Operational performance evaluation of a Passive house residential building in northern China based on long-term monitoring in winter

Abstract

Passive houses, called nearly zero energy buildings in China, are developing rapidly. These constructions in China are mainly located in cold climate zones. Due to highly efficient energy-saving technology, Passive houses can decrease space heating demand (SHD) by 70%–90% compared to local conventional buildings. However, this energy-saving rate is still a theoretical result and needs to be verified by real data. There is a lack of studies evaluating the performance of residential Passive houses through monitored data in China. This article selects a newly built multi-storey residential Passive house building in Qingdao to accurately quantify its energy performance. Through energy consumption monitoring throughout winter, the average SHD of this building at an occupancy rate of 47% was found to be 28 kWh/(m²·a) and the primary energy consumption was 96.7 kWh/(m²·a), while maintaining a high level of indoor comfort. Compared with local conventional Green Buildings, the SHD of the case building was reduced by 86.3% and the total energy consumption was reduced by 69.2%. The results demonstrate that Passive houses have a great energy-saving potential and provide evidence supporting the use of Passive houses as an option for sustainable building in northern China.

Keywords

Passive house Energy performance Monitoring Space heating Comfortable indoor environment

Introduction

The 2021 global status report for buildings and construction pointed out that the construction industry accounted for 36% of global end-use energy consumption and 37% of energy-related CO₂ emissions in 2020.¹ A report by the Ministry of Housing and Urban-Rural Development of China (MoHURD)² revealed that the direct and indirect carbon emissions of China’s construction sector account for about 40% of total societal carbon emissions. To achieve the ‘Carbon emissions peak before 2030 and carbon neutrality before 2060’ targets,³ the General Office of the Central Committee of the Communist Party of China and the General Office of the State Council⁴ have called for the promotion of passive ultra-low-energy buildings (PUEBs) and nearly zero energy buildings (nZEBs),^5,6 and a focus on building operation energy efficiency. PUEBs are the primary form of nZEBs. Both have the same indoor environmental parameters; however, the energy efficiency of PUEBs is slightly lower than that of nZEBs. It is foreseeable that there will be huge developments in Passive houses (PHs) or nZEBs during the following five-year (14^th Five-Year Plan) period in China.

Throughout the 13^th Five-Year Plan period, China built more than 10 million m² of PUEBs, mostly located in cold climate zones.⁷ Based on these projects, a batch of energy-saving design and evaluation standards of PUEBs have been issued one after another.^8,9 The energy performance of some public PH projects has been monitored and evaluated, such as the PHTEC in Qingdao^10,11 and an office building in Zhuozhou, Hebei.¹² There are also other monitored public nZEB projects in severely cold zones¹³ and in hot summer and warm winter climate regions¹⁴ in China. However, the operating energy performance of residential PH buildings has not been evaluated or published. There are currently no case studies or literature on the monitoring of residential PH buildings in China.¹⁵

In contrast, there are numerous cases of monitored PHs, such as single-family PHs,¹⁶ low-energy houses¹⁷ and multiple-family PHs,¹⁸ in other countries. These authors studied primary energy (PE) consumption, space heating demand (SHD), indoor air quality (IAQ), etc. Table 1 summarizes some relevant research from recent years.

Table 1.

Summary of relevant research from monitored buildings.

Authors	Years of research	Locations	Research aims	Outcomes
Ridley et al.¹⁶	2010–2012	London, UK	Monitoring of the performance of the first new dwelling certified to the PH standard	■ Demanded space heating of 12.1 kWh/m² less than the criteria of 15 kWh/m².
				■ The annual PE demand is 125 kWh/m², slightly higher than the goal of 120 kWh/m².
				■ The measured internal heat gain (IHG) was 3.65 W/m², much larger than the 2.1 W/m² in residential PHs.
				■ Total energy consumption of 65 kWh/m².
				■ Passive House Planning Package (PHPP) could precisely predict SHD and overheating.
				■ Users’ behaviour could greatly affect SHD.
Fokaides et al.¹⁴	2014–2015	Cyprus	Monitoring of the performance of the first PH in Cyprus to investigate the discrepancies between design and operation	■ Optimized night ventilation could lower the indoor air temperature by 1.4°C on average.
Fokaides et al.¹⁴	2014–2015	Cyprus		■ An increase in the cooling capacity of heating ventilation and air conditioning (HVAC) could improve thermal performance.
Dar et al.¹⁹	2014	Oslo, Norway	Identification of the parameters of occupant-related heat gain in a well-insulated detached house: occupant’s behaviour, appliance usage and family size	■ Occupancy patterns and family size were major parameters to explain the difference between actual and simulated energy use in buildings.
Dar et al.¹⁹	2014	Oslo, Norway		■ Occupant’s behaviour regarding SHD compared to domestic hot water (DHW) greatly influenced the performance of heat pumps.
Guerra-Santin et al.²⁰	2012	UK	Investigation of expected and actual performance in low-energy buildings	■ The predicted performance did not match their actual performance. The reasons were the occupant’s behaviour and poor construction quality.
Dermentzis et al.²¹	2016–2019	Innsbruck, Austria	Monitoring of two multi-family houses to investigate if they reached net-zero energy standards	■ The generated photovoltaic (PV) electricity was 6% higher than the electricity consumption of heat pumps on average during 4 years.
				■ The generated electricity could not cover all consumption of building systems, appliances and auxiliaries.
				■ Reducing heating losses and improving electricity efficiency were important methods for net-zero energy buildings.
Peper et al.²²	1997–2015	Germany	Research and monitoring of many newly built and retrofit PH projects	■ The heating demand is around 15 kWh/(m²•a), which is supported by an abundance of actual data.
Mihai et al.²³	2014–2015	Bucharest, Romania	Investigation of the performance of an energy system designed for PH	■ Heating demand is close to 13 kWh/(m²•a) and its indoor environment maintained comfortable conditions.
Mihai et al.²³	2014–2015	Bucharest, Romania		■ Earth-air heat exchange technology and PV to reduce the share of non-renewable PE.
Rojas et al.²⁴	2009–2011	Kufstein and Innsbruck, Austria	Monitoring and socio-scientific surveys to investigate the IAQ and end-user satisfaction in social PH dwellings	■ The average indoor temperatures in winter were much higher than the documented PHs.
				■ Over-heating in summer was a highlighted problem, especially on the top floor of the apartment. Sun shading could provide a solution.
				■ Housing attained a high level of satisfaction according to the feedback of the occupants.

