[Bldg-sim] Air mixer for fresh air loop in E+?

[Timothy Moore]

Aaron,

A cooling coil with heat exchanger (heat wheel, enthalpy wheel, counter-flow heat exchanger, heat pipe, etc.) connected immediately upstream and/or downstream of the coil as you have described to assist in cooling and/or to provide “free” reheat immediately following sub-cooling for dehumidification can readily be modeled in the ApacheHVAC module of the IES Virtual Environment. In the example below, I’ve added the damper set highlight in red to show how your mixing damper downstream of the cooling coil can be explicitly modeled; however, this is necessary only if you want to query air network node results for the inputs for this damper. A functionally equivalent bypass damper is built into the heat exchanger component. In this particular system network, there is a heating coil to provide backup source of reheat if/when the heat exchanger is insufficient to reheat the supply air to the desired temperature after sub-cooling for dehumidification. There is also an explicitly modeled bypass damper for the supply side of the heat exchanger and duplicate supply fan component (think of this as a meter with a performance curve) on the path through the supply side of the heat exchanger to account for the added pressure, and thus added fan power required, to move air through the heat exchanger when this component is not bypassed. I’m not sure whether this can be done in E+, but this ApacheHVAC example may give you some ideas:

[cid:image001.jpg at 01CF799C.D8F3F740]

Cheers,
Timothy

[IES]<http://www.iesve.com/>

Timothy Moore
Senior Product Manager


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From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Keith Swartz
Sent: Tuesday, May 27, 2014 8:29 AM
To: Aaron Boranian; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Air mixer for fresh air loop in E+?

Aaron,

I don’t know enough about EnergyPlus to know if it can model the system you described, but the main programs that I use, Trane TRACE and eQUEST, cannot. I have dealt with it in the past by using the manufacturer’s software to model the DOAS, removing the ventilation from the main model, then combining the results in a spreadsheet. The spreadsheet for the SEMCO Pinnacle (which sounds similar to what you have) is available at http://www.semcohvac.com/index.php?page_id=94&pl_category=9. The spreadsheet does not directly output the energy numbers that I needed, but I was able to get them indirectly by manipulating the utility costs. For example, to get kWh I entered $1/kWh for the kWh cost and $0 for the other utility costs so that the cost output equaled the kWh that I needed.

For a project that had a more complex DOAS, I had to create a custom spreadsheet to model it using basic psychrometrics. You might be able to access the presentation I did at last year’s ASHRAE Energy Modeling Conference at https://www.ashrae.org/membership--conferences/conferences/ashrae-conferences/emc2012. I was told afterwards by someone from IES VE that their software could model the system I had, so that may be worth looking into if EnergyPlus won’t do it for you.

Sincerely,
Keith Swartz, PE, BEMP, LEED AP
Senior Energy Engineer | Energy Center of Wisconsin | Madison.Chicago.Minneapolis
608.210.7123 | www.ecw.org<http://www.ecw.org/>

From: Aaron Boranian [mailto:flyn.hawyn at gmail.com]
Sent: Friday, May 23, 2014 12:45 AM
To: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] Air mixer for fresh air loop in E+?

Hey all,

I am trying to model a heat exchanger assisted cooling coil for the fresh air system of a laboratory building in Singapore.  Essentially, outdoor air (32C DB/ 26C WB) passes through the supply side of the heat exchanger (24C DB/ 24C WB), then passes through the cooling coil (13C DB/ 13C WB).  Outlet air from the cooling coil then passes through the secondary side of the heat exchanger (28C DB/ 18C WB).  In order to attain constant supply air DB temperature of 22C, design has allowed for mixing of outlet air from the cooling coil with outlet air from the secondary side of the heat exchanger.  Is it possible to model this in E+?  Somehow "trick" it with the OA mixer component?

Regards,
--
Aaron Boranian
Research Associate, Energy Research Institute @ Nanyang Technological University (ERI at N)
M.S. Civil Engineering, Building Systems Program, University of Colorado at Boulder
B.S. Engineering - Civil Specialty, Colorado School of Mines
Cell: (+65) 8588-5961
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