Retrofit

Retrofitting Strategy	De-centralised chilled water distribution system for equipment with different chilled water operation requirements
	Some spaces have a stricter requirement on chilled water supply temperature to their premises such as data centres. While other general spaces such as general offices usually only require the air-conditioning system to satisfy their cooling load needed instead of satisfying the requirement of chilled water supply temperature. Some buildings may be cooled by chilled ceiling which needs a higher chilled water supply temperature. Buildings having only one chilled water supply system will require the supply temperature set to the minimum temperature required by the most critical terminal device for the whole building. The building can have two separate chiller and riser systems, one that is set for the most critical device for temperature requirement and the other one that can have a more flexible temperature setting. The latter can enable the supply chilled water temperature to be raised to just satisfy the cooling load. With a higher supply chilled water temperature setting, the chillers can run at a higher efficiency.
	Consideration
	More space is needed to accommodate the extra riser and accessories. Rearrangement of the chilled water pipes is required. At least two chiller sets will be required and may add cost for services. Installation of power meter, temperature sensors, and flowmeter or differential pressure sensors for monitoring the power, cooling energy and COP of chiller (Figure 1).
	Estimated Saving
	(1/COP_CH_PRE – 1/COP_CH_POST) * (xQBLDG) OPHR,yr Where x is the percentage of QBLDG operate at different TCHWS (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)] assume DTCHW_PRE = DTCHW_POST OPHR,yr = hr/dayday/wk52 Please click HERE to view the list of terminology.