Ridley et al.¹⁶ and Mihai et al.²³ evaluated the operating performance of PHs in the UK and Romania, respectively. They monitored SHD, PE consumption, IAQ, etc., and found that the indoor environment was comfortable and in line with the design indicators, but users’ behaviour had an impact on energy consumption resulting in PE consumption exceeding the target value. Dar et al.¹⁹ and Guerra-Santin et al.²⁰ monitored the operating energy consumption of low-energy buildings in Norway and the UK, respectively. They found that there was a difference between actual and simulated energy consumption in buildings; the occupant’s behaviour and construction quality were the main causes for this difference. Peper et al.²² evaluated many PHs in Germany and found that the SHD was around 15 kWh/(m²•a). Dermentzis et al.²¹ and Mihai et al.²³ also proposed that improving the efficiency of electricity consumption and utilizing renewable energy were ways to improve the energy efficiency of buildings. The above analyses have illustrated that during the evaluation of building operating performance certain factors would need to be considered, like the quality of design and construction, users’ behaviour and family size.

The goal of this case study is to verify whether the operation of this residential PH building in a cold climate zone meets the expectation of energy-saving, including electricity consumption, SHD and corresponding indoor environment quality (IEQ). This article focuses on the first multi-storey residential PH building in China to implement energy consumption monitoring, which can provide meaningful support for policymakers in China. The novelty lies in (a) a calculation model based on the HVAC system of this building and (b) the establishment of an energy consumption monitoring system according to the calculation model. In addition, the verification of the accuracy of simulation tools is executed by the comparison of monitored data and simulated data.

Methodology

This article presents monitoring results of a residential PH building, focusing on its SHD, electricity consumption and site energy consumption. The energy efficiency level of this PH building was evaluated by comparing the monitored data with the simulated data of simulation tools Passive House Planning Package (PHPP) and IBE (IBE is a PUEB evaluation software based on China’s national conditions⁶ and ISO 13790 standards.) and comparing it with the actual energy consumption of a neighbouring Green Building (GB) (see Figure 1).

Figure 1.

Flowchart of methodology.

Basic information on the investigated building

Qingdao is a coastal city in northern China. The summer in Qingdao is hot and humid. The hottest month is August, with an average daily temperature of 25°C, so active cooling and dehumidification are necessary to maintain a comfortable indoor environment. The winter is cold. The coldest month is January, with an average daily temperature of −2°C, and space heating in the winter is a national requirement.²⁵ During spring and autumn, natural ventilation can provide a comfortable indoor environment. Even so, sudden weather changes do occur at any time. For example, cold fronts with strong winds occurred from 6^th to 7^th January 2021. The lowest temperature in Qingdao’s urban area on the 7^th January was −15.9°C, which was the lowest temperature monitored by the Qingdao weather station since 1961.²⁶

A PH district²⁵ was constructed in 2019 that has been certified by the German Passive House Institute (PHI),²⁷ and also certified as a two-star GB by China GB Council.²⁸ A PH is a building in which thermal comfort can be guaranteed by post-heating or post-cooling the incoming fresh-air mass required for good IAQ.²⁹ The Chinese Standard, GB/T 50378-2019, refers to the buildings, which save resources, protect the environment, reduce pollution and provide people with healthy, suitable and efficient spaces as much as possible throughout the building’s life cycle.³⁰ The PH building No. 2 with 3 units and 36 apartments is one of the buildings in this district (Figures 2 and 3). Ground source heat pumps (GSHPs) and PV are used in this district as renewable energy (Figure 2). The basic building dimensions are given in Table 2. For comparison, a building from an adjacent two-star GB district built in 2016 was selected²⁵ (see Figure 3(d)). The PH and GB districts and buildings were introduced in detail in previous publications.²⁵ The details of GB are not included herein.

Figure 2.

Section drawing of PH building no. 2. The outer yellow line is the building envelope and the inner red line is the airtight layer. On the roof, PV is installed and there are GSHP service rooms in the basement.

Figure 3.

Photos of PH and GB buildings.

Table 2.

Information on PH building no. 2.

Parameter	Value
Gross floor area [m²]	5539
Treated floor area (TFA) [m²]	4244.4
Gross volume [m³]	10,990
Surface area [m²]	3077
Surface to volume ratio	0.28
Window to wall ratio (east)	0.09
Window to wall ratio (south)	0.38
Window to wall ratio (west)	0.09
Window to wall ratio (north)	0.24
Gross height [m]	21.6
Floors above ground	7
PV [kWp]	12.4
Mechanical ventilation with heat recovery (MVHR) (compact device) (CD) [unit]	36

The PH building has a compact shape that contributes to minimizing heat transfer through the building envelope. The thermal-physical properties of the building envelope are given in Table 3. Balconies that protrude out of the envelope are treated to break thermal bridges (TBs). The parts of the building envelope where the heat flow density increases significantly are known as TBs. The impact of TBs on the energy consumption of PH is very significant. The PH should strictly control the appearance of TBs and design the building envelope to limit TBs.

Table 3.

Thermal-physical properties of the building envelope.

Items	Designed value	Required value by GB code	Description
Wall	0.15 W/m²K	0.64 W/m²K	230 mm graphite expanded polystyrene, λ = 0.035 W/mK
Roof	0.10 W/m²K	0.4 W/m²K	300 mm extruded polystyrene, λ = 0.032 W/mK
Floor slab	0.17 W/m²K	0.6 W/m²K	250 mm mineral wool, λ = 0.044 W/mK
Window	0.8 W/m²K	2.0 W/m²K	Triple panes, double low-E
Solar heat gain coefficient (SHGC)	0.57	0.76	—
Shading system	External aluminium alloy blinds	No requirement	—
Airtightness (n₅₀)	0.53	No requirement	—

The PH building’s energy consumption was simulated via PHPP,³¹ which guided the entire period of design and construction. PHPP is an EXCEL table-based software for calculating the energy consumption of PH buildings. It can provide the following results reliably: annual heating demand and maximum heating load, annual cooling demand and maximum cooling load (in case of active cooling); comfort level during summer (frequency of overheating); annual demand for renewable PE and PE demand of all energy services in the entire building; assessment of the annual renewable energy gains.^32,33 First of all, compared with the scattered and short duration of cooling demand of customers in summer, the heating demand is more constant and concentrated in winter, and the energy-saving and carbon-reducing effect is more obvious. In addition, heating demand is the most important indicator of PH, so this article covers the monitored project in winter and is compared with the simulated indicators in winter, while the summer indicators, such as the cooling demand and frequency of overheating, are not the primary focus of this article.

