WSHP system with Central Outdoor-Air System

Typically used in hotels and high end residential buildings. Central Outdoor-Air Handling Unit provides 100% of Outside Air to the zone meaning all air that is going through the unit is only the Outside Air, there is no mixing with the return air. All exhaust air from the zones goes to the Heat Recovery unit where Outside Air that we are introducing to the building is preheated or precooled depending on the season.

If heat recovery effectiveness is zero that practically means that DOAS doesn’t have the heat recovery. If “Design Air Flow” for the “Central Outdoor-Air Handling Unit” is zero that practically means that there is no “Central Outdoor-Air Handling Unit”.

User decides on how much outside air will be supplied to the building. This is done via “Design Air Flow” slider.

Water Source Heat Pump zone units are connected to the condenser water loop that they use to either reject heat (cooling mode) or absorb heat (heating mode). WSHPs are basically mini water-cooled DX units. Condenser water loop is connected to the cooling tower and boiler. Their job is to maintain the temperature range in the loop between 20C and 30C. When all WSHPs are in the cooling mode, all units are rejecting heat to the loop and the loop temperature is rising. To prevent the rise of the condenser water loop temperature above 30C, cooling tower is used to lower (cool down) the temperature of the loop. In heating mode is opposite, all units are absorbing heat from the loop and boiler’s job us to make sure that the temperature of the water in the condenser water loop doesn’t drop below 20 C. In the so called mixed mode, some units are in the cooling and some are in the heating mode which can lead to the situation that cooling tower and boiler will operate very little or not at all since the heat of absorption and rejection will balance the temperature of loop.


Default values:

  • Condenser Water Pump power: 21 W/gpm or 1.32 W/(L/s)
  • -Condenser water loop temperature between: 68F and 86F (20C and 30C)
  • -Cooling Tower Fan with VSD
  • -WSHP zone unit Fan Power: 0.2 W/cfm or 0.095 W/(L/s)
  • -DOAS Fan Power: 0.9 W/cfm or 0.4 W/(L/s)
  • -DOAS heat recovery type: Enthalpy



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