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DOAS with Heat Recovery for AHU

asked 2018-11-08 08:34:12 -0500

zahro gravatar image

updated 2018-11-12 19:25:12 -0500

Hi, I am trying to model AHU with a heat recovery system in energy plus with DOAS feature. I am trying to look at the impact of my heat recovery effectiveness both sensible and latent to my size of DOAS cooling coil rate. However, it seems like the heat recovery effectiveness did not bring much impact to my DOAS cooling coil rate. For sizing system, here said that the sizing did not take into account the heat recovery, and there should be a difference in the annual simulation result. However, when I tried to have two difference efficiency (0.3 and 0.75) both the sizing result and the annual simulation result don't change. image description

When I take a look at the energy result, there is a difference in heat recovery total energy for efficiency 0.3 and 0.75. For the efficiency of 0.3 = image description

For the efficiency of 0.75 = image description

The total electric cooling energy for the building is the sum of heat pump electric energy and DOAS electric energy. Both DOAS and VRF system have the same system availability schedule, but why there is a big difference in energy result but not in cooling coil rate?

This is the sizing:system description that I used in my model. image description

image description

Now, I tried to understand how it works in other simulation software, and the DOAS sizing is changed when I change the heat recovery efficiency. As explained here, the impact of heat recovery in Energy plus is not taken into account for the DOAS coil sizing. The software did the separate calculation with E+ by taking the condition of the air after the heat recovery coil at each time-step and sizing the heating and cooling coils in the air handling unit based on that condition rather than on the pure outside air condition.

I took a look at the system node temperature from E+ result, and found out that there is a difference DOAS cooling coil inlet temperature when I changed the heat recovery effectiveness. However, there is no change in the DOAS cooling coil capacity as explained above. I quite do not understand about the sizing calculation when there is DOAS with heat recovery system and how to model the AHU system correctly in Energy Plus.

I would be grateful to have any help for solving my problem. Thank you.

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What inputs do you have selected for sizing your air loop? (Sizing System object)

mdahlhausen gravatar imagemdahlhausen ( 2018-11-09 13:36:54 -0500 )edit

I have edited my question with the sizing: system input description for my model and I added several additional questions regarding the DOAS system with heat recovery in Energy Plus. I would be grateful if you could help me solve the problem.

zahro gravatar imagezahro ( 2018-11-11 10:05:56 -0500 )edit

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answered 2018-11-15 13:25:02 -0500

Looking at the table outputs, the cooling coil load is lower with 0.75. Output variables are all defined in the Input Output Reference. The variables in the above tables are defined in the section titled "System Loads Outputs":

The following two variables report the heat energy that system components (including packaged equipment, fans, main coils, reheat coils, humidifiers, desiccant dehumidifiers, evaporative coolers and heat exchangers) add or remove from the air loop.

Air System Total Heating Energy and Air System Total Cooling Energy

And further down.

Air System Cooling Coil Total Cooling Energy, Energy removed from air loop by Cooling Coils (Joules)

Air System Total Cooling Energy should be nearly the same with any HX effectiveness. Air System Cooling Coil Total Cooling Energy is lower with higher HX effectiveness.

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Asked: 2018-11-08 08:34:12 -0500

Seen: 295 times

Last updated: Nov 15 '18