The compact device (CD) includes mechanical ventilation with heat recovery (MVHR) that provides continuous fresh air into the building and a GSHP that provides space heating in winter, space cooling in summer and DHW. The characteristics of the two types of CDs are specified in Table 4. Out of the 36 apartments, 34 use type 1 CDs and 2 use type 2 CDs. All the heat pumps in the CDs are equipped with variable speed compressors to change the flow rate according to cooling and heating loads. The ground water is centrally distributed to each CD in the apartment and used as a source for the heat pump.

Table 4.

Main information about the compact devices.

Parameters	Unit	Type
Model	Unit	Type 1	Type 2
Rated cooling capacity	kW	3.5	5.5
Rated heating capacity	kW	3.7	5.8
Heat recovery coefficient	%	80.0	75.0
Enthalpy recovery coefficient at cooling	%	74.0	68.0
Total supply airflow rate	m³/h	500	750
Return airflow rate	m³/h	350	550
Fresh airflow rate	m³/h	150	200
External static pressure	Pa	150	200
Exhaust airflow rate	m³/h	200	300
Power source	V/Hz	220∼/50	220∼/50
EER at cooling	kW/kW	4.86	5.29
COP at heating	kW/kW	4.52	4.46
Direct hot water supply rate	L/min	4.0	5.0
Dimensions	mm	585 × 600 × 1620	705 × 700 × 1670
Airtightness	%	2.0	2.0
Frost protection	—	Electric pre-heater

Figure 4 depicts the location and airflow organization of the CDs in two typical apartments. In the left apartment, the CD is positioned on the northern exterior balcony, which is outside of the building envelope. In the apartment on the right, the CD is placed in the kitchen, which is within the building envelope. The circulation air as well as the supply air is conditioned to provide space heating and cooling.

Figure 4.

Two typical floor layouts and airflow organization. The CDs are rationally positioned. Orange dots are sensors for IEQ monitoring.

Monitoring system setup

The components of the monitoring system are listed in Table 5. Two electricity meters are installed in each household, one only measures the electricity consumption of the CD, marked as W_CD (including the electricity consumption of a heat pump, fans, a small water pump for the DHW and a control system), and the other measures total electricity consumption of the apartment. The difference between the two electricity meters is the electricity consumption of households (including electrical appliances, lighting, sockets, etc. as well as the electrical heater in the hot water tank (WT)). The CD in each apartment receives subsoil heat, which is transported by water pumps in the service rooms on the second basement floor. Two heat meters are installed in the water supply and return pipes to measure the heat supplied to the CD and WT, respectively (see Figure 5). Electricity, heat meters and IEQ sensors are monitored at a frequency of 5 minutes. All meters and IEQ sensors use MODBUS Remote Terminal Unit (RTU) as protocol. The monitoring system started in December 2020, and the data was collected and analyzed in the winter of 2021 after 1 year of trial operation.

Table 5.

Meters and sensors adopted in the monitoring system.

Name	Number	Type	Description
Heat meter type 1 (HMT1)	6	DN50	Ground source side main heating meter
Heat meter type 2 (HMT2)	36	DN20	Indoor CD side heating meter
Heat meter type 3 (HMT3)	36	DN25	Ground source side indoor heating meter
Electricity meters for CD	36	DDSD1352	CD electricity consumption (220 V)
In-home electricity meters	36	DDSD1352	Apartment electricity consumption
CO₂ concentration sensors	1	CM 1106	In each apartment
Relative humidity sensors	5	SHT3x-DIS	In each apartment, accuracy ±2%
Temperature sensors	5	SHT3x-DIS	In each apartment, accuracy ±0.3 K
Electricity meters for lifts	3	380 V	Elevator electricity consumption
Electricity meter for building	1	380 V	Building total electricity consumption
WP electricity meters	3	380 V	Water pump electricity consumption
Lighting meters in public areas	3	380 V	Lighting electricity consumption

Figure 5.

Schematic diagram of energy balance in a CD.

Each apartment has 5 SHT3x-DIS IEQ sensors, shown as orange dots in Figure 4. The accuracy of the main sensor is ± 0.3 K of temperature and ±2% of relative humidity. The heat meters have a relative uncertainty of 2% for volume flow measurements, and the electricity meters selected have a 1% relative uncertainty. If the main sensor fails during measurement, the average value of the other four sensors will be used as the IEQ of the apartment.

A weather station was installed on a neighbouring building’s roof to obtain outdoor climate information, including temperature, relative humidity and solar radiation. Each apartment has a data collector that can communicate with the building energy management system (BEMS) through fieldbuses to transmit IEQ data.

From Figure 5, the CD input energy includes subsoil heat (marked as Q_GSHP) and electricity (W_CD). The energy generated by the CD is divided into three main parts: the first part heats the DHW (marked as Q_DHW) to ensure that the household has hot water for bathing and washing. The second part heats the supply air (marked as Q_SH) that comes out from the heat exchanger for the space heating. The last part is distributed to the apartment by the CD itself as heat loss (marked as Q_Loss); however, the proportion of this part, including conversion loss, distribution loss and storage loss, is very low and difficult to measure. From another perspective, the heat losses are within the envelope and indirectly heat the apartment, so they can be considered negligible.

According to the law of conservation of energy, the energy input on the left is equal to the energy output on the right, as in equation (1):

Q_{G S H P} + W_{C D} = Q_{D H W} + Q_{S H} + Q_{L o s s}

(1)

where Q_GSHP is the subsoil heat; W_CD is the electricity for the CD, [kWh]; Q_DHW is the heat for the DHW, [kWh]; Q_SH is the heat for space heating, [kWh] and Q_Loss is the heat loss from the CD; here, it can be seen as zero, [kWh].

