[Bldg-sim] Energy recovery with wheel and runaround loop coil?

[Bishop, Bill]

Keith,
Thanks for your suggestions! I like your idea of putting the runaround coil first to prevent wheel frosting, and your idea of putting the wheel and coil in parallel (though that would eliminate the benefit of preventing wheel frost). The AHU as currently designed has bypass dampers for economizer mode and having the wheel and coil in parallel would add even more complexity, but I'll run the idea by the engineer.
Yes, the glycol preheat coil is to ensure 55F mixed air temperature.
Thanks,
~Bill

From: Keith Swartz [mailto:KSwartz at seventhwave.org]
Sent: Friday, December 11, 2015 5:33 PM
To: Bishop, Bill <bbishop at pathfinder-ea.com>; bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] Energy recovery with wheel and runaround loop coil?

Bill,

I think there is some advantage to have the runaround coil before the wheel to reduce frosting. (Think of the processes on a psychrometric diagram.) I think this arrangement will be easier to control too. Let the less-controllable runaround loop do its thing first and then use the more-controllable wheel to finish the job without overheating.

What is the purpose of the glycol preheat coil? Is it for frost protection or to bring the temperature up to 55F when needed? If it's for temperature control then I would put it downstream of the energy recovery devices. If it's for frost protection on the wheel then I would put it upstream of the wheel and downstream of the runaround coil.

The air imbalance between outside air and exhaust air is pretty significant. What do you think about putting the wheel and runaround coil in parallel, splitting the outside air stream so that the flows through each are more balanced? The wheel could be smaller then, which could make room for the runaround coil.

Keith Swartz, PE | Senior Energy Engineer
Seventhwave | Madison.Chicago.Minneapolis
608.210.7123 seventhwave.org

From: Bishop, Bill [mailto:bbishop at pathfinder-ea.com]
Sent: Friday, December 11, 2015 1:06 PM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] Energy recovery with wheel and runaround loop coil?

I'd appreciate comments on how to maximize the energy savings from using a runaround loop coil and energy recovery wheel in series.

I'm modeling a lab HVAC air handler that has an energy wheel and return/exhaust fan at the air handler but where 1/3 to ½ of the OA is exhausted elsewhere (a dedicated fume hood exhaust system). The designer is considering an option for additional heat recovery via a runaround loop with glycol coils at the fume hood exhaust and the air handler OA stream. This is in a heating-dominated climate (CZ 6A) and the SAT will be 55F.


-        Any thoughts on how to arrange the coils in the OA stream, which will also include a glycol preheat coil and a CHW coil? (Runaround coil -> wheel -> preheat coil -> CHW coil?)

-        How to control the system? (Activate and modulate the wheel first; activate the runaround loop when OAT drops below the point that wheel can maintain the mixed air temperature?)

-        I assume the pumping power for the runaround loop would be higher than the motor power for rotating the wheel.

Thanks!

William Bishop, PE, BEMP, BEAP, CEM, LEED AP | Pathfinder Engineers & Architects LLP
Senior Energy Engineer

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