ASHP question

[Xringer]

Here's a post from a guy in Shrewsbury, MA..

Sanyo mini split AC (inverter/variable speed) - Page 27

[Student 07]

Hi,
I have been looking at air source to water heat pumps as an alternative to a geothermal heat pump. I found the Mitsubishi Ecodan, but it isn't for sale in the U.S. I then found the Daiken Altherma, and got a qoute for it- $18,500. To me that is extremely expensive, payback would be exceptionally long.

Looking further I found heat pumps for swimming pools, Aquatherm for example. They cost between $2,000 and $3,000. Instead of heating a large pool couldn't they be connected to a small (120gl) tank inside the house similar to how a solar system is set up?

I know most of them are only set to operate at 90*, but with a small tank (compared to a swimming pool) wouldn't it get hotter? Or can they be set to a higher temp? Most of them also have a minimum flow rate of 30gpm, maybe a larger heat exchanger could get around this requirement?

I don't understand why the Daikens are so expensive. Maybe supply and demand is controlling the price. With high fuel prices any alternative is seen as an opportunity to make a fortune. Whew, had to vent.

Does anybody know if this would work, or why it wouldn't?

[Xringer]

My off-the-cuff guess is, there is a thermistor measuring the hotwater output connection,
and it might be an easy hack to trick it into pumping out hotter water.
But, it might still only be only a little hotter..
Check out the temperature at different pressures on this R410A gauge.
At 440 PSI, the gas is only up to 120 degs F.
That's about as hot as a Sanyo mini-split indoor coil gets..


What's the application for your hotwater? (and how many BTUh do you need?)

[Student 07]

Hi Xringer,
I have a Propane water heater that I use for space heating and DHW. It is rated at 58,000 BTUs. I really think it is oversized and I would be okay with 50,000 BTUs at the most (4 ton unit).

I know that the heat pump will have trouble when it gets really cold outside, the recovery time is slower, and it can't get the water hot enough for laundry, showers, dishwashing etc.,

What I am thinking is to use a heat pump/ solar to preheat water in a tank that is connected in series to my current water heater. If the water in the storage tank is hot enough the propane heater won't turn on at all, or it may turn on for a short time to raise the temperature a few degrees. Basically the heat pump will just heat the tank, the tank will be used to heat the house. Which means the tank will be a buffer that stores heat. The heat pump will turn on and off according to what the tank needs, not the house. I am hoping it cuts my propane fuel bill way back.

My propane water heater is only a few years old, so I don't want the expense of replacing it now; however, when it does need replacing, I may get a small propane on demand water heater and connect it to the DHW side and leave the space heating (radiant floor heat) to the lower temps that the heat pump and solar can put out.

Do you think the 30gpm minimum, that the heat pumps are rated at, would be a problem? Would a standard in tank heat exchanger be sufficient? Do you think the compressor on a pool heat pump is smaller and not able to acheive 440psi?

I guess I have more questions than anything else. It seems like the technology of air source heat pump to water is not new at all, the technology has been around a long time actually. The Daikens may use a newer technology that makes them even more efficient, but the pool heat pumps are still very efficient (and a lot cheaper) in my opinion.

I think I need to do more research.

[Xringer]

What is 30 GPM? 1/2 gallon per second? Seems like a lot, but I guess it depends
on your HX.. Flow rate, BTUh etc.
Wow! A 120 gallon tank could be pumped out within 4 minutes.. That seems fast.

I looked at those pool heater ASHP units once, but I can't recall if they were inverter models or not..
That can make a big difference in efficiency.

If you used a pool heater ASHP to pre-heat a 120 gallon water tank, feeding your
gas hot water heater, it could reduce your propane bill quite a bit.
You need to do the math, to see how much. $Propane - $kWh+cost of ASHP.
My guess is, a unit designed to heat a small pool would not be working
very much to keep a 120 gallon tank warmed up..
But, if you were pulling a lot of heat out for space heating, it could run into some serious Kwhs..

For years, we used an 84 gallon tank with four large hotwater Novan solar collectors
to pre-heat the water going into my oil boiler.
On good days, the solar tank would get up over 120 deg F and the boiler
wouldn't come on while I was taking a shower etc.

Your weather there looks idea for using ASHP for heating or DHW..

But, Solar looks like a poor prospect.. (Except on June 17)..



I'm not going to be much help, you are kinda going into an area of DIY
where not too many have gone before..

Please start a thread up on your project. Even if you don't start putting it
together, you can post your ideas (diagrams etc) and links to equipment
that's under consideration etc.

Since my roof is off-limits, I've been thinking of an ASHP to heat the
water (76 gallons) in my old oil burner, during the summer, when it's easier.

Right now, it runs every morning for 20-30 minutes and provides enough
hotwater for the day (in most cases).
There is also a little extra heat coming into it from some PV, when it's sunny.
http://ecorenovator.org/forum/solar-...l-working.html

I'm thinking maybe an ASHP pool heater would do the trick for most of the year.
We may be able to save about 120 gallons of oil a year ($470).