From equation (1) above, the SHD can be calculated via the three datasets (Q_GSHP, W_CD and Q_DHW) derived from monitoring.

The trial monitoring and commissioning of the system were carried out in the winter of 2020–2021. At that time, the building’s occupancy rate was very low, only a few of the 36 apartments were occupied and the data deviation was large. Hence, the monitored data from 1^st Nov. 2021 to 31^st Mar. 2022 were used as the data for the case study. In addition, the measured SHD and IEQ were analyzed by this study according to the area-weighted average method.

During the monitored winter, only 17 of the 36 apartments were inhabited. To enhance the plausibility of the monitoring campaign, the CDs in the 12 uninhabited apartments were switched on to provide space heating. In this way, the case building can achieve the equivalent of an occupancy rate of 80%. These 29 apartments were randomly distributed in the building. The remaining seven apartments were not allowed to be monitored by the owners and they were mainly empty during the monitoring period, although many sensors were already installed in them (see Table 6).

Table 6.

Distribution of the monitored inhabited and heated apartments.

Apartments that are	Unit 1	Unit 2	Unit 3	Whole buildings
Monitored, inhabited and heated	5	7	5	17
Monitored, not inhabited and heated	2	5	5	12
Not monitored, not inhabited and not heated	5	0	2	7^a
Total number of apartments	12	12	12	36

^aRemark 1: 2 out of 7 were partly inhabited for a couple of months, not the entire winter.

Results

Space heating demand

The measured energy consumption for SHD of the 29 apartments in this PH building is shown in Figure 6. The treated floor area (TFA) of these 29 apartments was 3202.8 m², and the average SHD accounted for 28 kWh/(m²·a). However, 12 of the 29 apartments were not occupied but heated, and 7 empty apartments have influenced the rest.

Figure 6.

The space heating demand of 29 apartments in the winter.

As previously stated, this building has a total of 36 apartments, which are evenly distributed into 3 units. The middle unit, ‘unit 2’, includes 12 apartments, of which 7 apartments are occupied and 5 apartments are unoccupied, but heated by CDs after obtaining the permission of the owners (see Table 6). So, this unit can be seen as a PH building with smaller dimensions, which has the same building envelope and HVAC system as the monitored PH building. The energy consumption for monthly SHD in unit 2 is shown in Figure 7. The average SHD accounts for 19.7 kWh/(m²·a) based on the TFA that includes the staircase as in PH design, which is 4.7 kWh/(m²·a) more than 15 kWh/(m²·a) of the PH standard. The ‘small PH building’ unit 2 has a better energy performance than the whole building.

Figure 7.

Monthly average space heating demand of unit 2.

To measure the IHG of this building, an experiment was performed. Ten apartments were selected and divided into two groups, and the indoor temperature was set to 24°C at the same time. The inhabited five apartments belong to group A and the non-inhabited five apartments that were heated by the CDs to group B. The monitoring lasted for 8 days, and then the average temperatures, electricity consumption and SHD of the two groups were compared (see Table 7).

Table 7.

Monitored results of 10 apartments for 8 days.

Group	No.	TFA [m²]	Ave. Temp. [°C]	Total SHD [kWh/m²]
A	A1	108.3	23.4	2.8
	A2	106.1	23.5	0.1
	A3	106.2	23.7	0.84
	A4	106.1	22.2	0.7
	A5	108.4	22.8	0.1
B	B1	106.1	22.7	1.8
	B2	96.5	23.0	2.44
	B3	106.1	24.2	1.12
	B4	106.1	21.9	2.16
	B5	136	24.2	1.89

The results of the 8 days of data show that the average temperature of group A was 23.1°C, and the average SHD was 0.11 kWh/m². The average temperature of group B was 23.3°C, and the average SHD was 0.23 kWh/m². So, the SHD of group A was 0.12 kWh/m² less than that of group B, and the temperature of group B was 0.2°C higher than that of group A. If the temperature difference per degree brings 2 kWh/m² of additional energy consumption,³⁴ after adjustment, the result is approximately equal to 2.9 W/m² when the values are input in equation (2). Thus, 2.9 W/m² is the average IHG (Q_IHG) of group A.

Q_{I H G} = \frac{[Q_{b -} {(T b - T a)}_{*} \frac{2}{d} - Q a] * 1000}{24}

(2)

where Q_IHG is the internal heat gain [W/m²], Q_a and Q_b are the SHD of groups a and b [kWh/m²], T_a and T_b are the average temperatures of groups a and b [°C] and d is the days of monitoring, [-].

This monitored IHG of 2.9 W/m² is close to the recommended value of 2.1 W/m² and within the scale of 2.1–4.1 W/m².³⁵ To verify the reason for excessive IHG, the living conditions of families in group A, collected by questionnaire survey, are shown in Table 8. Since most Chinese families live with the elderly and cook three times per day, this was established as the main reason why the IHG is greater than the recommended value.

Table 8.

The living conditions of the five families obtained through a questionnaire.

Apartment	Family size (people) and age range		Space heating in the winter	Status of residency
1	4	2 over 60	On	Long-term
1	4	2 from 18 to 60	On	Long-term
2	5	2 over 60	On	Long-term
		2 from 18 to 60
		1 under 18
3	5	2 over 60	On	Long-term
		2 from 18 to 60
		1 under 18
4	2	2 from 18 to 60	On	Long-term
5	3	2 from 18 to 60	On	Long-term
5	3	1 under 18	On	Long-term

From the monitored data in the winter, the average electricity consumption of the 17 apartments that were inhabited was 24.7 kWh/m², and the average electricity consumption of the 12 apartments that were not occupied was 15.9 kWh/m², which was 8.8 kWh/m² less than the electricity consumption of the occupied apartments. This difference reflects the level of the electricity demand of households, aside from the electricity consumption of CD (see Figure 8).

Figure 8.

The average electricity consumption of 29 households, charts on the left for the 17 inhabited apartments and charts on the right for the non-inhabited 12 apartments.

Indoor environment quality

The monitored indoor air temperature and relative humidity of 29 apartments in this building in the winter are shown in Table 9 and Figure 9.

Table 9.

The measured interior environment of PH building.

No.	Interior environment	PH building	Unit 2
1	Average air temperature [°C]	21.9	21.4
2	Maximum air temperature [°C]	23.5	23.6
3	Lowest air temperature [°C]	16.6	16.6
4	Average relative humidity [-]	37.2%	37.7%
5	Maximum relative humidity [-]	48.9%	48.9%
6	Lowest relative humidity [-]	29%	32.2%
7	Average CO₂ concentration [ppm]	502	507

Figure 9.

The interior environment of the 29 apartments in the winter: (a) the average indoor air temperature, (b) the average indoor relative humidity and (c) the cumulative distribution function (CDF) of the indoor CO₂ concentration in 17 inhabited apartments.

In general, the indoor relative humidity during the winter varied from 30% to 60% and the indoor air temperature stayed in a comfortable zone in this PH building. However, compared with the IEQ in Table 9, the outdoor temperature and relative humidity show big fluctuations. The maximum outdoor temperature peaked at 17.2°C in November and the lowest was −6.1°C in December. The average outdoor temperature in the winter was 4.5°C. The outdoor relative humidity was from 28% to 95% and the average relative humidity was 63% in the winter. Figure 9(c) shows the cumulative distribution function (CDF) of the indoor CO₂ concentration in 17 apartments. The CO₂ concentration was mainly under 800 ppm and only above 1000 ppm 6% of the time.

Electricity, natural gas and domestic hot water consumption

The electricity monitoring of this PH building was performed from April 2021 to March 2022, for a total of 1 year. The accumulative electricity consumption was 191,822 kWh, including 158,040 kWh for households, 4668 kWh for the lighting of public spaces like staircases, 6257 kWh for elevators and 22,857 kWh for water pumps in the service rooms, all of which are electricity input within the building envelope (see Figure 10). The results show the household electricity consumption (including CD electricity consumption) accounts for 82% of the total electricity consumption and other auxiliary electricity consumption totals 18%. The electricity consumption during transitional seasons and summer accounted for 39% of the whole year, and the 5 months in winter accounted for 61%. The total electricity consumption was 45.2 kWh/(m²·a) considering a TFA of 4244.4 m² of this PH building, whereas the average electricity consumption of households (including CD electricity consumption) was 37.2 kWh/(m²·a) considering the same TFA.

Figure 10.

(a) Electricity consumption and distribution of the entire building in 1 year and (b) monthly electricity consumption and distribution. The dark blue is the electricity used by CDs, and the light blue is the electricity used by other things (lighting, sockets, appliances, etc.) in the apartments.

In Figure 10(b), the electricity consumption in 5 months of winter can be broken down, because they are measured separately through two kinds of electricity meters, as listed in Table 5. As shown in Table 10, the average electricity consumption of the CDs in the whole winter is 14 kWh/m², and the average consumption of the household electricity (including the direct electricity in the hot WT – if used) is 9.5 kWh/m² considering a TFA of 4244.4 m² of this PH building.

Table 10.

Components of electricity consumption in the winter.

Electricity	1	2	3	4	5
Electricity	Nov. 2021	Dec. 2021	Jan. 2022	Feb. 2022	Mar. 2022
Total household [kWh]	16,473	22,282	23,762	20,313	17,094
Rest electricity consumption [kWh]	7050	9867	10,305	7776	5240
CD electricity consumption [kWh]	9423	12,415	13,457	12,537	11,854
Averaged rest electricity consumption [kWh/m²]	1.66	2.32	2.43	1.83	1.23
Averaged CD electricity consumption [kWh/m²]	2.22	2.93	3.17	2.95	2.79

As installation of meters on gas lines is prohibited, the natural gas consumption data of the PH building comes from the natural gas company. The annual average natural gas consumption of each apartment in this PH building is 159.9 m³ and equal to 14.6 kWh/(m²·a), which is only used for cooking. In this study, if the energy content of natural gas is simplified to 10 kWh/m³, then the daily average consumption is 4.4 kWh. For comparison, the annual average natural gas consumption of each apartment in the GB building is 175.7 m³ and equal to 20.5 kWh/(m²·a).

The system for preparing DHW is complicated in the PH building, and it is mainly divided into three modes.

Mode 1: The CD and electrical heater can produce DHW at the same time. First, the CD starts to heat the DHW to 45°C and then stops. After that, the electric heater inside the WT starts to heat the DHW to the set temperature of 55–60°C. In this mode, the DHW used subsequently is mainly heated by the electric heater.

Mode 2: Only CD heats the DHW. The CD will heat the DHW to the set temperature of 40–45°C and switch to heat the supply air. In this way, the water temperature in the WT can be a maximum of 45°C.

Mode 3: Only electric heaters heat DHW. They will heat DHW until the set temperature of the WT reaches 55–60°C.

Amongst the 17 apartments that are inhabited, only 6 apartments use mode 2 to produce DHW, which means, the DHW energy consumption of these 6 apartments can be measured due to the heat meters on the pipes of DHW from the CD to the WT (see Figure 5). Hence, these six apartments were selected to analyze the DHW, SHD and household electricity consumption.

As shown in Figure 11 and Table 11, the DHW energy consumption, SHD and household electricity consumption (excluding electricity consumption of CD) of the six apartments in the winter were directly measured and their average value was 46.9 kWh/m².

Figure 11.

Monitored energy distribution of six apartments in the winter: (a) the percentage of the three energy consumption types, arranged in circles from inside to outside are apartments 1 to 6, and (b) the total energy consumption.

Table 11.

Monitored energy consumption in DHW, SHD and household electricity (excluding electricity consumption of CD) of the six apartments in the winter.

Monitored energy [kWh/m²]	Apart. 1	Apart. 2	Apart. 3	Apart. 4	Apart.5	Apart. 6	Average
DHW	3.3	4.4	1.6	2.2	3.8	6.5	3.6
SHD	54.2	20.2	20.4	25.7	44.9	25.7	31.8
Household electricity	21.4	9.3	5.7	10.1	10.3	12	11.5

In addition, based on the DHW, SHD and electricity consumption of CDs monitored in these six apartments, the seasonal performance factor (SPF) at the heating of the CDs was evaluated according to equation (3). SPF is the evaluated performance parameter of the whole heat pump system, and this value can be used as the average efficiency of the heat pump system. As can be seen from Table 12, the SPF of the six CDs during the heating period varied from 2.2 to 3.5. Due to the different usage habits of users, the SPF values are quite different. Moreover, the electricity consumption of CDs also includes the electricity consumption of the fans, water pumps and control systems in the CDs.

