School of Environmental Science and Technology, Tianjin University Heat Efficiency of a Plate Enthalpy Exchanger and its Energy Saving Performance in a Residential Building
Dr. Junjie Liu
天津市南开区卫津路92号 ContentContent
• Background • Calculation in Weight Coefficient of Enthalpy Exchanger Efficiency • Analysis of weight coefficient in diverse areas and situations • Calculation of the saved energy by using ERV in winter with variety conditions • Conclusion and Future Work BackgroundBackground
• For meeting the demand of indoor air quality and public Enthalpy Exchanger health, HVAC system has to bring in large quantity of fresh air, and take out exhaust air at the same time.
• It can reduce part of the energy handling fresh air, decrease HVAC unit load, and make system more economical by fresh air pre-handling with the energy recovered from exhaust air. BackgroundBackground
• made up of sensible heat and latent heat • cannot get enthalpy efficiency simply from arithmetic mean of sensible heat efficiency and latent heat efficiency For the weighted difference between sensible heat exchange and latent heat exchange in enthalpy exchange Calculation in Weight Coefficient Calculation in Weight Coefficient
• 3 kinds of efficiency under summer condition
− TT − dd − hh η = ,, ofif η = ,, ofif η = ,, ofif s L t − hh − TT ,, iexif − dd ,, iexif ,, iexif η η ηs ——sensible heat L ——latent heat t ——enthalpy efficiency efficiency efficiency d h ,if ——fresh air inlet T ——fresh air inlet ,if ——fresh air inlet ,if temp，K humid，kg/kg enthalpy ，kJ/kg h ——fresh air outlet T ,of ——fresh air outlet d ,of ——fresh air outlet ,of enthalpy，kJ/kg temp，K humid，kg/kg h ——exhaust air ,iex ——exhaust air T ,iex ——exhaust air d ,iex inlet temp，K inlet humid， inlet enthalpy， kg/kg kJ/kg Calculation of Enthalpy
= ,dp tch + 2500( + ,sp )dtc
h ——enthalpy of humid air ，kJ/kg c ,dp ——dry air specific heat capacity at constant pressure， 1.005 kJ/(kg·K) c ,sp ——vapor specific heat capacity at constant pressure ， 1.84 kJ/(kg·K) t ——temperature of humid air ，℃ d ——humidity of humid air，kg/kg
,sp tc is much smaller than 2500, so it can be omitted within error less than 5%. We can get:
= ,dp + 2500dtch Calculation in Weight Coefficient
− TT ,, ofif + − dd ,, ofif )(2500)(005.1 ηt = TT ,, iexif +− − dd ,, iexif )(2500)(005.1
Divided by − ⋅ − ddTT ,,,, iexifiexif )()( 005.1 2500 η s + η L − − TTdd + BA ηη η = ,, iexif ,, iexif = s L t 005.1 2500 + BA + − − TTdd ,,,, iexifiexif
005.1 2500 A = B = − dd ,, iexif − TT ,, iexif Calculation in Weight Coefficient the weight coefficient as follows: A B C = C = s + BA L + BA 005.1 A = ——weight coefficient of sensible heat efficiency Cs − dd ,, iexif 2500 C ——weight coefficient of latent heat efficiency B = L − TT ,, iexif
So the relation between 3 kinds of efficiency：
η = η + CC η LLsst Analysis of weight coefficient in diverse areas and situations AnalysisAnalysis ofof weightweight coefficientcoefficient inin diversediverse areasareas andand situationssituations underunder summersummer conditioncondition
Most areas in China：Sensible Heat Efficiency Situation in the Northwest of China Need humidification Sensible heat exchanger better than enthalpy heat exchanger underunder winterwinter conditioncondition Sensible Heat Efficiency > Latent Heat Efficiency Comparing in Weight Coefficient of Efficiency Summer Winter underunder winterwinter conditioncondition Sensible Heat Efficiency > Latent Heat Efficiency CalculationCalculation ofof thethe savedsaved energyenergy byby usingusing ERVERV ERV Air Handling Process GeometricGeometric datadata ofof thethe apartmentapartment andand 3D3D modelmodel byby EnergyPlusEnergyPlus CalculationCalculation ofof savedsaved energyenergy byby ERVERV Saved Energy Percentage by ERV on Different Enthalpy Efficiency in Beijing CalculationCalculation ofof savedsaved energyenergy byby ERVERV Outdoor Enthalpy [J/kg] Saved Energy Percentage 60000 25% 50000 40000 20% 30000 Beijing Beijing Shanghai 15% 20000 Shanghai Harbin Harbin 10000 Guangzhou 10% Guangzhou Kunming Kunming 0 Indoor Enthalpy er ry ry -10000 b a a ch 5% m tober e ru Mar c c b O e Janu Fe -20000 November D 0% -30000 October November December January February March More difference between indoor and outdoor enthalpy, the higher percent of energy is saved. But it’s unsuitable to operate ERV on Oct. in Guangzhou, for ERV could hardly save any energy at that time. CalculationCalculation ofof savedsaved energyenergy byby ERVERV Saved Energy Percentage Equipments Energy Consumption[J] 25% 2.50E+08 20% 2.00E+08 15% 1.50E+08 50W 50W 100W 100W 150W 10% 150W 1.00E+08 no ERV 5% 5.00E+07 0% 0.00E+00 October November December January February March October November December January February March energy consumption by fan is the most part of all equipments energy consumption when using ERV, and the equipments energy consumption is greatly influenced by fan power. However, total energy consumption using ERV is evidently lower than one without ERV. For the different effect of saving energy under variety fan power conditions, and it is important to improve in fan efficiency for better energy saving. CalculationCalculation ofof savedsaved energyenergy byby ERVERV Saved Energy Percentage With Different Ventilation Times[h-1] of Fresh Air in Beijing 35% 30% 25% 20% 0.5 0.75 15% 1 10% 5% 0% October November December January February March During the rising of ventilation flow (fresh air flow rate), saved energy percentage is accordingly increasing. However, there is also a great increase in total energy consumption due to more fresh air load. It is significant to find a balancing point between ventilation time (indoor air quality) and total energy consumption. ConclusionConclusion • The equation of weight coeffient is available in most areas of China for calculation and analysis, except several cities (Xinjiang, Tibet and Qinghai) in Northwest. • The weight coefficient calculation under winter condition be average value of sensible and latent 0.690 and 0.310 • The weight coefficient calculation under summer condition be average value of sensible and latent 0.358 and 0.642. ConclusionConclusion (cont(cont’’d)d) • In most areas, enthalpy efficiency of enthalpy exchanger mainly depends on sensible heat efficiency in winter and on latent heat efficiency in summer. • Under both summer and winter condition, weight coefficient of sensible heat efficiency goes down with outdoor temperature’s down while the weight coefficient of latent heat efficiency goes up, but the trend is milder in winter. ConclusionConclusion (cont(cont’’d)d) • The energy saving performance of the ERV is related to the outdoor climatic condition, the enthalpy efficiency, fan power and ventilation times. • The larger the indoor-outdoor enthalpy difference, or the higher at enthalpy efficiency, or the lower fan power, or the more ventilation times, the more energy can be saved. However, it will also cost more in high level heat exchanger, high performance fan and more energy consumption due to high frequency ventilation. ConclusionConclusion (cont(cont’’d)d) • To improve saving performance, more efficient enthalpy exchange materials and more powerful fans must be explored so as to reduce the price of it, and reasonable ventilation times as well as proper operation period according to local climate should also be carefully considered. THE END Thank you!! Contact us: [email protected] www.airfilter.org.cn Questions?