geothermal unit with variable speed compressor?
I plan to install a geothermal in Northeast PA. Primarily heating, maybe 10% cooling. I'd been planning on a 5 ton single stage Waterfurnace unit.
I've just looked at the new Copeland variable speed compressor:
I looked at the waterfurnace and fhp web sites. Neither has a unit with a variable speed compressor - just the two stage scroll.
Does anyone have a geothermal unit with a variable speed compressor?
Yes WaterFurnace does have a unit with a VFD(variable frequency drive) compressor... it won't be out until August of this year though. It is supposedly going to be called the WaterFurnace Series 7, the envision unit has changed to the WaterFurnace Series 5 and the Legend line will become the WaterFurnace Series 3. The WaterFurnace dealer convention is coming up April 16-18th and I am heading to Orlando to check it out and then we should all have more information on the units. Also you might want to subscribe to my YouTube because as soon as we put one in, we will have a video of it.
Not to derail this topic too much, but I'm curious about this compressor. Do you know if it'll have some strategy for start-up to reduce amp draw? If it does, I'm wondering what minimum wattage generator would be needed to run one of these.
From the limited info I've gathered, water source vs. air source heat pump compressor sonly differ in the type and size of condenser coil used. THe compressor doesn't know any better. In both cases, its' refrigerant vapor is flowing in copper tubes, the cooling medium that sourrnds those tubes is not terribly relevant to the comrpessor as long as enough heat is transferred to maintain the proper pressure ranges.
It's mostly a marketing and spply demand thing. On the water source side, it's more diminishing returns I believe. Going from a equivalent of 26SEER to lets say 32SEER, isn't as dramatic as going from 18SEER to 23SEER as you do on the air source units. So the ROI isn't as good.
As for start-up wattage.. good question. Any VFD unit will draw far less peak amps than a straightline starter. At minimum it will still be nearly 2X max running load. The inrush current time period will simply be longer. The same net energy is spin-up the compressor either way, it's just spread-out over a longer time frame on a VFD.
WaterFurnace and I think some other geo units have soft starts with optional accessories.
Originally Posted by crash11
A WF 3 ton two stage unit without intellistart takes 82 amps to start, with intellistart it only takes 29
A WF 5 ton two stage unit without intellistart takes 118 LRA to start and with intellistart only 41 amps.
There are some downsides to a VFD on a ground source. If you know how a desuperheater works, it is because it takes the excess heat from the compressor and puts it into water to preheat it. If a compressor is always running perfectly there is little to no desuperheater function.
Originally Posted by motoguy128
But WF expects COP's to be above 6 and below 7, no idea on the EER's
VFD compressor has benefits but disadvantages as well. Here a few:
+ superior water temperature control
+ increased part load efficiency
+ soft start
+ reduced compressor cycling
+ reduced water system sizeing
- higher first time costs
- electrical losses (heat) of the vfd (if its not refrigerant cooled) especially on full load
- more expensive spare parts
But for the overall efficiency of the system (and this is what counts) the ground source pump and distribution efficiency is also quite important. Generally: When you expect extended part load operation VFD is the best choice.
"Quality exists, when the price is long forgotten."
I have BIG questions about the use of VFDs and the digital scrolls on any system that is heating water especially if there is a big buffer tank (120gal) like the ones we use. I think it has a place on air to air units and maybe water to air.
I've only seen vfd compressors on water to air (Mitsubishi and McQuay), but good capacity control and load following would seem to reduce the need for or size of a buffer tank on a water to water system. Also soft start benefits are important as geothermal has a lot of synergy with off the grid or nearly off the grid projects. Keeping the capacity of generators and solar/battery inverters smaller is important for project cost.
With my HVAC/R company, we install WFI GHP and Carrier A/A heat pumps. It's reputed that WFI will be using Danfos compressors....anyone heard a Danfos scroll??? They definitely won't fly in house. The Carrier 3 ton particularly has a definite loud 'buzz' to it at low ambient (-3 degC and lower) so it's going to be a problem on closed loops that can run sub zero). The Carrier uses the Copeland variable and it is very, very low LRA....ie in a 21 FLA they have somewhere in the range of a 29 LRA!!!!
The Carriers are also needing some more work on their defrost algorithm as they are icing on bottom circuits from very cold (and heavy) latent liquid not moving out of the coil and allowing for 'hot gas' to de-ice them.
The do provide hotter air and lower air volumes and with the huge size of the coils I've seen 0 deg approach on an inside coil with a sub 50% speed running and they turn up to 7000 rpm....
"The quality you deserve is not expensive---it's priceless"
I have a WF 6 ton W/W with 2 Danfoss scrolls on a building I look after. I haven't had to service them yet as they are only 2 years old and working OK.
The variable speed compressor heatpump that WF had at the dealer meeting last year (2011) was very quiet. It was sitting out in the open in a hallway. They would vary the compressor speed up and down and you could hardly tell that the unit was operating. I think that it was a three ton model.
I was told this past weekend that the Danfoss plant here in AR is gearing up production of their VS compressor (for WFI?).
For the general market, I am waiting for it as well.
Originally Posted by Bill Lee