Policies and Energy Efficiency of Heat Recovery Ventilators in South Korea

Abstract

To reduce national greenhouse gas emissions, the South Korean government has encouraged new energy businesses and implemented policies to reduce energy consumption in buildings, and aims to construct all new buildings as zero-energy buildings by 2025. According to the promotion of policies on passive houses and zero-energy buildings, the thermal insulation and airtight performance of new buildings have been further enhanced. However, to enhance indoor comfort and air quality in new airtight buildings, it is critical to secure an adequate amount of ventilation. Heat recovery ventilators (HRVs) in South Korea have been used for more than 20 years as high-efficiency energy equipment; however, the high-efficiency standard 20 years ago (cooling efficiency 45%, heating efficiency 70%) is still being employed without any change. Most HRVs in the Korean market either meet or exceed this standard. This study examined HRV performance changes from 2010 to 2020 based on the data of 847 HRV performance certifications given by a certification agency. It also analyzed how institutional strategies and related laws contributed to the enhancement of such performance. As HRVs in South Korea are only required to satisfy the pre-defined efficiency criteria, the development and use of HRVs focus more on cost reduction rather than efficiency enhancement. Under such market conditions, it is challenging to research and design highly efficient HRVs along with customer satisfaction. If better market conditions are offered that would welcome HRVs with higher efficiency, the development of better HRVs, as compared to those analyzed in this research study, would be possible.

1. Introduction

To reduce national greenhouse gas emissions, the South Korean government has encouraged new energy businesses and implemented policies to reduce energy consumption in buildings, and aims to construct all new buildings as zero-energy buildings by 2025. According to the promotion of policies on passive houses and zero-energy buildings, the thermal insulation and airtight performance of new buildings have been further enhanced. However, to enhance indoor comfort and air quality in new airtight buildings, it is critical to secure an adequate amount of ventilation. Additionally, as with the prolonged global COVID-19 pandemic, the time spent indoors has increased, and the enhancement of indoor air quality and relevant technologies has been identified as essential for achieving comfort in spaces such as offices, houses, and schools. The indoor air quality directly influences the health of residents, and ventilation is a proactive control approach that eliminates indoor air pollution and enhances indoor comfort [1,2,3].

While an increase in ventilation typically enhances indoor air quality, it also increases the air-conditioning load based on the increase in ventilation [4,5,6,7,8]. As reported by Laverge and Janssens, the heat loss of a well-insulated building due to infiltration and ventilation in mild climate conditions in Europe is approximately 50% of the total heat loss [9]. Thus, ventilation is a crucial energy-control element. A key solution for improving indoor air quality and reducing the air conditioning load in a building is using an energy recovery ventilator (ERV), which recycles heat released in indoor spaces and adequately regulates ventilation. Heat recovery technologies have been efficiently used in Asian and European countries for decades owing to the energy crisis and the impact of new building regulations [10,11,12]. Different studies have analyzed the impact of ERV on energy performance. The effectiveness of indoor heating and cooling energy reduction varies according to regional climatic characteristics, such as the number of days for heating and cooling, outdoor temperature, and humidity, which considerably influence the effectiveness of ERV. Liu et al. [13] demonstrated that with an ERV efficiency of 75% during the heating season in five cities in China, heating energy could be reduced by 20%. Rasouli et al. [14] argued that up to 20% of cooling energy can be saved annually if the ERV is operated under the proposed optimal control. Zhong and Kang [15] reviewed the possibility of ERV application in other climatic regions of China and proposed a type of ERV suitable for each climatic characteristic. Thus, ERV operation, along with an air-conditioning system, requires an effective control approach to reduce energy loss. In high-rise residential buildings, where little-to-no natural infiltration occurs because of sealed building enclosures, a high level of ERV efficiency can be expected from adequate ventilation management. Kim et al. [16] studied the energy contribution of ERV in combined ventilation and air conditioning systems used in a super high-rise residential building and found that a higher energy consumption reduction could be anticipated with a larger temperature deviation in winter than in summer.

