ctbuh.org/papers Title: Authors: Subject: Keywords: The Evaluation of Performance for the Application of a Heat Recovery Ventilator to High-rise Apartments Sang-Min Kim, Principal Research Engineer, Hyundai Engineering & onstruction Heung-Don Ham, Professor, Daewon Plus onstruction Jang-Yeul Sohn, Professor, Hanyang University MEP Energy Efficiency MEP Publication Date: 24 Original Publication: Paper Type: TBUH 24 Seoul onference 1. Book chapter/part chapter 2. Journal paper 3. onference proceeding 4. Unpublished conference paper 5. Magazine article 6. Unpublished ouncil on Tall Buildings and Urban Habitat / Sang-Min Kim; Heung-Don Ham; Jang-Yeul Sohn
The Evaluation of Performance for the Application of a Heat Recovery Ventilator to High-rise Apartments Sang-Min Kim 1, Heung-Don Ham 2, Jang-Yeul Sohn 3 1 Principal Research Engineer, Hyundai Institute of onstruction Technology 2 Professor, Dept. of Indoor Environment Design, Daewon Science ollege 3 Professor, Architectural Environmental Engineering Lab., Hanyang University Abstract The individual HVA system and HRV has been installed in Korean apartment, but not the central cooling, heating and ventilation system which is operating in the most of office buildings. According to the heat exchange effectiveness of HRV and the operating method of HRV, it is possible to not reducing the energy reasonable way in Korea, which has four distinctive seasons. In this study, the optimum schedule for operating an HRV system that would save the most energy and sustain a reasonable rate of air exchange during the summer and winter was investigated Laboratory and field efficiency tests and some simulations were conducted for determining the optimum operating conditions for the HRV. A reduction of 15% in heating energy during the winter test period and a 1% reduction in cooling energy in summer test period were achieved. The results of the L show that operating the HRV 24 hours a day is the most economical method. Keywords: HRV, Energy-saving, Heat-recovery, L, ross-contamination 1. Introduction In Korea, high-rise apartment buildings up to 7-stories high are being constructed. Over the years, the air tightness of the windows and building surfaces has improved, and now these buildings appear to be energy efficient. However, other factors, such as the rate of infiltration and leakage, affect energy efficiency. Though the air-tightness of the windows and the building surfaces has improved over the years, the rate of infiltration and leakage has been falling accordingly. The combination of improved air tightness and increased infiltration and leakage, will cause contamination of indoor air unless an air ventilation strategy is applied. One air ventilation strategy that is being currently installed in apartment buildings is the HRV (Heat Recovery Ventilator). The HRV can save energy and improve the indoor air quality. The HRV is installed at each household for the first time. The individual cooling, heating system and HRV has been installed in Korean apartment, but not the central HVA system which is operating in the most of office buildings. Korea has four distinct seasons. Summers are hot and humid and winters are cold and dry. ontact Author: Sang-Min Kim Principal Research Engineer Hyundai Institute of onstruction Technology 12-4 Mabukri, Goosungeup, Yonginsi, Kyunggido, 449-716, Korea Tel: 82-31-28-7355 Fax: 82-31-28-77 e-mail: smkim@hdec.co.kr Therefore, a system is needed that can operate efficiently in both extremes. Factors that can affect the efficiency of the system are the heat exchange of the material, the specific alternation rate of heat exchange due to external temperature, humidity and the method of operation. Operating HRV according to the Ventilation Air Requirements (ANSI/ASHRAE Standard 62.2-23) could be reasonable condition to saving energy and improving indoor air quality. This investigation attempts to determine the optimum operating conditions for a HRV that save energy and supply reasonable out door air requirements with respect to the external air temperature and the humidity of Korea, but not full time of the year. 2. Methods 2.1 The efficiency test due to the regulation The fixed-plate type of HRV is the most commonly used system among the variety of HRV systems installed in high-rise apartment buildings in Korea. The following 2 methods have been used to laboratory test the HRV samples in this study: - BS EN 38 : Heat exchanger-test procedures for establishing the performance of air to air and flue gases heat recovery devices - AN/-439-88 : Standard Methods of Test for Rating the Performance of Heat-Recovery Ventilators The contents of the 2 regulatory methods governing TBUH 24 October 1~13, Seoul, Korea 63