{S P F}_{C D} = \frac{Q D H W + Q S H D}{W C D}

(3)

where SPF_CD is the seasonal performance factor [-]; Q_DHW is the heat for the DHW [kWh]; Q_SHD is the heat for space heating [kWh] and W_CD is the electricity for CD [kWh].

Table 12.

SPF of six CDs in the winter.

SPF of CDs	Apartment 1	Apartment 2	Apartment 3	Apartment 4	Apartment 5	Apartment 6
DHW [kWh]	350	472	166	233	408	702
SHD [kWh]	5751	2145	2163	2727	4763	2785
Electricity for CD [kWh]	1744	954	958	1080	2161	1562
SPF [-]	3.5	2.7	2.4	2.7	2.4	2.2

The electricity consumption of 17 apartments was analyzed, and since in one of them, the CD was hardly turned on, this apartment was excluded. As can be seen from Figure 12, there is a huge difference in the proportion of household electricity consumption and CD electricity consumption in 16 apartments. In general, the proportion of CD electricity consumption ranges from 29% to 74% and the average value is 51%, and the remaining 49% is household electricity consumption.

Figure 12.

Ratio of CD and household electricity consumption.

Renewable energy usage

Two kinds of renewable energy sources are used in this PH building. The GSHP is used as a major cooling and heating source. This building is also equipped with a PV system, which consists of 46 polysilicon cells with a maximum capacity of 12.4 kWp. The inclination angle of the south-facing solar panels is 25 degrees (see Figure 2). The electricity production from April 2021 to March 2022 (1 year) was 11,653 kWh, approximately 6% of the total electricity consumption. The energy consumption for DHW in the GB district is 15.2 kWh/m²,²⁵ which is prepared by the solar thermal collectors.

Comparative analysis of simulation tools PHPP and IBE

Besides the PHPP simulation used in the case, IBE software³⁶ was also used to carry out the energy consumption simulation of this PH building. The IBE includes functions such as energy consumption in the design phase, calculation of performance indicators and case evaluation. It can calculate the building’s annual cumulative cooling and heating load, the energy consumption of the HVAC system, DHW system, lighting system and renewable energy system. IBE also considers the requirements of airtightness and a design without TBs. Table 13 gives the results of IBE.

Table 13.

Results of IBE.

Item		Results	Criteria	Are criteria met?
Building energy consumption kWh/(m²·a)		46.5	≤65 kWh/(m²·a)	Yes
Renewable energy kWh/(m²·a) and utilization ratio		17.2	≥10%	Yes
Building performance index	Heating demand kWh/(m²·a)	3.6	≤15	Yes
	Cooling demand kWh/(m²·a)	13.4	≤14.4	Yes
	Airtightness n₅₀	0.5	≤0.6	Yes
Conclusion	The technology of this project meets the requirements of nZEB according to the ‘Technical Standard for nZEB’.⁶

The PHPP, used during design, corresponds to a fully occupied PH building. After this building is put into operation, it is necessary to update the PHPP simulation with the real conditions such as the real occupancy rate and the monitored climatic conditions (e.g. outdoor temperature and global radiation). In summary, the following conditions are updated:

1. The actual occupancy rate (and the corresponding internal heat gains) and the average indoor temperature of this winter are entered into PHPP. It is calculated as one single zone for the entire building and does not distinguish between different apartments.

2. The actual climate data includes outdoor temperatures, global radiation and dew point temperatures.

3. The horizontal shading coefficient was reconsidered, because a new high-rise building, rather than the expected multiple-family house was built on the south side, which had a height of 51.3 m and a horizontal distance of 67 m to the PH building.

Since the monitored data is from 29 apartments and not from 36 apartments, in order to update the PHPP simulation of the whole building, it is necessary to assume the energy consumption of space heating and indoor temperature of the other 7 apartments, as shown in Table 6. For two of the seven apartments that were partly occupied, the average temperature of the adjacent apartments was used, and their energy consumption could be automatically monitored. For five of the seven apartments that were not occupied, the energy consumption was 0, and the indoor temperature was assumed 3 K less than the average temperature of the adjacent apartments. The temperature of the 3 staircases was assumed 3 K lower than the average temperature of the 36 apartments due to no direct space heating. In this way, the SHD of this PH building was calculated to be 21.3 kWh/(m²·a) and the average indoor temperature was calculated to be 21.1°C. Thus, this temperature was then inserted as the indoor temperature in the updated PHPP and this SHD was compared to the SHD calculated by the updated PHPP.

Figure 13 shows the comparison of monitored data and the results of the simulation tools for the SHD. The updated PHPP results in an increase of SHD by 4 kWh/(m²·a). The monitored outdoor temperature and global radiation of this winter impacted the SHD by −3 kWh/(m²·a). The IHG calculated for all apartments was 1.25 W/m² resulting in an additional 4 kWh/(m²·a) of SHD in PHPP. Higher internal temperature and shading from neighbouring buildings increased the SHD by 2 and 1 kWh/(m²·a), respectively. Thus, the updated PHPP calculated an SHD of 12 kWh/(m²·a) which is 9.3 kWh/(m²·a) lower than the monitored SHD for the whole building. The difference between the monitored results and PHPP simulation is mainly because of construction moisture^21,37 and the behaviour of users (an increased use of natural ventilation), which cannot be measured or completely quantified here, since, for example, according to our observations, the doors of unit entrances were often left open rather than closed, although the notice ‘please close the door’ was posted on the doors. In addition, the assumed indoor temperatures of unoccupied apartments and staircases can cause a deviation of SHD. This error consideration is inevitable because of the limitation of monitoring.

Figure 13.

Analysis of calculated SHD in PHPP based on monitoring data and other changes.

The following comparison of the IBE simulation and the PHPP simulation, see Figure 13, is found:

1. From a design point of view, the PHPP certified design (8 kWh/(m²·a)), the IBE result (3.6 kWh/(m²·a)) and the updated PHPP result (12 kWh/(m²·a)) are all less or equal to the criteria of PH 15 kWh/(m²·a). Also, IBE gives a larger deviation from 15 kWh/(m²·a) than PHPP. That means, the SHD of the IBE simulation is too optimistic and IBE has some issues that need to be worked out, for example, the shading effect on the target building by the neighbouring buildings is not considered a boundary condition input in the current version yet. During communication with software developers, they also admitted this was an existing problem.

