Retrofit

Retrofitting Strategy	Installation of indirect evaporative cooling System (IEC) for pre-cooling of primary fresh air with exhaust air
	Indirect evaporative cooling involves two air streams – the air supplied to the indoor spaces and a secondary stream that is exhausted outside. In operation, an indirect evaporative process cools air or water on one side of an impermeable heat-exchange surface such as a thin plastic plate or tube. The wet side cools the dry side without adding moisture (because there is no direct contact between the water and the airstream to be cooled).
	Consideration
	The exhaust air needs to flow back to the heat exchanger of the PAU. The air path or ducting needs to be designed. Needs to have central exhaust and PAU on each floor.
	Estimated Saving
	Waterside (PAUàFAF): 1/COP_CH (QBLDG_PRE – QBLDG_POST)OPHR,yr Waterside (VSD CWP for IECU): SkW_CWP_POSTOPHR,yr Where (COP_CH_POST – COP_CH_PRE)/ COP_CH_PRE = 1.25% per 1°C increase of TCHWS COP_CH_POST = [1.25%(TCHWS_POST – TCHWS_PRE) + 1]COP_CH_PRE COP_CH = 0.605COP_CH_SM + 0.395COP_CH_WN COP_CH_SM = (COPa_SM + COPb_SM)/2; COP_CH_WN = (COPa_WN + COPb_WN)/2 QBLDG = 0.605[0.77(0.88NCH_SMQCH_SM + 0.12NCH_WNQCH_WN)] + 0.395[0.596(0.184NCH_SMQCH_SM + 0.816NCH_SMQCH_SM)] SkW_CWP_POST = 0.605LF_SM(0.88NCWP_SMkW_CWP_SM + 0.12NCWP_WN* kW_CWP_WN) + 0.395* LF_WN(0.184NCWP_SMkW_CWP_SM + 0.816NCWP_WNkW_CWP_WN) For CSD: LF_SM = LF_WN = 1; For VSD: LF_SM = 0.795, LF_WN = 0.562; For EC or DC-motor: LF_SM = 0.71, LF_WN = 0.38 OPHR,yr = hr/dayday/wk52 Airside: (AHUàIECU) (SkW_AHU_PRE – SkW_IECU_POST) OPHR Where S kW_AHU_PRE = (0.605LF_SM,PRE + 0.395LF_WN,PRE )NAHUkW_AHU SkW_FCU_POST = (0.605LF_SM,POST + 0.395LF_WN,POST)NIECUkW_IECU For CSD: LF_SM = LF_WN = 1, For 3-speed: LF_SM = 0.882 , LF_WN = 0.717 For VSD: LF_SM = 0.795, LF_WN = 0.562; For EC or DC-motor: LF_SM = 0.71, LF_WN = 0.38 OPHR = hr/dayday/wkwk/yr Please click HERE to view the list of terminology.