Re: [TRNSYS-users] Heating Coil: Type 670-1 bug

[David Bradley <bradley@tess-inc.com>]

Fred,
 Heating coils are pretty easy because you don't have to worry about condensation. With cooling coils, if memory serves, you can't quite use the same effectiveness concept because there is both sensible and latent cooling going on. Typically what you have to do is to adjust the bypass fraction at the coil's rated conditions in order to tune the model to a particular coil's performance. The bypass fraction method essentially assumes that some of the air comes out of the coil saturated at the coil water temperature and some of the air bypasses the coil entirely and remixes downstream.
Best,
 David

Fred Betz wrote:

Sorry David, my wording was very poor.

 

What I was trying to get at is that the approach temperatures appear too small.

 

I have 22C air entering the coil and 29C air leaving the coil.

 

I have 32C water entering the coil and 25C water leaving the coil.

 

That is a delta T of just 3C, or 5.4F between the air entering and the water leaving.

 

It should be about 7-10F based on project experience.

 

This might be splitting hairs, but with 500,000 CFM of air flow, 1 degree means thousands of dollars. Therefore, every item gets scrutinized.

 

Also, I was hoping there was a way to set the effectiveness on the cooling coil like I was able to on the heating coil.

 

Thanks,

 

Fred

 

 

Fred Betz  PhD., LEED AP Sustainable Systems Analyst

AEI | AFFILIATED ENGINEERS, INC.   5802 Research Park Blvd. | Madison, WI  53719 P: 608.236.1175 | F: 608.238.2614   fbetz@aeieng.com  |  www.aeieng.com

 

 

From: David Bradley [mailto:bradley@tess-inc.com]
Sent: Monday, March 29, 2010 4:18 PM
To: Fred Betz
Cc: trnsys-users@cae.wisc.edu
Subject: Re: [TRNSYS-users] Heating Coil: Type 670-1 bug

 

Fred,
 I think you might be confusing efficiency and effectiveness. Effectiveness is actual energy transfer divided by maximum theoretically possible energy transfer. The air and water side heat transfers need to be equal or else there is an energy imbalance across the coil.
Best,
 David
 

Fred Betz wrote:

All,

 

There appears to be a bug in the Type 670-1 heating coil.

 

I set the effectiveness of the coil to 0.70, but the air and water side heat transfer rates are approximately equal.

 

Anyone have a fix?

 

Fred

 

 

Fred Betz  PhD., LEED AP Sustainable Systems Analyst

AEI | AFFILIATED ENGINEERS, INC.   5802 Research Park Blvd. | Madison, WI  53719 P: 608.236.1175 | F: 608.238.2614   fbetz@aeieng.com  |  www.aeieng.com

 

 

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Thermal Energy System Specialists (TESS), LLC 

David BRADLEY                      22 N. Carroll Street - Suite 370 

Partner                            Madison, WI 53703 

                                   USA

P: +1.608.274.2577 

F: +1.608.278.1475

E-mail: bradley@tess-inc.com 

Web Pages:  http://www.tess-inc.com    and      http://www.trnsys.com

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-- 
***********************************************************************
Thermal Energy System Specialists (TESS), LLC 
David BRADLEY                      22 N. Carroll Street - Suite 370 
Partner                            Madison, WI 53703 
                                   USA
P: +1.608.274.2577 
F: +1.608.278.1475
E-mail: bradley@tess-inc.com 
Web Pages:  http://www.tess-inc.com    and      http://www.trnsys.com

***********************************************************************