Effects of different heating modes on room temperature and heat consumption of existing residential buildings in rural areas

Affected by economic conditions, living habits and other factors, residents in rural areas have a high sense of self-regulation when heating. Rural residents often choose the corresponding heating mode according to the specific situation. This paper takes an existing building in the countryside of Zhangjiakou as the research object. The room temperature change and heat consumption under different heating modes are simulated and analyzed. The results show that the temperature of each room is higher than that of the natural room temperature under different heating modes. Even if the room is not heated during the day, the room temperature can be maintained at more than 10 °C. When the heating temperature is set to 18°C in the active state and 14°C in the sleeping state, the heat consumption can be reduced by up to 32.05% in each heating mode. The heat consumption of each mode is comparatively low, and the room temperature in each time period is similarly lower, when the heating temperature of all states is set to 14 °C.


Introduction
Different from urban central heating in winter, in rural areas of China, most of the early heating methods were household coal-fired furnaces, electric furnaces and biomass furnaces, using energy such as coal, biomass and electricity [1] .With the promotion of heating transformation work such as "coal to gas" and "coal to electricity" [2] and the implementation of the "double carbon" policy [3] in China, the heating methods in rural areas have changed from coal [4,5] and fuel, which are more polluting and less efficient, to the more clean and efficient gas wall mounted furnaces, air source heat pumps, ground source heat pumps and other heating methods [6,7] .Even so, compared with the indoor thermal environment created by centralized heating in cities, there is still a gap in indoor thermal environment in rural areas during winter heating [8] .Rural dwellers have a higher level of self-regulation when it comes to heating in the winter, which is influenced by the local economic status and individual living habits [9] .Thus the indoor heating temperature regulation is relatively low.
Varying families have varying needs for heating temperatures in rural dwellings since each room serves a distinct purpose.Some farmers often decide whether the room needs heating and the time and temperature of heating according to their perception of the ambient temperature and the time spent in the room.Furthermore, due to production methods and other factors, people in rural areas must enter and exit the room frequently, and farmers' clothing should be based on the fact that they will not feel cold during short-term outdoor activities, determining that the heating temperature of rural houses in winter is generally lower than that of urban houses (18℃) [10] .According to the survey and test results, the temperature range of most rural households' bedrooms and living rooms in winter is 5-13 ℃, and .Therefore, the different requirements of rural residents for the indoor thermal environment determine the different heating modes in winter.However, residents lack an intuitive understanding of the specific changes in indoor temperature and heat consumption caused by different heating modes.
This paper takes an existing house in the rural area of Zhangjiakou, China as the research object.Based on the influence of residents' heating behavior on indoor thermal environment, the changes of functional room temperature and heat consumption under different heating modes were analyzed.Under the guarantee of a suitable indoor heating temperature range, heating energy consumption is minimized to the greatest extent feasible, providing a reference for farmers to pick a reasonable heating strategy.

Model Building
The subject of this research is a traditional building constructed in 2010 in Zhangjiakou City, Hebei Province.It has two storeys and a total building area of 280 m 2 , with dimensions of 20 m, 7 m, and 3.6 m, as indicated in Figure .1.The walls are made of solid clay bricks.The external wall of the building shall be insulated.The thermal insulation material is extruded polystyrene board, and its thermal conductivity is 0.036 W /(m•k), and heat storage coefficient is 0.353 W/(m 2 •k) [14] .The roof is a pitched roof with a slope of 30° and a height of 1.5m formed of wood purlins, wood planks, and clay tiles.All rooms have Windows on the south wall with 2×2 m ordinary hollow glass Windows.Ordinary insulating glass is installed in the corridor to form a sunlight room and improve the passive solar energy utilization rate.The main door size of the living room is 2×2 m, and the rest are 1×2 m wooden doors.As shown in Table 1.

Simulation conditions
This research is being conducted in Zhangbei County, Zhangjiakou City, Hebei Province, which is located in a severe cold environment [15] .The coldest month of the year, as indicated in Figure .2, is January, with an average temperature of less than -5℃.January 1 is the coldest day, with an average daily temperature of -18.73℃, the highest daily temperature of -9.1℃, and the lowest temperature of -25.5℃.

