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Old 03-07-14, 09:54 PM   #21
buffalobillpatrick
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where2, I wrote you back a detailed PM but it was discarded when I sent it as I have too few posts. Drat!

Mikesolar, yes I have drooled reading about Viessmann boilers. I have installed HTP, Triangle tube Solo 60 that's in my current house, & Weil-McLain for buddy.

NiHoeMike, thanks for info

This is sourced from the solar tank.

"From 80* down to 35* I plan to source this to the heatpump evaporator. The destination from the condenser is the 120 gallon DHW / buffer tank."

I want to keep the 120 gallon DHW / buffer tank in the 120-145* range.

So it sounds like I need a R410a compressor?

Surplus City has this one:

2-1/2 TON AC/HP SCROLL COMPRESSOR, VOLT:208/230, HERTZ:60, PHASE:1, LRA:96.7, CAPACITOR:45 X 370(NOT INCLUDED), REFRIGERANT:R-410A, CONNECTION SIZE:1/2" X 3/4" SWEAT, HEIGHT:16", BASE DIMS:7-1/2" X 7-1/2", WEIGHT:68 LBS, ORIGIN:USA

SCL # : 171294

MFG : DANFOSS

MFG # : HRH031U1LP6

would this be a good choice & is the voltage correct for 240VAC ?

BBP

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Old 03-07-14, 10:48 PM   #22
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Quote:
Originally Posted by buffalobillpatrick View Post
This is sourced from the solar tank.

"From 80* down to 35* I plan to source this to the heatpump evaporator. The destination from the condenser is the 120 gallon DHW / buffer tank."

I want to keep the 120 gallon DHW / buffer tank in the 120-145* range.

So it sounds like I need a R410a compressor?
You'll probably be better off with two separate heat pumps and two storage tanks, one for the central heating/hot water first stage and one for the hot water second stage. The first one operates with a water temperature of 80-100F, so a R22 compressor would be just fine. The second one needs a R410a compressor as the condensing temperature can be very high, but much smaller. Keep in mind that the GE Geospring uses a refrigerator compressor, so you don't need very much, especially when you have the big one doing most of the work in cold weather. A 5000BTU/hr compressor (like one in a cheap window A/C) would likely be more than sufficient.

Exactly what temperature do you want for the first buffer tank? You said that when the solar tank is 80F or more, you want to bypass the heat pump entirely. Therefore, I used that to imply that you wanted 80F as a minimum. The second buffer tank (can be much smaller, as in 40 gallons or less, whatever size turns out to be most common and cheap) is what brings it all up to the temperature you set for DHW. Note that washing dishes is about the only thing that needs 140F water, so you'll get great efficiency gains by using a lower temperature (say 110F) for other uses and a digital control system to select the temperature. (I suggest something like the Raspberry Pi as it's cheap but easy to network.)
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Old 03-08-14, 12:23 AM   #23
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NiHaoMike, thanks again, I will try to make it clear.

The 120 gal DHW / Buffer tank is a Thermal accumulator, it will recieve heat from either the boiler or solar via this new heat pump. It has HX
to seperate the nasty boiler / radiant water from the potable DHW.

Heat can flow through this HX in either direction as required. The boiler will have long Eff. burn times. The zones can sip heat out as required without firing the boiler. The boilers only customer is the aqustat on this tank.

The 1,000 gal solar storage tank will be burried outside the basement.
It's temp. will vary quite a bit, possibly from 180* when there has been good sun & weather down to 35*

It will have a 300' loop of 1" pex in the top that will preheat the well water coming into the 120 gal DHW / buffer tank on any DHW draw. well water is just over 40*

There is also a 2nd HX loop in the top of the solar tank of O2 barrier 3/4" pex that will provide heat directly to the radiant floor system, via a Taco ODR controlled TMV which provides appropriate temp. water to a Grundfos Alpha pump to whatever zone of the hydronic floor that needs heat. I will use this source of heat whenever the solar tank is above 80*

When the 1,000 gal solar tank is below 80* and above 35* AND the aqustat on the 120 gal tank is calling for heat, instead of firing the boiler, this new WtW heat pump will heat the 120 gal DHW / buffer tank.

"From 80* down to 35* I plan to source this to the heatpump evaporator. The destination from the condenser is the 120 gallon DHW / buffer tank."

"I want to keep the 120 gallon DHW / buffer tank in the 120-145* range."

I only want to build 1 WtW heat pump if at all possible, as I have already bought all the rest of this equipment.

