Hello All,
I had a couple questions that I was hoping someone could clear up for me.
1) Boiler and Cooling Tower Set points: The boiler set point states
its range from 32 ?F ? 100 ?F. But the program will not run if the set point
is over 65 ?F. Has anybody encountered this before? Is this normal or
should I be able to have a higher value? For the cooling tower, is there a
place where I can input the set points?
2) Max Heating COP: In the building tree under the Zone Level and in
the Mechanical Tab I can set the heating COP. It says in the EE4 Help Guide
that I should be able to set this value as high as 10. But the program will
not let me input anything higher than 8. Again, is this normal and has
anyone else experienced this? I am trying to model a hybrid heat pump;
therefore I would like to input the highest COP possible.
Please let me know if anyone can shed some light on the issues I?ve
expressed above. Thank you in advance.
Cheers,
Justin Elkin
2) Yup - 8 is as high as you can go.
1) The boiler setpoint (for a heat pump condenser loop) must be lower than the cooling tower setpoint which is set on the cooling tower tab.
Brian Fountain
bfountain at greensim.com
What software are you using, Justin? I have seen EnergyPro require the
cooling tower minimum water temperature to be above the boiler
setpoint. This might be correct for a water source heat pump system,
but I don't think it is correct for a hot water reheat system, for
instance. I have never been able to get EnergySoft to tell me why this
limitation exists.
You may have a different situation, but I have seen that error in EnergyPro.
Robert Wichert P.Eng. LEED AP BD&C
Justin,
You can modify the HEATING-EIR (reciprocal of COP) in the DOE code for all zones to achieve the high COP's of a hybrid heat pump (so that you aren't using electricity (compressors) energy for heating).
Kind regards,
Danielle Krauel P.Eng., LEED AP
Justin,
Do you have any ideas on how to get around having the cooling tower
setpoint above the boiler setpoint? This makes no sense to me with a
cooling tower cooled condenser and a boiler heated reheat loop. They
aren't even connected!
I agree that the limitation is proper for a heat pump, since you don't
want the boiler just rejecting heat to the cooling tower, but if the two
loops are not connected (like a hydronic heating system with a water
cooled condenser DX system) the limitation doesn't make sense.
Robert Wichert P.Eng. LEED AP BD&C
Hi Robert,
What I heard is the DOE2.1 gets unstable and will crash if you have a high temperature setpoint. EnergyPro and EE4 are both DOE2.1 based. That why this limitation exists.
Also, I believe that the boiler and the cooling tower (in EE4) are on the same loop, and your boiler set point should be set lower than the cooling tower's.
Hayssam Barhoun PEng, LEED AP, PhD, BEMP
Thank you Robert and everyone else for your replies.
Robert, The program that I am using is EE4 and it does seem that the boiler
set point must be below the cooling tower set point.
Justin Elkin
Yes, Hayssam, I have been told the same thing, that the boiler and the
cooling tower are in the same loop in DOE 2.1. I don't know enough of
the code, but whoever wrote it had never heard of hot water reheat with
a water cooled condenser!
It seems like for that part of DOE 2.1, they only considered water
source heat pumps and ignored VAV reheat systems. Or maybe they figured
that all systems with hot water reheat would be air cooled condensers,
but that isn't true.
Robert Wichert P.Eng. LEED AP BD&C