【正文】 affected in the same direction. . The ducts are assumed to be tight. If there were air leaking from the ducts, this result in a higher SFPvalue than the value given by the fan manufacturer. The SFP value can be measured when the system has been taken into operation. It is assumed that the exhausted air temperature is equal to the zone temperature. In reality there is a temperature gradient in the zone resulting in an exhaust air temperature higher than the zone set point temperature. Then, the recovered heat energy is underestimated in the energy use calculations. . The heat recovery unit is only used to heat the outdoor air and not to cool the outdoor air when the exhaust air temperature is lower then the outdoor temperature. . In practise, the supply fan is often located after the preconditioning units. Here, it is located before the cooling coil to simplify the calculations. If the supply fan were located after the cooling coil, the temperature after the cooling coil had to be lower due to the heating from the supply fan. In some cases, this would lead to increased energy use for condensation. . In the energy calculations no solar radiation is included. If solar radiation were present, the absolute calculated HVACenergy use would be affected. In the parison between the control strategies, the affection would be in the same direction and therefore the difference would be small. Solar radiation will not affect the supply air temperature optimization because from the system perspective there is no difference in solar gain or internal heat load. Therefore, solar radiation can be treated as a part of the internal heat load. . The efficiency of the boilet, hband the radiator system is set to be . . The temperature efficiency, ht of the heat recovery unit is assumed to be constant. The supply air flow and the exhaust air flow are equal.. The coefficient of performance (COP) of the chiller is assumed to be constant. The specific heat, cp=1000j/(kg℃), of air and the air density, r ( kg/m3),
are assumed to be constant. The density affects the fan power which would, in this case, vary approximately 1% if the density was treated as temperature dependent.. To simplify the model, the water pump energy used in the boiler and the heat recovery unit is assumed to be zero. Fan electricity, cooling electricity and heating energy are treated as equal.. Supply air temperature The supply air temperature, tSA, is limited by an upper temperature, tSAhigh, due to mixing ventilation and ventation effectiveness, and a lower temperature, tSAlow due to thermal fort: . Heat balance of the zone Eq. (1) describes the total load, Pload in a single zone that has to be cooled or heated by the system. Heating when the load is negative and cooling when the load is positive: Eq. (2) describes the cooling power, Pcooling provided by the supply air. The cooling power must be positive, meaning the supply air temperature, tSA, must be lower than the zone temperature, tzone: Eq. (3) is valid when the zone temperature set point and steady state condition are reached: . HVAC unit To meet the load in the zone, the HVAC unit must produce an air flow at a certain temperature. The radiator power, Prad is included in the HVAC unit power. The power, PHVAC, used to produce this is described in Eq. (4): The theoretical relationship between fan power, Pfan and air flow, q, is cubic (i = 3). However, in practice there are losses in the frequency converter and motor, and the fan efficiency is not constant. Therefore, a squared approach (i = 2) is more appropriate: Eq. (6) describes the air temperature after the supply fan. Pfan is the sum of supply and exhaust fan power and it is assumed that the supply fan electricity ((1/2)Pfan) converts into a rise in temperature of the supply air: The boiler and the heating coil are used to increase the supply air temperature after the heat recovery unit. As far as the supply air temperature is higher than the maximum air temperature after heat recovery, it does not matter in energy perspective whether radiator or boiler is used to heat the zone : The power saved by the heat recovery unit, PHR, is described in Eq. (8): The temperature efficiency of the heat recovery unit, is expressed in Eq. (9). It is assumed that it is not air flow dependent: Perfectly mixed air is assumed in the zone, that results in Eq. (10): If the calculated supply air temperature is higher than the highest supply air temperature, then Eq. (11) is used to calculate the radiator power input (Prad 0): The power input to the chiller, PCM, described in Eq. (12): When the supply air is cooled below the dew point temperature, there will be an extra energy loss in the chiller for condensation. Here, it is assumed that the condensed mass is equal to the outdoor moisture content minus the saturation moisture content at the supply air temperature. The power used to decrease the temperature of the condensed water is relatively small and therefore neglected. To find a manageable expression for the condensed power, a linear regression analysis of the moisture content dependent on the saturation temperature is done. The analyzed range was between 12 and 26 .C. The regression analysis results in Eq. (13): The constant, a is gH2O/m3 .C and the correlation coefficient is .The condensed mass when decreasing the temperature from tsat to tSA is expressed in Eq. (14), where b is reduced: The cooling power input caused by condensation is expressed in Eq. (15): Based on the equations given, the operation of the HVAC unit can be divided into four different cases.附錄B變流量系統(tǒng)中送風(fēng)溫度的優(yōu)化設(shè)計(jì)蘭德大學(xué)，物理樓byggnadsfysikLTH，118信箱，蘭德22100，瑞典摘要在以100%室外空氣送風(fēng)的變空氣容積系統(tǒng)（VAV）中，當(dāng)送風(fēng)溫度一定時(shí)，房間所需的制冷量與空氣的流動(dòng)情況有關(guān)。在有VAV控制的空間中，當(dāng)熱負(fù)荷增加時(shí)空氣流動(dòng)也會(huì)隨之增加。（見(jiàn)圖1）在第一節(jié)中，建筑物房間被看作是具有同一溫度狀態(tài)，同一流動(dòng)狀態(tài)的制冷空間。假設(shè)墻壁內(nèi)表面是完全絕熱