Andrew Corney
Overview
This template generates a central DOAS air handling unit that provides a constant volume of conditioned outside air to all zones. It also generates water source heat pump zone units in each zone.
Application
This template system only applies to water source heat pump system units
Air Handling Unit (AHU) – Return Air
The table below describes the key properties of the AHU for this system where there is return air:
|
AHU Feature |
Default |
Extent of user-control |
|
Airflow Rate |
Constant area-weighted rate for all zones |
Can change constant |
|
Supply Air dry bulb Temperature |
Constant with defaults as follows: |
Can change constant value |
|
Supply Air Temperature Reset Controls |
None |
No control |
|
Supply Air Dew Point Controls |
Constant with defaults as follows: Min: -5 C or 23 F Max: 13 C or 55.4 F |
None |
|
Supply Air Humidification Controls |
Via Min Supply Air Dew Point Control |
None |
|
Peak Fan Power |
3.5 W/(L/s) or 1.65 W/cfm |
Can control peak load |
|
Fan Curve |
Standard ASHRAE. |
No control |
|
Outside air configuration |
100% outside air |
No control |
|
Return Air Rate |
100% of air assumed to be returned for heat recovery |
No control |
|
Heat Recovery Efficiency |
Sensible and Latent effectiveness available. Default is 50% sensible and 0% Latent. |
User can change sensible and latent effectiveness |
|
Cooling Coil |
Direct Expansion coil post heat recovery |
No control |
|
Heating Coil |
Hot water coil post chilled water coil |
Can change to electric coil or direct gas |
|
Frost Coil |
Electric coil pre-heat recovery |
Can change to hot water |
|
Frost Coil Setpoint |
Setpoint for coil – default is 2C |
Can Change default |
Zone WSHP Units
Zone WSHP units are self-contained heat pump fan coil units that are connected to the condenser water loop. Zone units absorb or reject heat to the condenser water loop depending on if they are in the heating or cooling mode.
The table below describes the key properties of the zone level WSHP units for this system:
|
Fan Coil Unit Feature |
Default |
Extent of user-control |
|
Heating Coil Type |
Heat pump |
Can change to electric or gas coil |
|
Supplemental Heating Source |
Hot water |
Can change to electric coil |
|
Cooling Type |
Direct Expansion |
No control |
|
Fan Coil Motor Type |
On/Off |
No control |
|
Peak Fan Power |
0.64 W/(L/s) or 0.3 W/cfm |
Can control peak load |
|
Fan Curve |
Constant Volume Fan |
No control |
|
Supply Air Temperature - Heating |
Constant for all zones (35C / 95F) |
User can change constant |
|
Supply Air Temperature - Cooling |
Constant for all zones (13C / 55.4F) |
User can change constant |
|
Demand Control Ventilation |
None |
None |
|
Dehumidification Load |
Air dehumidified to achieve the cooling setpoint at 60% Relative Humidity in the zone |
None |
Central Plant Configuration
The base case option is assumed to have a central plant that provides heating hot water to the AHU and zone.
|
Central Plant Feature |
Default |
Extent of user-control |
|
Heating Hot Water Source |
Natural Gas |
Can change to electric boiler |
|
Boiler Peak Efficiency |
Assumed to be 0.9 |
Value can be changed |
|
Boiler Performance Curve |
No Control |
|
|
Supply and Return Temperatures – hot water |
80/70 C or 176/158 F |
User can control |
|
System losses |
Constant loss of 15% |
User can control loss rate only. |
|
Peak Pumping Energy |
1.32 W/(L/s) or 21 W/gpm |
No control |
|
Pump Efficiency Controls |
Variable Speed Drives |
No control |
|
Efficiency Curve for Variable Pumping |
No control |
|
|
Pumping Configuration |
Primary Only |
No control |
|
Condenser Water Source |
Cooling Tower |
No extra options |
|
Cooling Tower Efficiency |
245.7 W/(L/s) or 15.5 W/gpm |
Value can be changed |
|
Supply and Return Temperatures – condenser water |
29/35 C or 84.2/95 F |
User can control |
|
System losses |
Constant loss at 5% |
User can control loss rate only. |
Could you please add a simple sketch of an exemplary System architecture and describe which components are modelled (i.e adiabatic pipes etc.) ?
Thanks!!
I agree with Philip
Could you add some detail around the "Ground Heat Exchanger"?
Why have the moderators not responded? These are good questions.
Hi Rob,
Thanks for bringing my attention to this. April who originally wrote this has moved on and I guess at the time she assumed these questions were reaching other people.
I'll see if we can find some diagrams to add to this information - I agree they would be helpful.
best,
Andrew