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E+, HVAC templates VRF and DOAS, relations between outputs

asked 2018-10-10 01:57:51 -0500

Mantra gravatar image

updated 2018-10-10 07:30:46 -0500

On E+, I am using a HVAC templates vrf and a hvac templates DOAS with heat recovery and cooling coil.
I have my output "VRF HEAT PUMP TOTAL COOLING RATE", I would like to know what I need to sum to get this cooling capacity.
I have this system :
image description

I have tried many things, like set the exchanger efficiency at 1 or set the length of piping at 0.01m to see easily a relation but I cant find my VRF cooling capacity.
As output, I have :
- ZONE VRF AIR TERMINAL TOTAL COOLING RATE,
- FAN HEAT GAIN TO AIR (DOAS and VRF),
- COOLING COIL TOTAL COOLING RATE (coil DOAS and coil VRF),
- HEAT EXCHANGER TOTAL COOLING RATE
- VRF HEAT PUMP TOTAL COOLING RATE.
Is there is any relation between all these outputs ? If yes, could you help me ? I know that there are the piping loss as well to take into account but its impossible to get with this templates.

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answered 2018-10-10 11:25:51 -0500

updated 2018-10-10 11:29:55 -0500

The VRF Heat Pump Total Cooling Rate = sum of Cooling Coil Total Cooling Rate plus piping losses.

The other reports you mention, fan heat gain to air and heat exchanger total cooling rate affect the zone load but are incorporated into the Cooling Coil Total Cooling Rate report because the coil will need to meet any load added to the zone. The final report, Zone VRF Air Terminal Total Cooling Rate simply reports what the VRF terminal unit is adding to the zone, whether or not the coils are operating.

Since the Zone VRF Air Terminal Total Cooling Rate represents the cooling provided to the zone, this report variable should match the Zone Predicted Sensible Load to Cooling Setpoint Heat Transfer Rate variable that shows what the zone load is. If they match, the zone will meet the zone thermostat set point temperature.

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Ok thank you. About the DOAS cooling coil, what is it role in E+ ?
I thought, it was to cool down the outdoor air or mixed air but with or without the heat exchanger, the DOAS cooling coil rate doesnt add up to the vrf heat pump total cooling rate. When I set some parameters, just the values of my vrf cooling coil and my vrf heat pump total cooling rate vary. I know how work the system in real but in E+, I dont really understand how work the heat exchanger and the cooling coil for a VRF and a DOAS. The results I get are not really clear for me

Mantra gravatar imageMantra ( 2018-10-11 04:47:25 -0500 )edit

When you identify a cooling coil as DOAS it means that coil sees 100% outdoor air as the entering conditions and, more importantly, the design coil air flow rate can be lower (W/m3/s [cfm/ton]) than a normal coil since DOAS coils may have lower air flow rate to better dehumidify. In your simulation the VRF and DOAS are independent but do serve the same zone. The DOAS Cooling Coil is not connected to your VRF system. Look at the Model Room VRF Cooling Coil to compare to the VRF system output. You can use a text editor to edit the *.expidf and search for coil names or inspect the inputs.

rraustad gravatar imagerraustad ( 2018-10-11 07:39:07 -0500 )edit

The *.expidf is the file that is created from HVACTemplate objects and is the one actually used to run the simulation.

rraustad gravatar imagerraustad ( 2018-10-11 07:39:50 -0500 )edit

Ok I see, so I guess, to have the total cooling capacity of my room and my VRF, I need to add this DOAS cooling coil rate to the vrf cooling coil ? Because in my project, my vrf will be connected to the doas coil.
I have seen For the electric energy in the main summary, E+, add the 2 electric energy to have to total electric energy.

Mantra gravatar imageMantra ( 2018-10-12 05:54:21 -0500 )edit

To get the total delivered cooling load to the room, add VRF + DOAS cooling coils. To get VRF Heat Pump Total Cooling Rate, only use Model Room VRF Cooling Coil Total Cooling Coil Rate (these 2 should match except for piping losses). To get total outdoor air total cooling coil rate, only use DOAS Cooling Coil Total Cooling Coil Rate. To get the total cooling load of the room without outdoor air, use Zone Predicted Sensible Load to Cooling Setpoint Heat Transfer Rate. Yes, total electricity is the sum of both systems. So it depends on what information you want to know which variables to use.

rraustad gravatar imagerraustad ( 2018-10-12 06:57:25 -0500 )edit

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Asked: 2018-10-10 01:57:51 -0500

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Last updated: Oct 10