performance tests are shown below. - Airflow Measurements - External / Internal Leakage Tests - Internal Exhaust Air Leakage Tests - Pressure Drop Tests - Temperature and Humidity Ratio Tests - ross Air Leakage Tests(Tracer Gas Tests) A simplification of real airflow in an HRV is shown in Fig.1. The net air volume has been calculated by the equation (1) ~ (6). The results of net air volume are adjusted in the efficiency calculation. OA q c c q h c : Net Supply Air h : Net Exhaust Air q c : Leakage mass flow rate from supply air to exhaust air q h : Leakage mass flow rate from exhaust air to supply air : Air mass flow rate at supply air EA : Air mass flow rate at exhaust air : SF 6 oncentration at supply air OA : SF 6 oncentration at outdoor air RA : SF 6 oncentration at return air Two models, a sensible heat exchanger and a total heat exchanger, were selected to test the application efficiency in the field. According to the laboratory test result, these HRVs have almost equal amount of airflow, pressure drop and below the 5% of cross air leakage rate. EA Fig. 1. Air Leakage in HRV h RA 2.2 The application efficiency test on the field 1) Field measurement summary The air volume measured in supply air is equal to the sum of RA-EA air-side leakage air( q h ) and the net supply air volume( c ). The equation of the result is shown Equation (1). Also, because the concertration of the SF6 in net supply air volume( OA ) and the SF6 concertration in the RA-EA air-side leakage air( RA ) is equal to the SF6 concertration in ( ), the equation can be shown as Equation (2). The Equation (3) and (4) could be made from simultaneous calculation of the Equation (1) and (2). Also the Equation (5) and (6) could be gained due to the simultaneous equation of air volume of EA and the SF6 concertration of EA. (a) A-Apartment + q = h (1) + q = OA RA h (2) = (3) RA OA RA q OA h = (4) RA OA EA OA h = EA (5) RA OA q EA RA c = EA (6) OA RA (b) B -Apartment Fig. 2. Floor plan of apartment and schematic of HRV 64 TBUH 24 October 1~13, Seoul, Korea
The test was conducted in each room in 2 high-rise apartment units, which have the typical HVA system. In each unit a package air-conditioner, hot water floor heating panel(ondol) and the HRV for ventilation have been installed. The floor plane of apartment is shown on Fig.2 and the area of each room and ventilation are shown in Table.1. The same identical HRVs as tested in the laboratory were installed to the each apartment. The total heat recovery ventilators were installed in the two units, the upper and lower floors (39th floor, 4th floor) in the apartment A, sharing the same architectural factors such as area and direction, etc. Heat exchanger performance was measured during the summer from June 6 to August 3, 23. A package air conditioner was used to control the indoor temperature which was maintained at 26. However, the humidity was not controlled. The sensible heat exchanger was installed in the 2 units, the upper and lower floors in the apartment B, sharing the same architectural factors such as area and direction, etc. The performance of the heat exchanger was measured during the winter from January 9 to February 28, 24). The hot water floor heating panel (Ondol) was used to control the indoor temperature, which was maintained at 2. Table 1. Area and air change rate(ah) in apartments Apartment Room Area(m 2 ) AH Room1 28.51 Room2 22.46 A Apartment B Bpartment Room3 13.53 Room4 15.52 Living Room 29.51 Dining Room 11 1.93 Etc. 56 - Total 174 - Room1 17.51 Room2 3.49 Room3 27.53 Room4 16.49 Living Room 35.54 Dining Room 14 1.87 Etc. 96 - Total 235 - However, the humidity wasn't controlled. In order to measure the energy saving efficiency of HRV, the tests were conducted under two different conditions. Under the first condition, the HRV was turned on for 24 hours in upper floor (ase 1). Under the second condition, the same amount of wind of OA was forced inside without passing through the HRV in lower floor (ase 2). The air exchange rate was maintained at.5 AH in both of ase 1 and ase 2. The temperature, the humidity, heating and cooling energy consumption, electric energy consumption of HRV fan, air volume and air exchange rate were measured to evaluate performance. 2.3 S/W Simulation The simulation was used to estimate the yearly energy consumption according to the operating schedule of HRV(Fig.3) under the condition of Korean climate. The simulation schedule cases are shown below. 1) Schedule A, B : The operating condition to maximize total heat exchange efficiency of HRV 2) Schedule, D : The operating condition to intake maximum outdoor air is necessary to eliminate pollutants generated from occupants and cooking activity. 