Trane SYS-APM001-EN manual Sidestream with alternative fuels or absorption, Production, Recovery

Chilled-Water System Variations

Referred to as “distribution sidestream,” an alternative location is to apply the chiller at the air handler that requires reheat. The heat recovery chiller can cool either the supply or return chilled water. If only a small amount of heating is needed, this may be accomplished with a water-to-water heat pump.

Sidestream heat recovery

A similar situation occurs if a heat-recovery chiller is placed in this sidestream position24 (see Figure 46). This chiller may be equipped with a heat recovery condenser or it could be a standard, single-condenser chiller operating as a heat pump in a heating control mode. The chiller may not be capable of cooling water to the system supply temperature. That is unimportant with this configuration. Think of the machine as a heater instead of a chiller. Its primary function is heating, and cooling is a beneficial by- product. The passing return-chilled-water stream appears as an infinite heat source to the heat recovery chiller. The chiller only cools its evaporator water enough to satisfy the heating demand. This avoids the control predicament of deciding how to reject surplus condenser heat when the cooling and heating loads of a chiller do not strike a perfect heat balance.

Figure 46. Heat recovery chiller in sidestream position

50.2°F

[10.1°C]

Off
40°F	Chilled
[4.4°C]	Water
	Production
900 gpm [56.8 L/s]
40°F [4.4°C] 75 gpm

51.2°F	Bypass Line
[10.7°C]
	42.7°F [5.9°C]
		Heat
		Recovery
		Chiller
56°F
[13.3°C]	300 gpm [18.9 L/s]

Chilled

Water

Distribution

825gpm

[52 L/s]

Sidestream with alternative fuels or absorption

An absorption chiller may be applied in a sidestream location. This allows the chiller to be loaded whenever utility rates make it beneficial. It also ensures that the absorption water chiller receives the warmest entering-water temperature, allowing it to operate more efficiently and produce more cooling.

SYS-APM001-EN Chiller System Design and Control 75