| There is a huge potential of building energy efficiency in rural areas that people pay more and more attention to.The problem of the supply of heat in the rural areas is always a focus of people’s concerning.Since a long time,there are many disadvantages in the conventional heating system of a coal fired boiler and radiators,such as the poor burning effect of coal which results in the tremendous soot,which pollute the environment.In addition,coal pollution has also had a huge impact on the formation of fog and haze.In order to reduce the coal dust pollution in Beijing in winter,especially in rural areas,and improve air quality in Beijing,Tianjin and Hebei,many cities in northern China come up with police of coal to electricity,reducing coal and replacing coal and other related policies.As an introductory line of heating equipment in work of coal to electricity in northern rural areas,air source heat pump attracts people’s attention,but the temperature of hot water generated by air-source heat pump is usually lower than 55℃,but the original heating system with radiators was widely used by rural buildings.If the electric air source heat pump can be used to replace coal-fired boiler directly,and the form of indoor heating system does not need to be changed but only be added a certain number of radiators.This way of transformation is more accepted by users.Therefore,it is necessary to study if the low temperature hot water with radiators can meet the needs of indoor heating load and the thermal comfort of users in this room.Test the air temperature in rooms,the temperature of supply and return water in system,the heat supplied for the building and the power consumption of the system.The results show that this kind of low temperature radiator heating system can meet the indoor thermal comfort.During the test,the heat load index of this rural house is 43W/m2,and the indoor air temperature is 17℃.In addition,the COP of the system is about 2.8 and the temperature difference between supply and return water is 1.6℃.This system adopts the method of calculation in simulation design that is increasing 1 time the number of the radiator slices,and the system runs well during the test period.It is confirmed that the system can certify the indoor air temperature that is needed for normal life,and the COP of the system is over 2.5 under low outdoor temperature,so this low temperature water heating system can be applied in rural areas in Beijing.An economic analysis model of air source heat pump and radiator heating system is established,the economic calculation and analysis of the system is carried out by using the annual cost method,at the same time,the economy and energy efficiency of the loose coal stove,coal stove and gas boiler heating systems were compared and analyzed.The result shows that the initial investment of air source heat pump and radiator heating system is higher,which is about 8.2 yuan/m2,while its operation cost is lowest,which is about 23.8 yuan/ m2.From the annual cost,the annual cost of air heat pump heating system is lowest,which is 32.0yuan/ m2.From the view of energy saving,the systems with air-source heat pump and gas boiler as heating sources have a good effect,and the emissions of the traditional small coal-fired boiler is serious,and the heating efficiency is low,which means it has the problem of serious waste of energy.Using CFD commercial software—Airpak to establish the physical and mathematical model of a building before and after the transformation,and the indoor temperature field and PMV distribution of the high temperature water and low temperature water heating systems are simulated under the outdoor temperature of-7.6℃ and 0.88℃,individually.By numerical simulation,the conclusion is that after doubling the number of the radiators,the systems with high temperature(the average temperature of radiators’ surface is from 55℃ to 70℃)and low temperature water(the average temperature of radiators’ surface is from 35℃ to 43℃)have the similar indoor temperature distribution and thermal comfort.When the surface temperature of radiators is 43℃,the average temperature of the level of people sitting height(the height is 1.2m)is 15.4℃,in addition,the average PMV is-0.379 under the condition of outdoor design temperature in heating.While the surface temperature of radiators is 38℃,the average temperature of the level of people sitting height(the height is 1.2m)is 17.8℃,and the average PMV is-0.028,under the condition of outdoor actual average temperature in test.So,the low temperature water radiator heating system can be used to meet the requirements of indoor thermal comfort in rural buildings in Beijing.Simulate a typical rural house load change with continuous and intermittent heating modes by EnergyPlus that is a software for energy consumption simulation,and analyze the characteristics of the intermittent heating load in the condition of meeting the requirements of building thermal energy saving design.Comparing with continuous heating system,the energy saving rates of stopping heating 3h,6h and 9h were respectively 3.01%,6.11% and 10.35%,while the corresponding additional rate of equipment capacity were 5.07%,24.8% and 40.7%.In the early and late cold periods,the indoor temperature drop is smaller,during stopping heating 3~6h,indoor temperature drop is lower than 3℃.In the freeze-up period,the indoor temperature drop is lager,so it is not suitable to adopt the intermittent heating mode during this period.In addition,the data shows that the insulation pattern of building envelopes has little influence on energy consumption while using intermittent heating mode.But when the external wall adds 50 mm polystyrene board as external insulation measures,the energy consumption can be reduced about 60%,compared with the exterior wall without any insulation measures.Therefore,the work of coal to electricity in rural areas should be based on the energy saving transformation of the original rural residential building envelope,to improve the thermal storage and thermal insulation performance of the building envelope structure. |
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