BBP
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Old 03-08-14, 08:32 AM   #24
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Then you'll certainly want a R410a compressor. Oversize the condenser and evaporator as that will get you better efficiency and allow it to more easily deal with high evaporating temperatures. Then add in a high pressure cutout (set for about 350-400 PSI), a low pressure cutout (set for about 50 PSI), and a delay on break timer (5 minutes or more, preferably 15 minutes or so). Use an oversized liquid line filter drier with the outlet facing down, as that will be your liquid line receiver. The TXV should be R22 and matched to the compressor, internal or external equalization depends on how restrictive the evaporator is. (A "snake" probably isn't restrictive enough to use external equalization unless it has multiple loops and a distributor.)

The thermal inertia of your system is so high that you probably won't see much real advantage of using a VFD. Use a "minimum time" method of control, where the controller turns on the compressor and pumps and leaves it on for a minimum of say 20 minutes (unless manually switched off or tripped on a fault), then turn it off when the required variable is met. Then it waits say another 20 minutes before it lets it come on again. (The latter is a delay on break but most delay on break modules won't let you set them that high.)
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Old 03-08-14, 08:44 AM   #25
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I don't know enough about heat pumps to know what they are capible of, or what is reasonable for Eff.

Could I input solar tank water in the entire range of 35* up to 180*
and
output water that is very hot, say 200* down to 150* ?

BBP
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Old 03-08-14, 09:09 AM   #26
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150F or so is already getting close to the limit for a R410a compressor running on R290. The evaporating temperature can go to maybe 100F, higher if you use a VFD. Counterintuitively, lower evaporating temperatures are more problematic with high condensing temperatures due to higher compression ratios. You might want to add a thermal sensor to the discharge line. 200F is the maximum limit for most applications, with 180F or so being the preferred maximum.

Solid state heat pumps can go all the way to the boiling point and beyond, but they're nowhere as efficient as compressor heat pumps.
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Old 03-08-14, 10:18 AM   #27
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150* output would work, just would take longer to heat the Thermal Accumulator.

"The evaporating temperature can go to maybe 100F, higher if you use a VFD."
As in getting a 3-phase compressor + VFD ?

"You might want to add a thermal sensor to the discharge line. 200F is the maximum limit for most applications, with 180F or so being the preferred maximum."
This would turn off compressor to protect it ?

Is the 20 min on/off cycle to allow the compressor to cool off ?

BBP

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Old 03-08-14, 10:46 AM   #28
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I just bought on Ebay: New GEA flat plate HX ref./water, 40 Bar, 9 Ton. Use this for condenser?

A few days ago I bought on Ebay: New GEA flat plate HX ref./water, 30 Bar, 4.7 Ton. Use this for evaporator?

On the TXV selection, I dont know either HX restriction to flow on the ref. side, I would guess low, the water side is plenty big.

The high pressure cutout would go on the compressor output & the low pressure cutout on its input?

Do you think I should get flare or sweat for the wet line filter/dryer & TXV ?

BBP

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Old 03-08-14, 10:49 AM   #29
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Single (split) phase VFDs do exist, but 3 phase VFDs are more common and cheaper on the surplus market. If you go that route, get a VFD with a RS232 or RS485 control and an interlock loop for easier control. Connect the RS232 or RS485 to a Raspberry Pi or similar using a USB serial adapter, onboard UART (plus level shifters) or equivalent. The interlock loop is for the high and low pressure controls. (The delay on break is no longer needed since the VFD would act as a soft start.) Put the VFD within a few feet (shorter is better) of the compressor to avoid standing wave issues.

The 20 minute on/off cycle is just to prevent short cycling. It tries to keep the compressor running for at least 20 minutes at a time (only exception being a fault trip or manual command) and also preventit from restarting until at least 20 minutes have passed. That's just an example - you might want to try different times.

Once the discharge temperature gets near the limit, the only thing you can do is lower the condensing temperature. In practice, R290 is very good with keeping discharge temperatures low so I wouldn't expect problems.
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Old 03-08-14, 01:18 PM   #30
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Quote:
Originally Posted by buffalobillpatrick View Post
I don't know enough about heat pumps to know what they are capible of, or what is reasonable for Eff.

Could I input solar tank water in the entire range of 35* up to 180*
and
output water that is very hot, say 200* down to 150* ?

BBP
The usual input temperature limit for a GSHP is 20C/68F The one I have only allows 15C maximum. The problem is that the compressor can overheat, it needs the cool water input to keep it cooled.

I mix the return water from the heat pump with the water from the seasonal store in a small 100 litre buffer tank. I suppose in time there will be heat pumps made specially to be used with warmer inputs.

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