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Panasonic
Regular Guest
Hi,
I am converting an older GSHP from fixed speed to variable speed.
I am in the UK. The compressor being replaced is a Copeland ZH19K4E 240V-1PH-50Hz.
This is circa 7kW / 2Ton duty.
This is running on R407C. I am expecting to convert to R410A.
I am a refrigeration design engineer and will size up a new compressor correctly.
Currently looking at:
Danfoss
Copeland
Ideas of other manufacturers to look at too please?
SDC/Educational/Membership Committee*
Member
Welcome to H-Talk!Originally Posted by GSHPP
http://www.hvacrinfo.com/compressors.htm
Professional Member
Get a small 3phase compressor and run it on a VFD the VFD is capable of converting a single phase to 3 phase. Here is a chart from Copeland with there minimum speeds for there compressors.
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Regular Guest
Thank you all for your input! Very helpful!
Off to do some more reading!
So looks like i need a 230v/3ph (UK) compressor to work with a 1ph - 3ph VFD.
Professional Member
Always wanted to make my own . Havent had the time. What will the compressor speed be ran off of? Suction temp? Suction pressure? Or something else.
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Regular Guest
Its something i am looking forward to getting built. My fixed speed is awfully inefficient.
It will reference water discharge temperature and modulate to maintain that set point.
Professional Member*/ARP Committee
That sounds like a horrible way to control it,
When you get down in the depths of winter you will severely limit capacity, and run to the max right after change over from seasons.
Regular Guest
How will it limit the capacity in winter?
What are you suggesting the compressor speed should reference to maintain the correct water temperature?
The water temperature set point will of course be weather compensated.
Professional Member*
How are you planing on operating with almost twice the operating pressure?
Professional Member
How do you plan to convert your control conditions into modulating the compressor to the correct level. Are you going to be designing some custom electronics to take in your sensor inputs and then modulate the compressor accordingly. Or is something available off the shelf?
Control feedback can be complex and unless you model your entire system to make sure it behaves ass you expect you may end up with some weird operation.
Professional Member
A easier idea would to install a digital scroll. All the controls are readily available.
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Professional Member
Looks like the smallest digital is a 3ton. Which will unload to 10% or 3600btu.
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Professional Member*/ARP Committee
Weather compensated wouldn’t work either.
Your assuming a constant inlet water temp and that water temp is directly based on outdoor temp.
So, let’s say you set your water temp at 25 degrees.
Incoming water temp is 45. It will run 100 percent.
Then as you progress into the season, your incoming water gets colder, say 27 degrees. Now your running 40 percent.
I’m assuming closed loop methanol.
Either way, your controlling your capacity based on your water temperature, not the space requirements, which is backwards.
Professional Member
407c to 410a? Unit designed for the higher pressures?
Regular Guest
I think we are talking about different applications of the heat pump.
This is a ground source heat pump - which in the UK produces hot water for heating floors / radiators. Not a split system with the condenser producing hot air.
So when i talk about referencing water temperature, i am talking about the hot water going out to the heating distribution side.
With a fixed speed compressor, the unit currently references the returning water temperature from the building. If you want 35 degC water for the floors, you assume a 5 degC average delta and set the return setpoint to 30 degC.
This is ineffective as at the start of the season with warm ground temperatures the compressor produces almost 30% more heat than at the end of the season.
This giving higher discharge water temperatures at the time when you want them to be reduced. If it had some basic compensation for the ground water return to reduce the setpoint maybe that would help, but regardless, the compressor is oversized at the start of the season, unable to reduce its capacity and short cycles until the depth of winter when the compressor design load better matches the distribution load.
I think your point about matching space requirements is now answered. I think you believed i would be matching load to ground water temperature which would be wrong.
Regular Guest
Very good question, easily overlooked i am sure! Thanks for commenting.
Simple answer yes.
This is a project, bit of fun for me while saving money on a new heat pump, i also hope to get the best efficiency for my property.
The heatpump currently has it HP cutout at 26 bar(g). For R410A that will increase to 39.5. The heat exchangers are rated for PS 50. Anything else i would upgrade as required.
I am not set on converting to R410A, but the inverter driven compressors i was looking at before posing here were all 410A.
All i am using from the old heat pump is the heat exchanges, frame, pumps. New compressor, control system, EEV, filter-drier, instrumentation as required.
Its a project.....
Professional Member*
by using 407C in a pump designed for 410A you'll loose about 30 + % capacity.
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Regular Guest
I concur with that statement.
Its not the plan here however. New compressor.
Professional Member*/ARP Committee
Oh. Your modulating based on LOAD side discharge, using an outdoor reset.
Ya, that’s a completely different animal!
That’ll work.
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