2. Result of updated PHPP is closer to the monitored energy consumption than IBE.

The data in Figure 13 focuses on the comparison of the SHD because the simulations are all aimed at the energy consumption of space heating, which can be directly compared. The PE simulated by PHPP and IBE was used as an auxiliary reference. The reasons for this consideration are as follows:

1. The scope of PE is different. IBE tool excludes electricity consumption from sockets, cooking and household appliances⁶; however, PH includes all kinds of electricity consumption in the apartment.

2. The coefficients of PE conversion are also different. In China, the standard coal equivalent replaces energy consumption, that is, different types of energy are converted to standard coal equivalent according to low calorific value and coal consumption for the electricity supply of coal-fired generator sets. For PH, the coal consumption of thermal power plants is adopted uniformly.⁶

In addition, a sensitivity analysis was performed in PHPP to identify the range of SHD by varying the IHGs and the indoor temperature (see Figure 14). The SHD varied from 5 kWh/(m²·a) with the highest IHG and the lowest indoor temperature up to 18 kWh/(m²·a) with the lowest IHG and the highest indoor temperature.

Figure 14.

Sensitivity analysis of SHD in PHPP with the indoor temperature and IHG.

Comparison of energy consumption in PH and GB buildings

According to the China Urban Heating Development Report 2021,³² the average SHD in cold regions of China in the winter is about 0.4 GJ/m² (per TFA), which is equivalent to 111 kWh/m². The monitored energy consumption of the GB district in the winter of 2021–2022 showed that with an occupancy rate of 57.8%, the average SHD provided by the district heating company was 155.3 kWh/m². The simulation result of the SHD of the GB district was 134.4 kWh/m².²²

The average electricity consumption of the GB building is 18.6 kWh/m² (from the data of the state grid). Therefore, the site energy consumption of gas, SHD and electricity of the monitored PH building is only 30.8% of the GB building (see Table 14).

Table 14.

Comparison of site energy consumption in PH and GB building.

Energy consumption [kWh/(m²·a)]	PH	GB	Ratio, %
SHD	21.3^a (heat)	155.3 (district heating)	13.7
Gas for cooking	14.6	20.5	71.2
Total electricity (incl. household)	45.2	18.6	243
Sum of site energy (elec. and heat)	59.8	194.4	30.8

^aRemark 2: Not included in the site energy, since the site energy is electricity.

Discussion and recommendations

The energy-saving performance of the PH

From the monitored results, the average indoor air temperature of 29 apartments in the winter is 21.9°C and the corresponding SHD accounts for 28 kWh/(m²·a) on average, which is more than the monitored results in Germany.²² However, this value of SHD cannot be directly compared to the designed SHD 15 kWh/(m²·a) in PHPP mainly for two reasons: a) the occupancy rate of this PH building is 47%, 12 of the 29 apartments were not occupied but heated and therefore, much more heat has been supplied due to a lack of IHG, and b) there were 7 empty apartments (thus, no IHG and the heating system was not in operation) that were ‘heated’ by the neighbouring apartments due to the high thermal fluxes between them (because of temperature difference and very well-insulated thermal envelope). These result in a significantly higher SHD of the investigated 29 apartments than intended during design.

Considering the whole PH building, the SHD was calculated to be 21.3 kWh/(m²•a) and the average indoor temperature was calculated to be 21.1°C, which is higher than the updated value in PHPP by 9.3 kWh/(m²·a). In addition, the monitored data in the first year are often on the high side,^21,38 and some uncertain factors will also bring measurement errors to a certain extent such as construction moisture and users’ behaviour. Various lifestyle habits of families and their usage patterns of CD lead to different energy consumption in these apartments. One more reason could be that the inhabitants probably opened the windows more often than in other years due to the pandemic. If the occupancy rate could reach 100%, the SHD could be expected to be close to the target of 15 kWh/(m²·a). Although there is a difference between the monitored and designed SHD, the SHD of the PH building is only 13.7% of the SHD of the GB building, saving 86.3% energy consumption. This result is consistent with a previous article, in which the PH building was found to consume only 11% of space heating required by the GB building.²⁵

The PE consumption converted from household electricity and total electricity consumption was 96.7 kWh/(m²·a) and 117.5 kWh/(m²·a), respectively, both of which are less than the limit of 120 kWh/(m²·a) required by the PH standard if the PE coefficient is assumed to be 2.6.¹¹

In the summer, the electricity consumption was relatively lower. According to the questionnaire of some inhabitants, many of them did not turn on the CDs for cooling in the summer due to habitual ‘cost-saving behaviour’ and relied entirely on natural ventilation or electric fans to cool down. This is one of the main reasons why the electricity consumption in the summer does not have the same ‘peak’ as in the winter (see Figure 10). In addition, the occupancy rate last summer was not as high as in the winter, many residents moved in before winter. So, the total electricity consumption for cooling was not as high as during the heating period.

In the PH building, the total gas and electricity consumption was 59.8 kWh/(m²·a) and the proportion of electricity consumption was 75.6%. On 11^th March 2022, the MoHURD officially released the ‘14^th Five-Year Plan for Building Energy Efficiency and Green Building Development’, proposing that the proportion of electricity consumption in urban building energy consumption should exceed 55% by 2025. So, this PH building has reached this regulation.

Figure 11 and Table 11 show the range of different energy usages of the apartments in the winter. The SHD was the largest part of energy consumption, followed by household electricity consumption and DHW energy consumption was the least. The energy consumption for DHW is less, partly because electric kettles are used to boil water for tea, coffee and cooking, and there is no hot drinking water from the WT directly. Part of the energy consumption of DHW is transferred to the household electricity consumption, because of the use of an electric heater in WT.

Figure 12 indicates that in the winter months, the average CD electricity consumption is almost equal to the household electricity consumption considering all the inhabited apartments in the PH building.

The equipment and methods required to achieve high energy-saving in PHs requires a large initial investment and good operational management in comparison with the conventional GB buildings. Their economics were analyzed in detail in previous publications.²⁵ The result is that the initial investment of PHs exceeds that of GB building by ¥864RMB/m², which can be recovered in 17 years through energy-saving during the operational period.