In South Korea, various studies have been conducted on heat recovery ventilators (HRVs), and their impact on reducing the air conditioning load has been confirmed. Since the establishment of the Rules on Facility Standards of Buildings [17] in 1992, the ventilation industry in South Korea has developed according to the laws of each department of the South Korean government. HRVs were designated as high-efficiency equipment-certified items in July 1998, and as various problems surrounding indoor air quality surfaced, research in relevant areas was conducted quickly. Between the late 1990s and early 2000s, numerous patents for the development of ventilators were applied and registered; currently, there are fewer such patents, which indicates that the technologies of the internal composition and structure of ventilators have advanced in a convergent manner. The Korea Energy Agency’s (KEA) high-efficiency appliances certification system issues an appliance certificate if the energy efficiency of an appliance satisfies the level set by the KEA and such certified appliances can receive numerous policy benefits. In 2018, HRVs in South Korea were excluded from the list of high-efficiency appliances; however, its minimum performance standards are maintained by the “Health-Friendly Housing Construction Standard” by the Ministry of Land, Infrastructure, and Transport [18], “Rules on Facility Standards of Buildings”, standard KS B 6879 “Heat Exchange Ventilator” [19], “Seoul Green Building design standards” [20], and numerous other regulations and standards. HRVs in South Korea have been used for more than 20 years as high-efficiency energy equipment; however, the high-efficiency standard 20 years ago (cooling efficiency 45%, heating efficiency 70%) is still being employed without any change. Most HRVs in the Korean market either meet or exceed this standard. In the case of general energy facilities, efficiency is improved through material development and product optimization. National policies are also implemented in a way that can continuously improve efficiency. However, in Korea, HRVs are given the same incentives as long as they meet the minimum efficiency requirements. And, in Korea, consumers’ understanding of HRVs is not high, so construction companies are preempting HRVs in multi-family housing. In this situation, most construction companies select and construct the cheapest product among those that meet the lowest efficiency requirements. We would like to analyze the relationship between this institutional situation and the situation in which construction companies have the power to choose products, and how it relates to changes in HRV performance. In Korea, HRVs must obtain performance certification for delivery, and there is an organization that performs such certification. This paper conducted a study based on the performance data of 847 heat recovery ventilators that received performance certification from the author’s accredited certification agency. We analyzed various efficiency-related indicators of HRVs measured by certification agencies and analyzed changes in the performance of heat recovery ventilation devices from 2010 to 2020. By analyzing changes in efficiency by year, we conducted an analysis of how national HRV-related laws and market conditions affect changes in product performance. While general energy facilities improve their efficiency to a certain level every year, it was confirmed that in the case of HRVs, there has been almost no change in efficiency for more than 10 years. Through this analysis, it was confirmed that sufficient technology to improve efficiency has been secured. However, in the current situation, low-priced products have a much greater advantage in the market than high-efficiency products.

Improving the efficiency of HRVs is one of the major energy-saving measures that can reduce the energy consumption of a building, as it reduces heating and cooling energy. In order to reduce energy use in buildings, an institutional mechanism that gives preference to high-efficiency HRVs is needed. This study examined HRV performance changes from 2010 to 2020 based on the data of 847 HRV performance certifications given by a certification agency. It also analyzed how institutional strategies and related laws and regulations affect the performance change of HRVs.

2. Experimental Methods

Figure 1 shows the general shape of the heat recovery ventilator, whose performance changes by year were analyzed in this paper. When outdoor air is introduced, HRVs exchange heat with indoor air to make the temperature and humidity of the introduced outdoor air similar to indoor conditions. The core part responsible for heat exchange in an HRV is the ventilator core, and its general shape is shown in Figure 2.

In South Korea, standard KS B 6879 is used as the standard for HRV testing. The testing approach specified in KS B 6879 was used in this study, and a block diagram of the testing equipment is shown in Figure 3a. The test device consists of two chambers that can, respectively, implement indoor and outdoor environments, and an HRV is installed in the center of the two chambers to evaluate the heat exchange performance of indoor air and outdoor air. Figure 3b shows images of the actual dual chamber, where the temperature was measured using an RTD (Resistance Temperature Detector) sensor and the wind speed was measured using a multi-nozzle fan tester, as shown in Figure 4. In order to perform experiments according to the standard KS B 6879 and evaluate energy efficiency, it is necessary to measure the air volume of the HRV, the power consumption of the HRV, and the temperature and humidity at the HRV inlet and outlet. And, in order to measure effective heat exchange efficiency, considering the amount of air leakage, a CO₂ generator and a CO₂ measuring sensor are required to measure the amount of air leakage.

