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Water Source Heat Pump Systems Operation Modes
 


A typical building has a perimeter with outside exposure that is directly affected by variable outdoor weather conditions and a core without outside exposure that is almost unaffected
by the weather. In order to understand the energy sharing benefits of a water-source heat pump system, the interaction of the loads in the core and perimeter zones must be analyzed for occupied periods (internal gains present) and unoccupied periods (temperature setback/setup and little or no internal gains) throughout the year. For illustration, the following are the main energy consuming operating modes

Summer Occupied

During hot weather with most or all units cooling, heat removed from the air is transferred to the water loop. An evaporative water cooler rejects the excess heat outdoors to maintain a maximum water temperature of approximately 90°F (32°C).

Winter Warm-Up

During recovery from night setback, most zones will require heating and will be extracting heat from the water loop.The boiler maintains the minimum water loop temperature according to a predetermined setpoint. The heat rejector is off. The warm-up period is typically one hour or less per day

Or only in very cold weather with most or all units heating is it necessary to add heat to the water with a water heater. This is done when the temperature of the water loop falls to 64°F (18°C). The amount of this heat is reduced any time one or more units are operating on cooling. The central water heater is never larger than two-thirds the size required in other systems but is usually less because of diversity.

Winter Occupied

Most core zones will require cooling because of the internal heat gains discussed previously. Most perimeter zones will require heating. Because heat is being simultaneously rejected into and extracted from the water loop, both theboiler and the heat rejector remain off much of the time. The inherent sharing of energy within the water loop minimizes boiler and heat rejector operation and provides maximum system efficiency.

At Partial loads

Water-Source Heat Pumps provide zone heating and cooling at the highest rated levels of efficiency.

The water loop inherently recovers much of the energy needed for heating the building, minimizing boiler use.

Water-loop heat pump systems operate efficiently under partial occupancy and at part-load conditions.

They also eliminate the double energy waste of zone reheat (cooling with subsequent reheating), which is common in many HVAC systems.

This all translates into reduced energy consumption and lower operating costs.

 
 
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