Better indoor environment in the PH

The goal of reducing building energy consumption has to be done without lowering the comfort of the indoor environment. The indoor temperature was set at 20∼26°C and the set points of relative humidity are 30%–60% throughout the year in this PH building. Figures 15 and 16 show the monitored indoor temperature and relative humidity of PH buildings in the winter.

Figure 15.

Monitored average indoor temperature.

Figure 16.

The CDF of the monitored indoor relative humidity in November 2021 in 17 inhabited apartments.

The monitored IEQ of this PH building shows that the average internal air temperature and relative humidity have reached the comfort zone³⁹ stipulated by the PH standard. Users’ complaints about uncomfortable conditions have been significantly decreased compared with the previous winter. Due to differences in users’ habits, the average monitored air temperatures of 29 apartments fluctuated from 16.6°C to 23.6°C, with an average temperature of 21.9°C compared to the average outdoor temperature of 4.5°C. One of the apartments was not often occupied, resulting in the lowest average indoor temperature of 16.6°C. The overall relative humidity in the building was also very suitable, distributed in the range of 29%–48.9%, and the average relative humidity was 37.2%. The duration of the relative humidity falling below the lower limit of 30% was significantly reduced (e.g. Figure 16), which shows that it is more comfortable than the adjacent PH public building PHTEC.¹¹ Indoor CO₂ concentrations also remained very low, within 800 ppm, highlighting the advantages of a mechanical ventilation system that continuously provides fresh air. The interior environment of this PH building generally maintains a high degree of comfort.

Recommendations and limitations

Besides the building envelope and service systems, users’ behaviour is also important when discussing PH building energy performance.

The PHI does not recommend an insulation layer on the house partition walls to reduce the heat³⁸ and noise transfer; however, footstep sound insulation is recommended in the intermediate ceilings and has been proven to be sufficient. This PH building was built as the PHI recommended. During the operation, many inhabitants complained about noise being heard through the partition walls. Hence, it is recommended that a sound and heat insulation layer can be added to the partition walls of the PH residential buildings in the future, to meet the requirements of Chinese residents. For example, on both sides of the partition wall, 40 mm thick rock wool could be added for a thermal and sound insulation layer. In this way, within the building envelope, the already occupied apartments do not need to consume additional energy to heat the vacant apartments, and more importantly the noise transmitted through the partition walls would be reduced.

During a survey of some residents, insightful operating experiences were shared. 1) Maintain the room temperature at 25°C in summer and 21–22°C in winter. Try not to open windows in winter and summer. 2) Adjust the set temperature according to weather changes throughout the year. 3) Open windows for natural ventilation and turn the CD off during transitional seasons. 4) In winter, increase the set temperature and do laundry during the discounted electricity hours (between 8 p.m. and 8 a.m.) to save electricity costs. 5) The design of the HVAC system should be as simple and intuitive as possible, allowing users to reduce manual operation and mode conversion, otherwise, misoperation could occur, resulting in operating problems and an increase in energy consumption. Such operating strategies are publicly recommended to more residents to improve the operating efficiency of their apartments and achieve the purpose of energy-saving and reduction of CO₂ emissions. Hence, user’s manuals are delivered to improve energy-saving behaviours.

Highly efficient thermal insulation, passive doors and windows, high level of airtightness, TB-free design and construction together with CD ensure that this project results in high energy efficiency and high IEQ. In addition, the commissioning of the CD that was carried out in the winter of 2020 provided the necessary guarantee for smooth operation this winter. Therefore, PHPP simulations and construction quality control are important methods to realize successful PHs.

As mentioned above, passive technology and active performance optimization provide an explicit path to promote energy-efficient buildings – PHs, which can be applied not only in cold climate zones but also all kinds of climate zones. If the minimal amount of energy consumed by PHs can be covered by renewable energy, then the building can reach a level of net-zero energy consumption.

The research results of this article are only based on the monitoring of the first heated winter. The project should be continuously monitored for 2–3 years including cooling energy consumption, and more feedback from residents on usage habits can be obtained through questionnaires.

Conclusions

The PH residential building is monitored concerning the energy performance. The main conclusions are as follows:

1. This PH building operates properly in the cold climatic region and shows great energy-saving potential; meanwhile, it also provides a comfortable indoor environment. The SHD is only 13.7% of local conventional GB buildings, resulting in an 86.3% energy-savings. The total site energy consumption for the whole building is only 30.8% of the GB building. So, PH technologies can be widely promoted in cold climate zone in China.

2. When the occupancy rate of this PH building is 47%, the SHD is 28 kWh/(m²·a). The SHD generated in initial PHPP design was 8 kWh/(m²·a), the SHD of updated PHPP was 12 kWh/(m²·a) and the monitored SHD was 21.3 kWh/(m²·a). The monitored SHD was 9.3 kWh/(m²·a) higher than the simulated in updated PHPP. The main reasons for the difference in SHD are construction moisture, users’ behaviour and occupancy rate.

3. By comparing the simulation results of PHPP and IBE, a deviation was found. This project provides evidence that an update of IBE is desirable. Hence, PHPP is always recommended for the design of PHs. The study also indicates that the performance-oriented design, refined construction and robust system commissioning are prerequisites and favourable guarantees for realizing reliable PHs.

This case study provides a path to the actualization of the ‘Carbon emissions peak before 2030 and carbon neutrality before 2060’ targets. If more PHs could be built and monitored in different climatic zones in China in the future, the accumulated data would help to optimize the design and construction of PHs in different regions, resulting in improved savings and energy efficiency.

Footnotes

Acknowledgements

We thank all of colleagues from the Sino-German United Group in Qingdao for opening the PH building district and its drawings for us. We also thank the colleagues from PHI for their support in the PHPP simulation. We would also like to thank all of the residents of this PH building for their friendly cooperation during the monitoring period.

Authors' contributions

Fei Han undertook the main review tasks, writing and analysis of the monitoring. The monitoring and the commissioning of the HVAC were carried out by Bin Liu. Georgios Dermentzis approved the monitoring process and results. Wolfgang Feist and Rainer Pfluger contributed to the conception and reviewed the results.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Fei Han

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