District heating (DH) in northern China is a crucial component of building operations, energy consumption, and carbon emissions. It is also an important livelihood project to ensure a comfortable life for residents in winter. Due to the vast territory, the area of buildings with heating systems in northern China reached 15.6 billion m
2 in 2020, and the total energy consumption reached 214 Mt of standard coal equivalents (tce, 1 tce = 29.307 GJ), with a total carbon emission of 450 Mt CO
2 [
1]. In the macro-energy strategic goal of “carbon peak and carbon neutrality,” the carbon-reduction task for building operations is arduous, and the same is true for residential DH systems [
2].
The energy use intensity (EUI) of DH in northern China has dramatically reduced over the past two decades. Control measures for the energy consumption and carbon emissions of DH have developed with technological advancements, including the use of efficient and clean heat sources, such as the utilization of thermal-power-plant waste heat [
3], industrial waste heat [
4], low-loss distribution pipeline networks, and building envelope improvement [
5]. The reform of heating marketization has not achieved apparent consequences in the mechanism aspect. Implementing “heating metering” for users and charging according to the metered heat is key to the reform [
6,
7,
8]. The main promotion method is installing a household heat meter, referring to experience from Northern Europe [
9].
Despite the fact that approximately a 2 billion m
2 heating area in northern China had meters installed through financial investment, barely any households are charged with metered data [
10]. The reasons are summarized as follows: heat transfer between households [
11,
12], stoppage by heat users [
13], and meter quality [
14]. This results in household meters malfunctioning. Thus, to understand the dilemma of heat reform and household heat metering in northern China, it is necessary to study the thermal characteristics of meter users and their regulation behavior.
1.1. Study of Heat Metering
The aim of promoting heat metering is to (1) promote the implementation of buildings’ energy-saving standards and reduce heat energy consumption; (2) promote energy-saving behavior among users and reduce excessive heating caused by overheating or heating vacant rooms; and (3) improve the quality of heating services and achieve on-demand heating [
15]. However, metering only involves data detection and cannot lead to energy savings directly.
As household metering is the leading heat metering technology promoted in northern China, many studies have focused on the heat transfer between households through experiments, simulations, and onsite surveys as a basis for correcting user heat fees. Zhan et al. [
16] found that heat transfer between households accounts for 9.3–47.2% of the total heat consumption of typical users through onsite measurements. Ling et al. [
17] proposed various location correction factors in seven cities that regulate metered heat data to achieve a fair distribution of heating costs among households. Liu et al. [
18] analyzed the factors of heat cost allocation through simulation. They proposed that users in the building allocate the heating cost according to the accumulated time of valve opening. The data from household meters cannot be used directly [
19], which significantly increases the cost of equipment and calculations, resulting in a lack of enthusiasm for heating companies and a low degree of user recognition.
Therefore, it is necessary to reexamine the heat metering technique, which is regarded as an energy-saving technology for buildings. In particular, the energy saved must be evaluated at the system level. For a DH system, energy saving is achieved only when the total energy consumption of the heat source (such as a boiler or a thermal power plant) decreases for the same area [
20]. The heating station is the smallest unit in the secondary system, i.e., the energy-saving effect of heat metering should be fed back to the heating station. Meanwhile, the heating EUI is a key evaluation indicator for every DH system level.
1.2. Influence of User Regulation on Heat Energy Consumption
Owing to the continuous operation of heating systems, the energy-saving potential of regulating user behavior has always been a controversial topic. Canale et al. [
21] conducted a comprehensive review of the technical means, energy-saving effects, charging methods, and cost effectiveness of heat metering in EU countries. It was pointed out that the energy-saving effect of metering is due to the combined influence of the temperature control valve, user behavior, and charging mechanism rather than the installation of heat meters [
22]. For studying the actual energy savings of household meters, 105 household heat metering users were selected, and it was found that users can reduce their heat by 5% by reading the meter and can save 3% to 9% of their heat using other feedback methods [
23]. Lynham et al. [
24] found that energy consumption can be reduced by displaying real-time energy consumption information to residents. In addition, it is more cost effective to help residents understand the energy consumption of their daily behaviors through education and signs.
However, the policy attitudes of some EU countries have changed in recent years. The Swedish National Housing Administration recommends that households should meter no new buildings for heating or domestic hot water [
25,
26]. The Danish Energy Agency defines cost effectiveness as the life-cycle energy saving of heat meters being greater than their purchase and installation costs but found this largely impossible to inspect [
25]. For the heat metering of existing apartment buildings in Finland, it was not possible to achieve cost effectiveness through behavioral energy savings, and investments to control and balance the heating network were proposed to be more effective than indirect measures [
27].
Smart meters and algorithm control could be effective in small-scale DH systems [
28,
29,
30]. An algorithm, coupling downsized heat pumps to radiant emitters, based on thermal inertia control was studied and the seasonal performance of heat pumps increased by 10% [
31]. Although there are control systems, the behavior of users opening windows is also worth considering. Even for retrofitted buildings, ventilation loss may still account for 70% of total heat loss [
32]. In addition, users often worry about differences in heating costs, so a method that calculates minimum and maximum heating costs was studied to help allocate heating costs in multifamily buildings [
33].
Typical residential buildings in the severely cold regions of northern China are large apartment buildings, whose number of households is much higher than that in European countries. Therefore, the characteristics and behavior of users in multifamily buildings in northern China need further study.
This study is focused on investigating the thermal characteristics of typical buildings in DH systems in northern China.
Section 2 explains the analysis methods and research objectives of this study. The field tests and data collection were conducted at the scales of heating stations, buildings, and households in several heat metering pilot cities.
Section 3 proposes the definition of the regulation behavior index of users to quantify regulation characteristics. Combined with the user behavior on installed heat meters, the actual regulation needs and regulation characteristics of users were analyzed from a microscopic perspective. In
Section 4, the main influencing factors of the heat energy consumption of DH systems are summarized, and three factors, namely, household location, heat outages, and user adjustment, are analyzed in detail.
Section 5 summarizes the significance of heat metering and the necessity of regulation based on the results. Finally,
Section 6 discusses technical route ideas suitable for apartment buildings in northern China.