Table 1. Specifications of the testing facility.

Testing Facility		Specifications	Quantity
Airflow measuring instrument	Multi-nozzle fan tester (3 ea)	Max. 3000 m3/h	Suction side wind tunnel 1ea Blow side wind tunnel 2 ea
	Static pressure differential	Ax.X 1200 Pa
Temperature and humidity measuring instrument	Temperature and humidity	OMEGA (PT100) (−20~80) °C	2 ea per SA (Supply air), RA (Return air), OA (Outdoor air), EA (Exhaust air)
	Recorder	YOKOGAWA (MX100)	1 ea
Power measuring instrument	Digital Power Meter	YOKOGAWA (WT330)	1 ea
CO2 emission and measurement	CO2 measuring sensor	VAISALA (GMT222)	1 ea per SA, RA, OA, EA
	CO2 generator	(0~10,000) ppm	1 ea

lists the specifications of the individual sensors and testing facility.

The HRV efficiency was examined based on the heating and cooling test conditions as per KS B 6879, as shown in

Table 2. Air conditions in cooling and heating tests in the KS B 6879 (2020).

Parameter	Temperature of Return Air (°C)		Temperature of Outside Air (°C)
	Dry-Bulb	Wet-Bulb	Dry-Bulb	Wet-Bulb
Cooling	24 ± 0.3	17 ± 0.2	35 ± 0.3	24 ± 0.2
Heating	22 ± 0.3	13.9 ± 0.2	2 ± 0.3	0.4 ± 0.2

Note: Enthalpy in the cooling cycles: Indoor 11.37 kcal/kg, Outdoor 17.13 kcal/kg. Enthalpy in the heating cycles: Indoor 9.27 kcal/kg, Outdoor 2.44 kcal/kg.

.

In KS B 6879, the sensible heat exchange efficiency and total heat exchange efficiency are defined as shown in Equations (1) and (2), respectively. To derive the sensible heat exchange efficiency, see Figure 3. The dry temperature of the outdoor air, supply air, and return air points in 3(a) must be measured. Sensible heat exchange efficiency is obtained as shown in Equation (1) through the dry bulb temperature at three points. To derive the total heat exchange efficiency, enthalpy must be measured at the same three points as when calculating the sensible heat exchange efficiency. Enthalpy is obtained from the measured dry temperature and wet-bulb temperature.

Through enthalpy at three points, the total heat exchange efficiency is obtained as shown in Equation (2). The air leakage rate determines the amount of air leakage by supplying a high concentration of carbon dioxide to the return air and measuring the change in carbon dioxide concentration in outdoor air and supply air due to leakage. Carbon dioxide concentration was measured by installing carbon dioxide sensors in three locations: outdoor air, supply air, and return air ducts. The air leakage rate is defined using the following equation as the amount of air leakage divided by the air supply amount. Equations (3) and (4) were used to determine the leakage rate and leakage ratio, respectively. Effective heat exchange efficiency considering the amount of leakage is obtained from the relationship between total heat exchange efficiency and leakage ratio. Equation (5) was used to calculate the effective heat exchange efficiency. Equation (6) was used to calculate the energy coefficient, which is a dimensionless ratio of the amount of energy reduction and the power consumed by the blower.

$${\eta }_s=\frac{T_{OA}-T_{SA}}{T_{OA}-T_{RA}}\times 100$$

(1)

$${\eta }_t=\frac{I_{OA}-I_{SA}}{I_{OA}-I_{RA}}\times 100$$

(2)

$$q=Q_S\times \frac{E_G}{100}$$

(3)

$${\eta }_q=\frac{q}{Q_S}\times 100$$

(4)

$${\eta }_e=\frac{{\eta }_t-{\eta }_q}{100-{\eta }_q}\times 100$$

(5)

$$\mathrm{C}\mathrm{O}\mathrm{E}=\frac{\rho {\eta }_e{Q}_E\left|I_{OA}\right.-\left.I_{RA}\right|}{W}$$

(6)

In contrast to other energy-saving building facilities in South Korea, HRVs provide similar advantages only if it passes the efficiency threshold. Furthermore, as demonstrated in

Table 3. Change in the high-efficiency standard threshold.

