Many buildings have large internal zones that require cooling only during occupied hours, or cooling, year-round due to internal heat gains. The chiller condenser water heat is recovered, instead of being rejected to the outside, and used as a heat source for a water-source heat pump system serving the perimeter spaces.
The closed water loop provides condenser water to the interior zone cooling units, picking up the heat normally rejected to a cooling tower, and transferring it as the heat source (evaporator load) for the perimeter zone heat pumps. This substantially increases the coefficient of performance (COP) and lowers the operating cost of the heat pumps over conventional air-source heat pumps. The water loop temperature is typically maintained between about 65 and 90° F and therefore piping can be uninsulated. Loop circulation is typically between 2 to 3 gpm per ton of cooling capacity.
During peak winter conditions when the air source heat pump cool the loop below 65° F, a boiler (electric, gas, oil) is used to maintain the 65° F temperature. During peak cooling conditions when all or most of the units are rejecting heat to the loop and its temperature tends to rise above 90° F, a closed-circuit evaporative cooler is used to reject the unneeded heat. As the loop temperature rises, the dampers on the tower (evaporative cooler) open to allow gravity circulation over the loop water coil. If the loop temperature continues to rise, the water spray circulator is turned on. If the loop temperature still rises, then the fans are turned on for full capacity performance.
Closed water loop water source heat pump systems have these key advantages:
Meet Construction Budgets
Increase Leasable Space
Lower Operating Costs
Improve Cash Flow
There are also specific advantages for Architects, Owner/Developers, and Consulting/Design Engineers.
Advantages for Architects:
Aesthetics - Most equipment is not visible. Roof is cleaner with less possibility of leaks.
Flexibility - The system can be subdivided or expanded into new zones to fit building remodeling or additions easily and inexpensively.
Ceiling height to floor can be smaller and building height lower.
Smaller mechanical rooms (50% or less in new construction).
Less duct shaft space (saves on fire dampers) than air systems.
Small building allows construction dollars to be used for other items.