Nothing to worry about. It is proper to run a water coil at 12.5°C. Why wanting to run a large DX coil at the same low temperature?
I do not think many people will run a 40kW DX coil as a single unit in the VAV mode without the VRV or modular compressor mode.. Watch the design cooling temperature at the Sizing:zone object as well. It was 16°C, now it is 14°C. I have seen people lowring it to 12.7°C.
With a system that the compressor pump never turn off and the fan never turn off, and a user who do not have the tool to asign the correct values in the fields for variable speed what do you expect. That is why autosizing and a slightly higher design temperature eliminated most of the warnings.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: eglyon@xxxxxxx
Date: Tue, 20 Mar 2012 19:28:31 +0000
Subject: RE: [EnergyPlus_Support] frost/freeze error
It appears that the Energy+ DX model does not include simulation of what is commonly called a low ambient control for a DX cooling system. Basically the low
ambient control monitors the system operation and turns off the condenser fan if the outdoor air conditions push the system too far. The DX system continues to operate with the condenser fan either off or cycling on and off. This could be programmed with
the EMS as a capacity reduction for the condenser coil, but I am not sure how to do this or if it can be done with the current DX cooling model.
Ned Lyon, P.E. (MA)
Staff Consultant
SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
781.907.9009 fax
www.sgh.com
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
On Behalf Of CleanTech Analytics
Sent: Tuesday, March 20, 2012 3:11 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] frost/freeze error
Richard, thank you kindly.
Your explanations where very clear and useful..
A part of the problem was that I had used an HVAC system sized for one climate, and had moved it from one location to another, so the system was incorrectly sized...
Jeremiah D. Crossett
CleanTech Analytics
503-688-8951
This document may contain valuable information proprietary to CleanTech Analytics which is private and confidential. It may not be shared, copied, stored or transmitted in any form without the prior written consent of CleanTech Analytics
On Tue, Mar 20, 2012 at 6:14 AM, Jim Dirkes <jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
Dear Jeremiah,
Your DX coil is trying to operate in cool weather. When it does, it applies its full capacity to the airstream and cools it down to freezing temperature.
This is the same error that Joe Huang posted about the other day (I think).
You?ll need to :
1. Ignore it (after confirming that it?s not indicating some other problem)2. Turn off the coil during cold weather (after looking at the weather file to see when weather is below about 55-60F)
3. Run an EMS script to turn off the coil whenever outdoor temp is lower than a set value
p.s., Certain ?baseline? systems (e.g., a heat pump serving an interior zone) don?t handle the situation well where an economizer is not used such as is the case in a warm climate zone. They need cooling in the cold weather, but the DX system doesn?t like operation then. (This is not a likely ?real? system, since engineers know these things. But a ?baseline? is not real?)
Here?s an EMS routine (grateful credit for which goes to Jean Marais and somebody at the Help desk a few months back):
DX coils that you want OFF via this routine must have their Unitary object specified with the same schedule which the EMS routine is turning on and off (?SchCpct_LowTempOFF? in this example)
The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From:
EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx]
On Behalf Of CleanTech Analytics
Sent: Monday, March 19, 2012 11:34 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] frost/freeze error
Dear List,
Any advise on how to approach this error?
Thanks
************* ===== Recurring Error Summary =====
************* The following recurring error messages occurred.
*************
************* ** Warning ** Coil:Cooling:DX:SingleSpeed "BLOCK1:ZONE1 AHU COOLING COIL" - Full load outlet temperature indicates a possibility of frost/freeze error continues. Outlet air temperature statistics follow:
************* ** ~~~ ** This error occurred 3849 total times;
************* ** ~~~ ** during Warmup 0 times;
************* ** ~~~ ** during Sizing 0 times.
************* ** ~~~ ** Max=1.999729 Min=0.701477
*************
Jeremiah D. Crossett
CleanTech Analytics
This document may contain valuable information proprietary to CleanTech Analytics which is private and confidential. It may not be shared, copied, stored or transmitted in any form without the prior written consent of CleanTech Analytics
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