Natural room temperature
To study the change of indoor temperature and heat consumption before and after heating under the most unfavorable meteorological conditions.Now the rooms are set as 1A, 1B, 1C, 1D from west to east (2A, 2B, 2C, 2D on the second floor), as shown in Figure 1.January 1, with the lowest outdoor temperature, was chosen as the typical day and January as the typical month.The DeST-h software was used to simulate the hourly changes of room temperature under natural conditions before and after the building refurbishment on January 1 (00:00 to 24:00), as shown in Figure 3.As can be seen from Figure 3, on the coldest day (January 1), the daily temperature of rooms 1A, 2A, 1D, and 2D varies substantially, and room 2A remains the coldest, at a temperature of -0.47℃.Rooms 1B, 1C, 2B, and 2C may attain temperatures of more than 4℃, and when compared to other rooms, the temperature is high and the variation is moderate, making them ideal for the master bedroom and living room.Because the outside protective structure of 1D and 2D rooms is smaller than that of 1A and 2A rooms, the temperature is relatively high, and they are better suited for common secondary bedrooms.Therefore, 1B and 2B can be set as the master bedroom, 1C and 2C as the living room, and 1D and 2D as the second bedroom.

Simulation Scheme
Because the thermal environment requirements of each room in a rural home change, the heating temperature necessary for different periods of time may also differ.In order to study the temperature change and heat consumption of the heating room under different heating modes when heating rooms B, C, and D, four common heating modes are now divided into [16][17][18] .The heating temperature is classified into two categories.In the first scenario, different heating temperatures are set based on personnel states.The heating temperature is 18 ℃ when active and 13 ℃ when sleeping [18] .However, even in the active condition, the indoor temperature setting of rural residents in winter heating is frequently lower than 18 ℃, and the indoor heating temperature remains constant regardless of state; thus, the second case is set at a 14 ℃ heating temperature, as indicated in Table 2.

Simulation and analysis
4.1.The room temperature and heat consumption simulation were examined in the case of the first heating temperature.

Room temperature simulation and analysis.
According to the above scheme, using DeST-h software to simulate the building, it is possible to obtain that during the coldest day (January 1), different heating modes are used, and the temperature of the heating room changes from time to time, as shown in Figure 4. higher than it would be under natural conditions, whether the room is heated or not.In mode 1, during the day, the temperature in each room is kept at the active state's interior design temperature (18 ℃).Except for the two rooms 1D and 2D, the temperature decreased to the interior design temperature during the evening sleep state, requiring a brief heating.The other rooms' temperatures did not go below 14 ℃, and no heating was required.In mode 2, because rooms B and D are used as bedrooms and are only heated at night, the maximum room temperature is 13 ° C.After the heating was turned off during the day, the temperatures in rooms 1D, 2B, and 2D all dropped, with the lowest dropping to around 10 ℃.Room 1B is consistently at 12 ℃ and does not require heating.During the heating time, the room temperature in Living Room C is maintained at the predetermined temperature, and once the heating is turned off, the room temperature is decreased to a minimum of 14 ℃.In mode 3, the second bedroom 2D needs to be heated throughout the night, while the second bedroom 1D begins heating when the room temperature falls to the lower limit of tolerance (11 ℃) at 0 o'clock and the room temperature during the day is between 10 and 13 ℃.Although master bedroom B's heating time is set for all-day heating, the room temperature does not dip to the specified heating temperature during sleep, so there is no need for heating.The temperature change in living room C is comparable to mode 2. In mode 4, the room temperature of master bedroom B is higher than 13℃ while sleeping, so no heating is required.Around 01:00, the temperature in the second bedroom D falls below 13 ℃, necessitating the use of heat in the room.Rooms B, C, and D need to provide heat to the room in the active state in order to keep the room temperature at the stated setting.As a result, in the active state, each functional room needs to be heated in order to keep the room temperature at the interior design temperature.Except for heating mode 2, the other modes may keep the master bedroom and living room temperatures above 13 ℃ all day.The master and second bedrooms in mode 2 and the second bedrooms in mode 3 are only heated at night during sleep; thus, the room temperature can only be maintained at 10-13 ℃ during the active state, and the body feels bad.

Energy consumption simulation and analysis
As illustrated in Figure 5, DeST-h was used to simulate the heat consumption of each room throughout the course of the winter using various heating settings.The heat consumption in January was statistically evaluated, and it was discovered that, among modes 1 to 4, mode 1 was continually heated throughout the day, resulting in the largest total heat consumption, up to 3060.39 kW•h.Because mode 2 has the shortest heating time, it has the shortest heat consumption, at 2079.43 kW•h, which is 32.05% less than mode 1. Modes 3 and 4 consume nearly the same amount of heat, 10.3% and 11% less than mode 1.When the heating duration and level are the same, the heat consumption of the second bedroom in modes 1, 2, and 4 is 29.88%, 64.73%, and 23.53% more than that of the master bedroom, respectively, according to Table 2.In mode 1, the heat consumption of the second bedroom is 13.7% higher than that of the living room.In mode 4, the heating time for the living room is shorter than for the primary and secondary bedrooms, resulting in decreased heat use.However, in modes 1-3, the heat consumption of the living room is higher than that of the master bedroom: 18.74%, 77.98%, and 29.18%, respectively.As shown in Figure 6 (d), when the heating temperature is set to 14 ℃, the heat consumption of different heating modes varies little, with mode 4 having the lowest heat consumption being only 10.16% less than mode 1 having the highest heat consumption.The heat consumption of the second bedroom is pretty considerable in each mode, regardless of the exterior climate, whereas the heat consumption of the master bedroom is relatively little.When the heating in the room is turned off, the change trend of the room temperature in modes 2 to 4 is comparable, and the room temperature drops by the same margin, and they are all within 10 to 14℃.