	Before 2010	From 2010
Effective total heat exchange efficiency (Cooling)	45%	45%
Effective total heat exchange efficiency (Heating)	70%	70%
Coefficient of energy (Cooling)	5	8
Coefficient of energy (Heating)	10	15

, the high-efficiency threshold was revised in 2010 and continues to be maintained with little-to-no change.

Awareness and use of HRVs in South Korea is still uncommon; hence, as building contractors choose HRVs and apply them to high-rise residential buildings, they select the cheapest product that satisfies such a threshold rather than selecting ones with better performance.

3. Results

KS B 6879 classifies HRVs into small, medium, and large sizes based on the specified amount of wind as shown in

Table 4. Classification based on a specified amount of wind (KS B 6879).

Classification	Small	Medium	Large
Amount of wind	At or below 300 m3/h	Exceeding 300 m3/h, at or below 1000 m3/h	Exceeding 1000 m3/h, at or below 3000 m3/h

. In this study, we analyzed small- and medium-sized HRVs used in South Korea.

The ventilator core is a component where heat exchange takes place, and there is a strong correlation between the size of the ventilator core and HRV efficiency. And, as the time the air stays inside the ventilator core increases (the smaller the air volume compared to the size of the ventilator core), the heat exchange efficiency of HRVs increase. To determine whether the change in efficiency is simply due to the size of the device, we summarized the value obtained by dividing the experimental air volume by the size of the ventilator core. Figure 5 shows the size of the ventilator cores employed in 847 HRVs tested for certification between 2010 and 2020, divided by the amount of wind used in the test. Figure 6 shows year-wise size of the HRVs divided by the amount of wind used in the test. These graphs demonstrate large maximum and minimum gaps between the volumes of products and cores. There was no change in the size of the ventilator cores and HRVs until 2018, and from 2019 onward, it increased. This is because of the additional modules required to satisfy consumer demands for additional functions of HRVs (such as air purification, and condensation prevention). Furthermore, as shown in Figure 7, the bypass function and the enhancement of filter performance in HRVs have become mandatory, and air purification has been applied to the inner return mode. The overall flow path became complex, and the internal pressure reduction increased because of these additional functions. Since 2020, the size of the cores has increased to maintain the total pressure reduction at a specific level.

Figure 8 and Figure 9 show the year-wise changes in the in sensible heat exchange efficiency of HRVs. In HRVs, the thickness of the ventilator cores is a crucial factor for sensible heat exchange efficiency, and since 2010, the weight of the ventilator core in South Korea has been maintained at 28–29 g/m². Therefore, the sensible heat exchange efficiency was maintained at a specific level without significant changes. The heating efficiency was higher than the cooling efficiency, as shown in Figure 8 and Figure 9. This is because of higher indoor and outdoor temperature differences in heating than those in cooling, as shown in Table 2.

Figure 10 and Figure 11 show the year-wise changes in the total heat exchange efficiency of the HRV. Under heating conditions, no change in the total heat exchange efficiency has been made since 2010. However, there was a significant increase in heat exchange efficiency under cooling conditions in 2016. Until 2015, most companies had used ventilator cores from Japanese base paper; however, in 2016, they began using newly designed base papers in South Korea. Owing to the enhanced moisture absorption performance of these ventilator cores, the efficiency under cooling conditions has increased considerably. Despite the above, South Korea’s HRV policies are one of the primary reasons for the little-to-no change in heating efficiency. Most products that satisfy a heating efficiency of 70% usually meet a cooling efficiency of 45% during the cooling and heating temperature and humidity tests. Once these products meet the minimum efficiency of 70% for heating and 45% for cooling, companies choose the least expensive HRVs among them. Accordingly, most studies and developments have focused on satisfying a heating efficiency of 70%. Thus, once the heat exchange efficiency for heating increases because of the enhancement in ventilator cores performance, companies tend to develop HRVs by reducing the size of ventilator cores or the number of HRV components to save cost while meeting the heat exchange efficiency of 70%. While both heating and cooling efficiencies increased owing to the enhancement of ventilator core performance, a cost-reducing design that only satisfied the minimum standards increased the cooling efficiency while maintaining the heating efficiency at 70%.

