Dear all,
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 20F. 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".
First of all, is the sum of the first two equal to the third?
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 just to fine tune the temperature of zones experiencing different loads or so...
I played with all values but I can't figure out the pattern. 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" is greatly appreciated.
Many thanks,
Omar Katanani
?You have an electric heating system !! ?There IS no hot water flow !! Get rid
of the hot water loop !!
John Aulbach
John,
The primary heating coil in the air handler operates on the hot water loop.
It is just the terminal units that have an additional electric resistance coil that is used in the cooling season to raise the air temperature of the zone if the internal loads of the zone drop for some reason.
That's why I need the both the hot water loop and the electric resistance.
Best,
Omar Katanani
Dear all,
Hope you had a relaxing weekend!
Is there any way that I can enter the capacity of the electric reheat coils?
There is this input parameter called "Heating Capacity". I guess it is for the whole AHU, right?
The issue is that I'm not able to figure out how to model the VAV with electric reheat, as there are many temperatures that I'm asked for including "Reheat delta Temp", "Zone Entering Max Supply Temp", and "Hot Deck Max Leaving Temp".
If I left everything to default values, I get an error of "Hot Water Loop has Zero design flow.."
Many thanks,
Omar Katanani
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 Katanani
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.
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 Katanani
Omar,
I have a few comments. First of all, when I opened your file I got many
warnings stating that the windows were not positioned correctly. I am
using a modified eQUEST version of 3.63 supplied in a training from
Marlin Addison. You may not receive the warnings depending on what
version you are using. You may want to double check your window
placements.
I have provided screen shots of air handler 1. I made the following
modifications and it appeared to run correctly.
Also, I would recommend having an experienced modeler to review you
model when it is finished since this is your first one and there appears
to be many small items that could be improved.
Good luck,
Otto