3) Schedule E : The operating condition to intake the reasonable outdoor air for 24 hours without considering outdoor air temperature and humidity. 4) Schedule F, G : The operating condition of HRV turned on/off for 24 hours to compare the field measurement result heating and cooling energy consumption during the summer term(3 months) and winter term(2 months). Figure 3 shows the 7 HRV operating schedules. In the laboratory, the total heat exchanger efficiency performance was measured at about 5%, which was the same as determined by the simulation. 3. Results 3.1 Results of efficiency test in the test chamber 1) Airflow Measurements and Pressure Drop Tests The air volume of HRV and pressure drop were Fig. 3. HRV on/off schedule TBUH 24 October 1~13, Seoul, Korea 65
measured according to ASHRAE Standard 41.2-1987 (RA92). Table 2 shows the air volume of HRV and pressure drop in apartments A and B. Table 2. Airflow and Pressure Drop Tests Results OA RA EA A-HRV Airflow(l /s) 48.6 46. 49.3 51.5 (A-Apartment) Pressure Drop 15.3(15pa) 15.7(154pa) B-HRV Airflow(l /s) 53.2 53.3 57.8 63.1 (B-Apartment) Pressure Drop 16(157pa) 16.6(162.8pa) 2) External / Internal Leakage Tests External/internal leakage was measured in 5pa increments from to 25pa using a pressure chamber. External leakage was measured as 4.6%, 3% in ± 25pa of the mass flow rate. The results from apartment A are shown in figure 4. Leakage Airflow[l/s] 2.5 2. 1.5 1..5. -25-2 -15-1 -5 5 1 15 2 25 Pressure [Pa] Fig. 4. Result of external leakage tests(a-apartment) 3) ross Air Leakage Tests and net air volume ross air leakage was measured between the OA- and the RA-EA. A tracer gas test was conducted in OA,, RA, EA air-side, using SF6 gas. The net air volume was calculated using equations (1) (6) and the results of measurement are shown in table 3. Table 3. Air leakage and net air volume Airflow(l /s) % of Air leakage Heat tranfer type H q q h OA-(q h ) RA-EA(q c ) A-HRV 44. 5.5 1.1 2. 4.4 2.1 (Total HRV) B-HRV 5.7 61. 2.1 2.6 4.9 3.3 (Sensible HRV) 4) Temperature and Humidity Ratio Test In order to measure the heat exchange efficiency, the temperatures at the exhaust air inlet and the supply air inlet were set at 25 of and 5, respectively. The electric pre-heater was turned off during the measurement despite the low temperature. The efficiency of total heat exchange of the 2 HRVs were about 5%, and cross air leakage was calibrated. The detailed information is shown in table 4. Table 4. Results of HRV Performance A-HRV A apartment B-HRV B apartment Static pressure(mmaq) 8.8(86pa) 9.6(94pa) Heat tranfer type Total heat Sensible heat exchanger exchanger Airflow(l /s) 46. 53.3 Operating mode High/Middle/Low High/Middle/Low Electric energy(w) 198(High mode) 21(High mode) Points of supply diffuser 5points 6points Points of return air diffuser 3points 3points ondition High temperature room 25 / Low temperature room 5 Sensible heat effectiveness 69.2 66.3 Total heat effectiveness 51. 5.4 3.2 Results of field measurement and simulation A comparison of the results of case 1 (HRV turned on for 24 hours) and case 2 (HRV turned off for 24 hours) were analyzed for both apartments A and B. Figure 5 shows the temperature, humidity and heating energy consumption patterns of case 1 and case 2 on a certain day of winter in apartment B. Figure 6 shows the temperature, humidity and cooling energy consumption patterns of case 1 and case 2 on a certain day of summer in apartment A. The total heat exchange efficiency was reasonable during the hours of 12 and 15, heating energy consumption was 15% lower than case 2. The temperature, humidity and heating energy consumption patterns were measured and analyzed for summer of apartment A. The total heat exchange efficiency was less than the winter term. The cooling energy consumption was 1% lower in case 1 than case 2. Figure 7 and table 5 show the measurement result of monthly energy consumption in both cases 1 and 2. According to the field measurements, about 15% of heating energy is saved in the winter and about 1% of the cooling energy is saved in winter term. Figure 8 and table 6 show the comparison of results of the field measurements and the simulation. The monthly energy consumption pattern is similar in both case 1 and case 2, despite the 12% error resulting from the comparison of the field measurements and simulation. The error between the results of field measurements and the simulation may appear from difference of weather condition during term of measurement and weather data of simulation program. 66 TBUH 24 October 1~13, Seoul, Korea