Figure 12 shows year-wise changes in the leakage rate of HRVs. Figure 13 and Figure 14 show the year-wise changes in the effective total heat exchange efficiency of HRVs. Effective total heat exchange efficiency reflects the leakage rate of the heat-exchange unit, as shown in Equation (5). The leakage rate technology standards for HRVs in South Korea are at or below 10%, and the average leakage rate of the 847 HRVs tested between 2010 and 2020 was nearly constant at approximately 2.5–4%. As the HRV leakage rate deviation was insignificant, the year-wise effective total heat exchange efficiency had similar trends for total heat exchange efficiency.

Figure 15 and Figure 16 show the year-wise changes in the coefficient of energy of the HRV. Until 2010, the coefficient of energy standards in South Korea was maintained at five for cooling and ten for heating, and since 2011, they have been at 8 for cooling and 15 for heating. Since 2010, the development and implementation of brushless direct current (BLDC) fan motors have resulted in a consistent increase in the coefficient of energy. While additional technical advancements were possible, most HRV companies started to miniaturize the BLDC fan motor to reduce costs. Since 2016, different cost-reducing designs have been stabilized and the coefficient of energy has remained constant. Several South Korean companies can design HRVs with high coefficient of energy levels. However, the country’s policy enforces the lowest bidding, and, therefore, many see no need for either technical development or the use of high-efficiency products with the implementation of high-efficiency parts. The HRV market in South Korea is dominated by low-cost products, whereas most energy facilities encourage high-efficiency products.

4. Conclusions

There has been continuous research and development of all the structures and facilities, including windows, doors, walls, and HVAC equipment, among others, that can save energy costs in buildings in South Korea, and corresponding policy support has been provided for high-efficiency facilities. According to market and national policies, balanced consideration is given to performance enhancement and cost reduction in technological development. In addition, as reported by previous studies, the impact of ventilation on the energy consumption of buildings is considerable. While numerous technologies have been designed to enhance the performance of HRVs, such as the application of a high-efficiency BLDC motor or the development of a new base paper, the efficiency of HRVs in the South Korean market has been stagnant without substantial change over the past decades because of the market’s preference for cost reduction as shown in the Figure 8, Figure 9, Figure 10, Figure 11, Figure 12, Figure 13, Figure 14, Figure 15 and Figure 16. The enhancement of ventilator efficiency is critical for reducing energy consumption in buildings in compliance with the country’s energy policy. To enhance the efficiency of HRVs in South Korea, company efforts are crucial; however, simultaneously, high-efficiency HRVs should be accepted in the market. Nevertheless, the current policy direction focuses only on cost-saving competition, making it challenging for high-efficiency HRVs to compete in the market. HRVs in South Korea are used in new buildings to satisfy permission standards and are chosen by building contractors. Thus, price, not efficiency, is the key to product selection. In addition, manufacturers focus on developing cost-saving products rather than enhancing their efficiency.

High-efficiency HRVs can play a significant role in reducing the cooling and heating energy requirements and greenhouse gas emissions. However, because of cost-saving competition, contractors cannot proactively enhance HRVs for consumers, and currently, HRVs are considered auxiliary equipment provided by the builders and are not extensively used in each household. Higher energy consumption reduction using HRVs requires proper use and regular maintenance. However, the use of HRVs in South Korea is very low. While numerous HRVs are installed in South Korea, the ratio of consumers who willingly choose the installation of HRVs is extremely low, as is the ratio of those who use the HRV correctly. As HRVs in South Korea are only required to satisfy the pre-defined efficiency criteria, the development and use of HRVs focus more on cost reduction as compared to efficiency enhancement. Under such market conditions, it is challenging to research and design highly efficient HRVs along with customer satisfaction. If better market conditions are offered that would welcome HRVs with higher efficiency, the development of better HRVs, as compared to those analyzed in this research study, would be possible.