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Modeling Indirect-Evaporative Cooling with Winter Heat Recovery

asked 2014-09-18 16:30:39 -0500

updated 2014-09-30 09:42:41 -0500

Specifically, do you use two components- a direct evaporative cooler (spray chamber) on the exhaust side and a heat exchanger, and if so, what efficiencies do you typically use? I am seeing one whole-system rating from manufacturers: about 70% (in the Bay area). If winter heat recovery has a lower effectiveness than the IEC rating, how do you set-up/control it? I am specifically using IES<ve>, but any general information would be useful, or how other softwares handle this system.

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answered 2014-09-19 00:35:59 -0500

Joe Huang gravatar image

updated 2014-09-19 00:59:31 -0500

It sounds like you're working with a single-stage indirect evaporative cooler that doubles as a dry heat exchanger for heat recovery in the winter. In that case, you should just model it as a single component with a certain effectiveness, which is the fraction of the total wet-bulb depression (Tdry - Twet). Most of the literature I've seen have default effectivenesses (?) of 0.85 for direct and 0.60 for indirect evap coolers. If you want to get a little more fancy, you could add an effectiveness curve that varies with the part-load ratio and wet bulb temperature. Back in the early 1990's, I worked with a Visiting Scholar from China (Prof. Chen Peilin) who developed a detailed indirect evaporative cooler model that he then used to calculate effectiveness curves for IEC precoolers that I then incorporated into the DOE-2 program see this paper. I'm sorry that I don't have digital copies of most of my evap cooling papers, but I do have the last one where I calibrated my models against PGE measured data here that might be of help.

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Thank you! I also found this page on from Big Ladder that helps with a lot of my questions:

Anna Osborne Brannon gravatar imageAnna Osborne Brannon ( 2014-09-22 16:03:55 -0500 )edit

answered 2014-11-24 14:59:26 -0500

updated 2014-11-24 15:07:31 -0500

I've modeled this before using OpenStudio. OpenStudio 1.5 or later offers a lot of flexibility by allowing direct or indirect evaporative coolers to be placed on the outdoor air exhaust/supply nodes. One option would be to place an indirect evaporative cooler on the supply node along with a HX coupling the exhaust and supply air streams. Another option would be to place the direct evaporative cooler on the exhaust stream with a sensible HX.

If you want to model a direct/indirect evaporative cooling system you could place a direct evaporative cooler on both air streams and couple the streams with a sensible HX. There is a measure that automates this available through the BCL.

For the indirect/direct evaporative cooling objects you can specify sensible and latent effectiveness's respectively. For the air to air HX you can specify both a sensible and latent effectiveness at various airflow rates for heating and cooling.

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@Lincoln, when modeling this system did you place a separate setpoint manager for the direct evap cooler on the exhaust stream? If so which one? I am just wondering if EnergyPlus will operate the evap cooler in the exhaust steam correctly without more input from the user.

TaylorRoberts gravatar imageTaylorRoberts ( 2016-04-11 17:27:21 -0500 )edit

yes, put a setpoint manager on the outlet node of the direct cooler. The direct evap cooler in E+ has a field to input the Sensor Node Name. I think OpenStudio fills this input in for you but I would double check...

Controlling the direct cooler in different conditions may be difficult so you could also look at using an indirect cooler on the outdoor air inlet stream.

Lincoln gravatar imageLincoln ( 2016-04-13 10:53:20 -0500 )edit

answered 2014-11-24 14:32:59 -0500

crduggin gravatar image

I have modeled indirect evaporative cooling in the VE before. My system had two stages of evaporative cooling on the exhaust side that then runs through a heat exchanger. I ended up having to model the evaporative cooling with cooling coils rather than the spray chamber component. The possible controlled variables for the spray chamber were too limited. I controlled the cooling coils via heat transfer using the value from the manufacturers materials for each stage. I used an 80% sensible effectiveness for the heat exchanger. The cooling coil controls staged on and off based on the supply side leaving DBT off the heat exchanger. I hope this helps even though it's a bit late.

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Asked: 2014-09-18 16:30:39 -0500

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Last updated: Nov 24 '14