[Equest-users] VAV with Electric Reheat

[Omar Katanani]

Dear all,

 

I had this discussion below a long time ago!

 

Basically I have a VAV system with Electric Reheat coils at the terminal
units to compensate for excessive cooling. Therefore, the reheat coils
are going to operate during the cooling season only.

 

Otto's advice below worked perfectly, until I decided to change the
Preheat leaving temperature from 70F to 69F (Air-Side HVAC --> Heating
--> Preheat --> Preheat Leaving Temperature) .The space heating
consumption due to diesel decreased by around 15%!

 

All I know is that the air is supplied to the zone at 54F. I would like
to see that the main proportion of heating is due to the hot water loop,
and a small proportion is due to the reheat coils.

 

Also, I do not have a conventional preheat configuration in the sense
that air is being pre-heated before going to the hot water coil. 

 

I would like to know the exact way to model a reheat coil system for the
scenario above. I attach my file for the Preheat leaving temperature =
69F. You can change it to 70F and see the difference in Diesel Space
Heating consumption!

 

Many thanks for your help in advance!

Omar

___________________________

Omar Katanani
Sustainable Design Engineer

Email: omar at ecoconsulting.net

 

EcoConsulting (Lebanon)

Nahas Building, 4th floor

4 St-Maron Street / Georges Haddad Avenue

Postal Code: 2028 5806 SAIFI

Beirut, Lebanon

Tel:          +961 (0) 1 971 266
Mobile:    +961 (0) 3 045 045

 

EcoConsulting (UK) Ltd
28 Marshalsea Road
London, SE1 1HF
Tel:  +44 (0) 207 939 0989
Fax:  +44 (0) 207 939 0981

Website: www.ecoconsulting.net <http://www.ecoconsulting.net/> 

 

  

________________________________

From: Otto Schwieterman [mailto:oschwieterman at fhai.com] 
Sent: 23 July 2010 20:22
To: Omar Katanani; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] VAV with Electric Reheat

 

Omar,

 

I have provided screen shots of air handler 1. I made the following
modifications and it appeared to run correctly.

 

 

 

 

 

 

 

Good luck, 

 

Otto

 

From: Omar Katanani [mailto:omar at ecoconsulting.net] 
Sent: Friday, July 23, 2010 12:48 PM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] VAV with Electric Reheat

 

Otto, it didn't work!

 

Dear all,

 

I discovered that the parameter "Hot Deck Max Leaving Temp" is necessary
in order to activate the main heating coil! If left to default, only the
reheat coils will operate.

 

Back to my case, where I had electric reheat. When I didn't specify the
"Hot Deck Max Leaving Temp", the hot water loop had zero flow because it
wasn't activated (and hence the error).

Now when I specified a value of 70F, I got rid of the error, but the
whole heating (99.9%) was electric, and a very small 0.1% was due to the
hot water loop.

 

A possible percentage of space heating sources is 80% hot water loop,
20% electric reheat coil. (or any other reasonable percentage).

 

I played a lot with the "reheat delta temp" and the "Hot Deck Max
Leaving Temp", the results slightly varied (change in the fuel
consumption of space heat, but still negligible compared to the electric
portion.

 

Any recommendations? I attach my files just in case...

 

Many thanks,

Omar

___________________________

Omar Katanani
Sustainable Design Engineer

Email: omar at ecoconsulting.net

 

EcoConsulting (Lebanon)

Nahas Building, 4th floor

4 St-Maron Street / Georges Haddad Avenue

Postal Code: 2028 5806 SAIFI

Beirut, Lebanon

Tel:          +961 (0) 1 971 255
Mobile:    +961 (0) 3 045 045

 

EcoConsulting (UK) Ltd
28 Marshalsea Road
London, SE1 1HF
Tel:  +44 (0) 207 939 0989
Fax:  +44 (0) 207 939 0981

Website: www.ecoconsulting.net <http://www.ecoconsulting.net/> 

 

 

-----Original Message-----
From: Otto Schwieterman [mailto:oschwieterman at fhai.com] 
Sent: 21 July 2010 17:56
To: Omar Katanani; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] VAV with Electric Reheat

 

Omar,

 

You can try using a pre-heat coil as your hot water coil in the air
handler and the electric heat in your re-heat coil.

 

 

 

 

 

 

 

 

 

From: Omar Katanani [mailto:omar at ecoconsulting.net] 
Sent: Wednesday, July 21, 2010 10:06 AM
To: Omar Katanani; equest-users at lists.onebuilding.org
Subject: [Equest-users] VAV with Electric Reheat

 

 

Dear all,

I'm sorry I've been nagging a lot lately, but believe me, you guys are
my only support!

I was using a VAV system, with the reheat source being the hot water
loop. I specified the Reheat delta temperature by trial and error to
25F. Everything is fine.

Now I got updated info from the client saying that the source of the
reheat is electric. I am getting an error message:

"Hot Water Loop  has zero design flow. Check input for consistency, or
specify design loads."

I read a couple of discussions. I understand that many factors will
affect this issue. The "Hot Deck Maximum Supply Temp", the "Reheat Delta
Temp", and the "Zone Entering Max Supply Temp".

I tried specifying the hot deck max supply temp to 70F, I got the
results attached in the pdf. However, the gas consumption part of the
space heating is negligible compared to the electric, while I thought
both will be of significant ratios!

My main question is how to get reasonable results, knowing that the main
heating source is the hot water loop, and the electric reheat is to fine
tune the temperature of zones experiencing different loads or so...

I know that the design temperature of the zones is 70F, and that the
temperature that is supplied to the zone should be 30 degrees higher
than the zone temperature (70+30=100F).

Any advice on how to choose the "reheat delta temp" and the "hot deck
maximum supply temp", or any other input parameter you feel that it
affects, is greatly appreciated.

Many thanks,
Omar
___________________________

Omar Katanani
Sustainable Design Engineer
Email: omar at ecoconsulting.net


EcoConsulting (Lebanon)
Nahas Building, 4th floor
4 St-Maron Street / Georges Haddad Avenue
Postal Code: 2028 5806 SAIFI
Beirut, Lebanon
Tel:       +961 (0) 1 971 255
Mobile:    +961 (0) 3 045 045


EcoConsulting (UK) Ltd
28 Marshalsea Road
London, SE1 1HF
Tel: +44 (0)207 939 0989
Fax: +44 (0)207 939 0981
Website: www.ecoconsulting.net

 
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