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natalie_p
03-13-2009, 03:41 PM
Hi all,
I am working on my first Heat Pump program Constant Air Volume with Defrost Controls. This is a commercial unit. Can you guys give me some information about the defrost controls?
We do not have control the the water pump, we control the condensing valve(s) and reversing valve. Another question I have is when the pump start and stop? How that pump is controlled? I understand that waterflow switch has to make before compressors are started.
Please give me some some information.
Thanks
Natalie
ddcfreek
03-13-2009, 04:09 PM
The pump should start with a demand for heating or cooling with a time off delay of maybe five minutes. As for your other question regarding defrost, why would you need it for a water source heat pump?

What are you programming?
natalie_p
03-13-2009, 04:22 PM
The pump should start with a demand for heating or cooling with a time off delay of maybe five minutes. As for your other question regarding defrost, why would you need it for a water source heat pump?

What are you programming?

Hi there,
Thanks for your respond.
I think I used the wrong word for it. I shouldn't call that "defrost".
All I want to do is the write a program to protect the outside brace plate from freezing during unoccupied mode when outside temperature gets too cold.
This is my first heatpump application but it is not the company first heatpump. The company sold a heatpump unit before without freeze protection. The outdoor brace plate was frozen during a cold night, it cost all kind of problems within the unit and it cost so much money for the company to fix the problems.
So how to write a program to protect the outdoor coil from freezing during unoccupied time if the outside temperature gets too low?
Thanks
ddcfreek
03-13-2009, 04:40 PM
Are you monitoring the water loop temp? If you are you could run the pump on a time-based schedule by outdoor air temp. The colder it gets the longer the pump runs and the shorter it is off. Then if the loop gets below a setpoint you can either just run the pump or start the compressor too. If you are not monitoring the loop then you are better off just running the pump 24/7 when the outdoor temp is below 40.

Is the outdoor coil a ground loop?
natalie_p
03-13-2009, 04:50 PM
Are you monitoring the water loop temp? If you are you could run the pump on a time-based schedule by outdoor air temp. The colder it gets the longer the pump runs and the shorter it is off. Then if the loop gets below a setpoint you can either just run the pump or start the compressor too. If you are not monitoring the loop then you are better off just running the pump 24/7 when the outdoor temp is below 40.

Is the outdoor coil a ground loop?
We control the controls the condensing valve base on the Condensing ReturnTemp and we monitor the Condensing Supply Temp. We DO NOT have control of the pump and we don't know how they are schedule that pump to run. All we get is the water flow swithes for both supply and return pipes. This is Rooftop unit and the outdoor coil is also attached to the side of the unit and will be on the roof as well.
As sum the pump runs 24/7, what do I need to do to prevent the outdoor coil from freezing up? Open the condensor valves? And/Or run unit in cooling mode???
theoldman
03-13-2009, 06:03 PM
Somebody shoot me!
amigo
03-13-2009, 06:16 PM
Somebody shoot me!

:D:D , I think it is time for a couple shots of glycol, bottoms up:eek: