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Modeling Run-around Loop Heat Recovery in EnergyPlus

asked 2015-03-05 11:53:16 -0500

updated 2015-11-09 13:26:56 -0500

What is the best way to model a run-around loop heat recovery system in EnergyPlus? I see HeatExchanger:AirToAir and HeatExchanger:Desiccant, but don't see a dedicated model for a run-around loop system.

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answered 2015-03-05 12:25:24 -0500

I'm currently working on an EnergyPlus model that simulates run-around loop heat recovery in a laboratory building. The system recovers heat from the lab exhaust stream, which is assumed to run at constant flow. I've created a plant loop (with propylene glycol solution fluid properties), served by district cooling and heating energy sources and connected to cold and hot water coils on the AHU. To adjust the available capacity at varying outside conditions, I'm controlling the loop setpoint temperature with an EMS routine that sets the fluid temperature based on outdoor air temp along a curve calculated from the design effectiveness (using the same equation as air-to-air hx sensible effectiveness). The routine also enables or disables the pump above/below OAT setpoints. Zone exhaust fans account for the exhaust energy, the loop pump accounts for the pumping energy, and the 'district' energy will be neglected in post-processing as recovered.

I'm not sure if this is the 'best' method, but in theory it seems to capture the available capacity between the exhaust air temperature and outdoor air temperature. It's still a work in progress, but I will update this answer as I ensure that everything is working properly.

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That's an interesting method. I was hoping for something a bit more repeatable, but may give this a try. I'm a bit surprised such a common system doesn't have a model yet in EnergyPlus... It's good to see that others are trying to model laboratory exhaust, also.

jmcneill gravatar imagejmcneill ( 2015-03-06 10:34:35 -0500 )edit

Seems a great work! I would like to know the update. My opinion is that if you want to preheat or precool outdoor air and need mostly sensible heat for that then the runaround loop is the way to go. If you have a large latent load in your outside air, then you should consider the enthalphy wheel. I'm learning energy plus and I'm reading how to use rundaround loops for cooling coils because I know I will use it a lot in my climate, which is hot and humid all the year.

Carlos Vazquez gravatar imageCarlos Vazquez ( 2015-03-17 10:56:16 -0500 )edit

Great work. If you knew the capacity of the heat recovery system over time (from hourly data), you could simulate a simple plant loop with district heating, heat recovery pump (as designed), and heat recovery coil (as designed). Input the nominal capacity of district heating to maximum heat recovery capacity and input the capacity fraction schedule of district heating to a hourly schedule. Finally, input the setpoints of the loop and coil as designed. Heat recovery for cooling could be similar except using district cooling instead of district heating. Comments?

cjcfromslc gravatar imagecjcfromslc ( 2015-05-07 17:57:11 -0500 )edit

@Eric Ringold: thanks for sharing the approach, sounds like a practical way to go about it. Is it possible for you to share the idf you created to be used by others?

Amir Rezaei gravatar imageAmir Rezaei ( 2015-10-20 10:37:32 -0500 )edit

@Amir Rezaei the work I described above was done for a previous employer that I'm no longer with, so I'm not in a position to share IP. I'll probably be revisiting this method for current project soon, I'll try to update this page with some more details as it is refined.

Eric Ringold gravatar imageEric Ringold ( 2015-10-21 10:50:07 -0500 )edit

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Asked: 2015-03-05 11:53:16 -0500

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Last updated: Mar 05 '15