmed in winter conditions (Figure 5.12). This can be attributed to the large temperature differences between inside (office room space) and outside (outdoor environment), and also between the under layer of the roof and the room floor surface (about 5°C). In Case 1, a sensible heat exchange rate of 1000 W or more was observed with respect to the ERV device.
In Case 4, temperature differences between the under layer roof space and the outdoor environment in summer conditions were small (Figure 5.13) and correspondingly, ventilation duct heat leakage was likewise observed to be small. The heat transfer through each of the RA and EA ducts was about 70 W. There was little heat leakage inside the main body of the ERV device. In Case 3 with ERV, the heat losses through the OA and EA ducts were confirmed to be about 50 W with about 120–190 When heat exchange in the ERV device.
(1) Case 3 with ERV system (4th Aug) (2) Case 4 without ERV system (30th Jul)
Figure 5.13 Temperature and humidity distributions in the ventilation duct system (Summer conditions)
28.8oC 54.6%
13.5g/kg(DA)
32.6oC 46.6%
14.4g/kg(DA)
30.1oC 50.2%
13.5g/kg(DA) Center
28.0oC 55.7%
13.2g/kg(DA) 30.1oC 53.1%
14.2g/kg(DA)
27.6oC 57.6%
13.3g/kg(DA) Attic space
29.0oC 55.7%
14.0g/kg(DA)
19.5oC 94.2%
13.4g/kg(DA) 31.8oC
649.2%
14.6g/kg(DA) 31.3oC 51.6%
14.8g/kg(DA)
28.8oC 51.4%
12.7g/kg(DA) 32.0oC
48.7%
14.5g/kg(DA)
Heat pump AC
Insulation
under unit 29.1oC 55.4%
14.0g/kg(DA) with
RA
SA EA
OA
2F
1F ERV
1F EA
OA Heat pump AC
2F 29.9oC
52.6%
14.0g/kg(DA)
31.5oC 49.8%
14.5g/kg(DA)
31.4oC 51.4%
14.8g/kg(DA) 31.5oC
50.9%
14.8g/kg(DA) 29.5oC 52.7%
13.7g/kg(DA) 30.4oC
50.4%
13.7g/kg(DA)
Attic space 28.8oC 58.2%
14.4g/kg(DA)
30.9oC 50.2%
14.0g/kg(DA) Center
28.2oC 54.4%
13.1g/kg(DA)
27.5oC 57.1%
13.2g/kg(DA) 22.1oC 80.9%
13.5g/kg(DA) 28.9oC
51.2%
12.8g/kg(DA) Insulation
under unit 29.2oC 54.9%
14.0g/kg(DA) without
ERV
RA
SA
2F
2W With ERV
121W (185W) 189W (434W) Attic space
OA
RA EA
SA
50W 1W
52W
1F
2F
72W Without ERV
9W (2W) 29W (84W) Attic space
OA EA RA
SA
0W 37W
69W
1F
(a)Winter (b) Summer
Figure 5.14. Comparisons of duct heat leakage between ERV and non-ERV cases Figure 5.14 denotes heat leakage that was estimated by the temperature differences between intake and outflow air at each ventilation duct, and airflow rates through the ventilation ducts.
High heat leakage through the supply air (SA) and return air (RA) ducts, resulting from no heat insulation and the extremely low temperature in the attic space where the ERV systems are installed, were observed in winter conditions.
With a well-insulated outdoor air (OA) intake duct, heat leakage was less than 50 W in both the ERV and non-ERV cases. No moisture leakage from the surface of each duct was observed throughout the measurements, and hence these heat leakage values indicated sensible heat loss here. Due to inconspicuous indoor-outdoor temperature differences, heat leakagewas alleviated during the summer and the heat leakage rates through the supply air (SA) and return air (RA) ducts (about 30–70 W).
-600 -400 -200 0 200 400 600
Heat leakage from ducts [W] Without ERV With ERV Insulated
duct
OA SA RA EA
Insulated duct
-600 -400 -200 0 200 400 600
Heat leakage from ducts [W] Without ERV
With ERV
Insulated duct
OA SA RA EA
Insulated
On the other hand, night cooling, applied to reduce indoor contaminants, allowed for a reasonable air ventilation rate, for stored heat to be expelled from the building envelope.