Table 5. The monthly energy consumption of ase1, 2 Operating B-Apartment A-Apartment ondition Jan Feb Jun Jul Aug 24h HRV on (ase1) 1565 1448 464 696 95 24h HRV off (ase2) 1896 1663 516 788 998 ase1/asex1(%) 83 87 9 88 91 RA Temp.( ) Total Eff.(%) HRV off(kwh) OA Temp.( ) HRV on(kwh) OA R.H.(%) Energy onsum. [kwh] 25 2 15 1 5 Meas. 24H HRV on Simul. 24h HRV on Meas. 24H HRV off Simul. 24h HRV off 5 4 3 2 1 1 4 7 1 13 16 19 22-1 Hour Fig. 5. The real measured results in certain day of winter term (B-Apartment) 8 7 6 5 4 3 OA Temp.( ) HRV off( 1kwh) OA R.H.(%) HRV on( 1kwh) Total Eff.(%) RA Temp.( ) 2 1 4 7 1 13 16 19 22 Hour Fig. 6. The real measured results in certain day of summer term(a-apartment) Fig. 8. The monthly energy consumption of measurement and simulation Table 6. omparison of monthly energy consumption between field measurement and S/W Simulation Analysis Method Operating B-Apartment A-Apartment ondition Jan Feb Jun Jul Aug 24h HRV on 1565 1448 464 696 95 Field Measurement 24h HRV off 1896 1663 516 788 998 S/W 24h HRV on 1799 1746 528 793 989 Simulation 24h HRV off 212 249 618 824 116 According to the HRV operating schedule under Korean weather conditions, 7 operating schedules were simulated to estimate yearly energy consumption. (Fig. 2) The amount of energy savings can be shown as F-D-B-E--A-G from the top to bottom. Similar result appears in apartment A, B, total heat exchanger and sensible heat exchanger. onsidering yearly energy consumption of apartments A, B in schedule G (HRV turned off 24 hours) and F, the schedule F could reduce energy consumption by 17% in apartment A and 14% in apartment B. 16 Jan Feb Jun Jul Aug Heating ooling Total 14 Energy onsum. [kwh] 2 16 12 8 4 24h HRV on 24h HRV off Energy consum. [kwh] 12 1 8 6 4 2 Jan Feb Jun Jul Aug Schedule A Schedule B Schedule Schedule D Schedule E Schedule F Schedule G Schedule A Schedule B Schedule Schedule D Schedule E Schedule F Schedule G B-Apartment A-Apartment A-Apartment B-Apartment Fig. 7. The monthly energy consumption of ase1, ase2 Fig. 9. The yearly heating and cooling energy consumption TBUH 24 October 1~13, Seoul, Korea 67
3.3 Life ycle ost Analysis The L 2 results of comparison operating schedule G with other schedule in apartment A is shown in table 8. Here, the L 2 was calculated on the basis of initial cost, heating and cooling energy cost, management cost, inflation index 5%, energy cost ascent rate 2.5%. The L 2 can be shown as -A-E-B-D-F from top to bottom. The L analysis result was directly proportioned to operating time. However, HRV could be economical by assuming that HRV effectiveness improves and the energy price shoots up. Table. 8 L result of apartment A Operating schedule L 2 ($) Simple Payback Year(yr) Schedule A 23,781 7 Schedule B 23,46 4 Schedule 23,95 8 Schedule D 23,52 3 Schedule E 23,66 5 Schedule F 22,493 3 Schedule G 24,19-4. onclusions In order to identify the optimal operation schedule, we performed efficiency tests and field measurements of HRV. The results are shown below. 1) The factors we measured were airflow, external/internal leakage, internal exhaust air leakage, pressure drop, temperature and humidity ratio, cross air leakage. 2) The effectiveness of a total heat exchanger and sensible heat exchanger applied to 2 households was measured. Total heat exchange effectiveness has a maximum value when the outdoor temperature is high during the winter season, and at 4 p.m. during the summer. 3) The energy analysis results suggested the optimum operating schedule, which effectively saves energy consumption under Korean weather conditions, considering the effectiveness of HRV and occupants living pattern. Schedule F(HRV turned on for 24 hours) could reduce cooling energy consumption. 4) The result of L analysis including electricity consumption of fan in HRV appears that 24 hour operation of HRV such as schedule F is the most economic in Korea weather condition. References 1) ASHRAE. 1999. Ventilation for Acceptable Indoor Air uality, ANSI/ASHRAE Standard 62-1999, pp. 3-13. 2).G. Barringer, P.E. 1989. Effect of Residential Air-to-Air Heat and Moisture Exchangers on Indoor Humidity, ASHRAE Transactions 1989 PART 1, pp. 464-481. 3) Hoagland, L.. 1986. Moisture transfer characteristics of heat recovery ventilation systems employing rotary materials-winter and summer conditions, Draft of paper presented at BTE onference on Air infiltration. 4) R.. Alexander, P.E. 1992. omparison of Performance Indices for Heat-Recovery Ventilators. ASHRAE Transactions 1992 PART 2, pp. 71-81. 5) W.J. Fisk, P.E. 1985. Formaldehyde and Tracer Gas Transfer between Airstreams in Enthalpy-Type Air-to-Air Heat Exchangers, ASHRAE Transactions 1985 PART 1, pp. 173-185. 6) Y.J. Huang. 1989. DOE-2.1D Data Base of Building Loads for Prototypical Multifamily Buildings in the U.S,. ASHRAE Transactions 1989 PART 2, pp. 786-797. 68 TBUH 24 October 1~13, Seoul, Korea