Solution discussion
In the first heating temperature setting, mode 1 consumes the most heat.However, the room can be kept at a set temperature at all times, which is suitable for situations with high indoor thermal environment requirements.Mode 2 consumes the least heat, which is 32.05% less than mode 1.Each room is functionally distinct, and the primary and secondary bedrooms are in the active state at a lower room temperature.Therefore, it is only suitable for use when resting at night and is not suitable for use as a daytime activity place.Although the living room is only heated during the day, the room temperature can still be maintained at more than 14 ℃ at night.As a result, mode 2 is more suited to situations in which residents' activities are centered in the living room during the day and the living room temperature is not very low at night.The heat consumption of the master bedroom is nearly the same in modes 3 and 4, and the temperature of the master bedroom and living room may be kept in a more comfortable range (13-16 ℃) throughout the day.It is better suited to situations in which the master bedroom and living room are the primary living spaces.
The heat consumption of each mode is the same in the case of the second heating temperature setting.Except for the fact that the temperature in each functional room in mode 1 is kept constant at around 14 ℃ throughout the day, the temperature in the other mode rooms varies between 10 and 14 ℃.The temperature in some rooms is low, especially between 08:00 and 22:00, and the bodily sensation may be unsatisfactory if used as an activity location.As a result, when comparing the room temperature and total heat consumption at each time under the heating temperature of case 2, mode 1 is superior.

Conclusions
Using an existing building in a rural location of Zhangjiakou as the research object, this work created a model with DeST-h software and simulated the temperature change and heat consumption of each functional room in the coldest month (coldest day) using several heating modes.Following a comparative analysis, the following results were reached: (1).During any time of the heating season, the room temperature in various modes increased to varying degrees as compared to the natural room temperature.During the day, even after some rooms (such as the living room in modes 2 to 4) stop heating, the room temperature can be kept between 13 and 16 ° C, which is more comfortable.
(2).When the heating temperature is 18 ℃ in the active state and 14 ℃ in the sleeping state, mode 1 has the highest heat consumption (3060.39kW•h) and mode 2 has the lowest (2079.43kW•h), which is reduced by 32.05%.Furthermore, as long as the room is heated in the active mode, the temperature can be kept above 13 ℃ throughout the day.A room heated exclusively during sleep can sustain a temperature of more than 10 ℃.
(3).In all states, the heating temperature is 14 ℃.The room temperature can be kept at 14 ℃ by heating it.When the heating is turned off, the temperature change trend in each room in each mode is similar, and the room temperature declines by the same margin.The indoor temperature can be kept within 10-14 ℃.Mode 1 has the largest heat consumption at 2332.76 kW•h.Mode 4 has the lowest heat consumption at 2095.8 kW/h, a drop of around 10.16%.Furthermore, when comparing the lowest energy consumption mode 2 in the first room temperature setting to the highest energy consumption mode 1 in the second room temperature setting, the heat consumption only increased by 253.33 kW•h, or approximately 10.86%.

Figure 2 .
Figure 2. Annual outdoor dry bulb temperature in Beixian County.

Figure 3 .
Figure 3. Hourly variation of room temperature in buildings on the coldest day.

Figure 4 .
Figure 4. Temperature change of each functional room in heating mode 1 to 4.
2023 5th International Conference on Energy, Power and Grid (ICEPG 2023) Journal of Physics: Conference Series 2703 (2024) 012005 4.2.The room temperature and heat consumption simulation were examined in the case of the second heating temperature.The temperature change of the heating room in different heating modes during the coldest day (January 1) can be obtained in the second scenario if the heating temperature is set at 14 ℃, as shown in Figure.6.(a) Mode 2 (b) Mode 3 (c) Mode 4 (d) Heat consumption Notice: In mode 1, each room temperature is maintained at 14 ℃ throughout the day.

Figure 6 .
Figure 6.Room temperature and heat consumption at 14℃ heating temperature.

Table 1 .
Material selection of envelope structure.

Table 2 .
Heating mode of each functional room.