Research On The Design Theory And Application Of Low Temperature Heating Systems Combined With Dedicated Outdoor Air Supply Systems Based On Productivity

Nowadays, the problems with regard to energy, health and environment aregrowing rapidly in the world. The design goal of HVAC system is to make peoplework efficiently and productively in comfortable, healthy, and energy efficientenvironments. The low temperature heating systems (LTHS) combined withdedicated outdoor air supply systems (DOAS), which can create a healthy,comfortable, energy efficient and productive indoor thermal environment, hasgreat potential and application value to be the future of the HVAC systems. Thisstudy focus on the design theory and application of LTHS combined with DOASbased on productivity, involving relation between indoor thermal environment andproductivity and building heat load when an office room with LTHS and DOASwas regard as the research object.Human exergy balance model was established according to the second law ofthermodynamics and based on Gagge‘s human balance model. Human body exergyconsumption formula was derived based on the human body exergy balancemodel. Effect of indoor operative temperature and human thermal sensation on thehuman body exergy consumption and productivity in typical office building werestudied by analyzing the data obtained in simulated office environments in winterusing the human body exergy consumption formula. The results show that humanbody exergy consumption and productivity are inversely as operative temperaturechanges from17to28℃or human thermal sensation changes from-1.0to+1.4,and that human body exergy consumption reach its minimum and productivityreach its maximum when indoor operative temperature equals19℃or thermalsensation equals-0.56, and the change of human body exergy consumption resultsin the change of productivity in slight cool and slight warm indoor thermalenvironment.Experimental studies of indoor thermal environment and ventilationeffectiveness in a room with low temperature radiant floor heating systemcombined with mixing ventilation system and displacement ventilation system asradiant floor surface temperature ranges from25to29℃, supply air temperatureranges from15to19℃and supply air flow rate equals224l/s. The results showthat the distribution of indoor thermal environmental parameters are relativelyuniform, the indoor vertical air temperature differences are less than1℃andventilation effectiveness is approximately1.0when low temperature radiant floorheating system is integrated with mixing ventilation system. The distribution ofindoor thermal environmental parameters are relatively non-uniform, the indoor vertical air temperature differences are large and up to4℃and ventilationeffectiveness is approximately1.1when low temperature radiant floor heatingsystem is integrated with displacement ventilation system.Indoor temperature prediction models in a room with LTHS combined withmixing ventilation system or displacement ventilation system were establishedbased on the characteristics of indoor air flow. Compared with the experimentalresults, the data predicted by these models agree well with the experimental data.The difference between indoor design temperature for calculating building heatload and indoor operative temperature for evaluating the indoor thermalenvironment is pointed out according to the formula. Correcting on the indoordesign temperature based on the indoor operative temperature for maximumproductivity were performed The results show that correction of indoor designtemperature is0.4~1.0℃in a room with LTHS combined with mixing ventilationsystem and0.6~1.2℃in a room with LTHS combined with displacementventilation system when external envelope heat loss ranges from20to50W/m2.Heat transfer model of low temperature forced convector with multi-pass fintube heat exchanger as core compartment was established. The numbers of heattransfer unit (NTU) formulas of multi-pass fin tube heat exchanger were derivedbased on the heat transfer model. Subsequently, a two-pass fin tube heat exchangerwas selected as test case to validate these NTU formulas. The results show that theheat transfer coefficients of the heat exchanger calculated by these NTU formulas(ε-NTU method) agree very well with that calculated by logarithm meantemperature difference formulas (LMTD method), under the condition of inletwater temperature from45to60°C and water flow rate from50to170kg/h.Factor analysis of effect on the heat transfer coefficients of fin tube heatexchanger were performed using these NTU formulas. The result shows that theheat transfer coefficients of fin tube heat exchanger are related to the water flowrate but not the mean temperature difference.The equivalent thermal resistance model for calculating heat dissipation oflow temperature radiant floor based on shape factor was established. The resultscalculated by the equivalent thermal resistance model based on shape factor werecompared with numerical simulation. The results show that the relative errorsbetween heat dissipation calculated by the equivalent thermal resistance modelbased on shape factor and calculated by the simulation software are less than5%as the tube space ranges from50to300mm, the distance above pipe ranges from25to65mm and average hot water temperature ranges from25to45℃. Then theequivalent thermal resistance model based on shape factor was used to analyze theimpact of factors on the heat dissipation of low temperature radiant floor. The results shows that the distance above pipe has no significant effect on the heatdissipation of low temperature radiant floor, and the average water temperatureand tube space have a big effect on the heat dissipation of low temperature radiantfloor.The supply water temperature adjustment relationship of low temperatureforced convector heating system and low temperature radiant floor were derived.Low temperature forced convector heating system and low temperature radiantfloor heating system in a mixing ventilation room in a typical office building wereselected as research objective, and effect of indoor temperature set-up values onthe indoor human thermal sensation distribution, productivity distribution andsystem energy consumption were studied. The results show that the optimal indoortemperature set-up values for a room with low temperature forced convectionheating system and mixing ventilation are19℃,17℃and19℃in Copenhagen,Beijing and Harin, and the optimal indoor temperature set-up values for a roomwith low temperature radiant floor heating system and mixing ventilation are18℃,17℃and18℃in Copenhagen, Beijing and Harin.Based on the research of the design theory and application of low temperatureheating systems combined with outdoor air supply systems based on productivity,it is expected that this study could help to develop a universal approach to create ahealthy, comfortable, energy efficient and productive indoor thermal environmentand guide the design and operation and control of low temperature heating systemscombined with outdoor air supply systems in the new or used office buildings.