And, if it worked really well.. I would pull the oil tank right out of the house
and use some other method of back-up..
The boiler can take wood or coal.. (or junk mail)..

[Student 07]

Hi Xringer,

Yeah 30gpm is a lot of flow, but you have to remember this is designed for a swimming pool with hundreds of gallons to be heated. I just don't know how it would do with a 120gl tank. I suppose with a large enough heat exchanger I would be able to get enough heat out of the ASHP at that high flow rate, but I think the exchanger would be huge.

Here is a unit that can go down to 20gpm.
Aquatherm Heat Pump Specifications



Aquatherm AT105
Specifications

For small to medium size residentials pools and spas


HEAT OUTPUT (BTU/HR*)
Florida Rating @ 80º F*
ARI Stand. 1160 Rating @80 F
US Average Rating @ 50º F 101,000
93,000
63,00
COEFFICIENT OF PERFORMANCE
Florida Rating @ 80º F*
ARI Stand. 1160 Rating @80ºF
US Average Rating @ 50º F 6.0
5.7
4.0
Compressor Scroll
Voltage/HZ 208V-230V/60HZ
Phase 1 PH
Min/Max Breaker 40/60
Min/Max Water Flow 20/70 GPM
Minimum Circuit Ampacity 39
Dimensions 34"H x31"W x35"L
Shipping Weight (approximately) 325 lbs.
For Pool Sizes 12x24 to 16x32
For Surface Area (sq ft) 288 - 512
SPECIFICATIONS MAY CHANGE WITHOUT NOTICE
*Outside the scope of ARI Standard 1160
** Rated in accordance with ARI Standard 1160



You're right about our climate, it is very moderate, so an ASHP should work well. I just can't justify the expense of a geothermal system. I got a qoute one time of $45,000 for a 5 ton vertical well geothermal system.

As you can see from our weather I don't expect much out of a solar system; however, it should be able to supply enough heat for 2 months out of the year, which will help. Plus if I make the collectors myself I won't have much money into it. I consider solar in our area to be an unreliable supplemental heat source.

I am guesstimating that I would be able to use the ASHP for 9 months, the solar for 2 months and propane for 1 month.

It seems like a pool heater should work, but I am sure it will take some "tweaks". I still have a lot to learn. Maybe when I get some more information I will start a new thread, but for now I need to keep my foot out of my mouth.

I like your heating system that uses electricity, oil and wood. I think supplemental heat is the wave of the future. Using only one heat source is setting yourself up for failure. The more alternatives you have the better.

I don't think the pool heaters are using inverter technology, some of them have a 2 speed compressor. I have lots of research to do.

[Xringer]

Those specs look very power hoggish to me.. 39 amps is a LOT of current.
Not going to be cheap to run one of those monsters.

Yeah, those pool heaters on Ebay look like the very same ones we discussed a couple years ago..
Nothing really high tech about them..
http://ecorenovator.org/forum/applia...-55-k-btu.html

A couple of months ago, when I was trying to repair a 24,000 BTUh outdoor unit (ODU),
http://ecorenovator.org/forum/geothe...r-project.html
I was seriously considering trying to use it to heat our DHW.. The controller board
inside the ODU has a test mode jumper (T-Run) that allows the ODU to run without
the Indoor unit (IDU) connected.
It was looking pretty good for a while. During cooling mode it worked fine,
but when I tried to heat some water, the power consumption doubled.
I had no idea why. But, it meant that T-Mode heating was a power-hog,
and that got me worried enough to abandon the idea..

Plus, the cost of adding a brand new IDU wasn't much more than the DHW idea..
Now, that we have two Sanyos running, I'm very glad we made that choice.
If Sanyo#2 burns out it's compressor tonight, I'll be shopping for a new
Mini-split to replace it ASAP. Maybe a 12,000 to 18,000 BTUh model..

The unused Sanyo hardware will provide a pretty complete set of spare parts,
for Sanyo#1..

Anyways, my dream DHW system would be a small inverter mini-split ODU,
connected to an HX coil inside a 40 gallon water tank..
Since modern ODUs can work down to Zero degrees, no back-up would
be needed in most parts of the country..
But, if it did happen to get really cold for a long time, then you could just
use the grid to directly heat your 40 gallon tank..

[Student 07]

Hi,
I spoke with a representative at Aqua therm and he was very helpful. I told him of my plans to use a swimming pool /spa heat pump to supply hot water for my space heating and DHW needs.

He started by stating that their Heat pump was designed for swimming pools not water tanks. To make it work for my application would require numerous modifications. The high pressure switch would have to be changed to allow the water to get hotter, this would require modifications. Then he wasn’t sure the compressor would be able to reach a higher pressure or what it would do to longevity. The flow rate could be changed by swapping in a smaller hp motor and pump (Hopefully this would lower the required KW) . Of course all of these modifications would require that the controller would have to be modified to operate the new equipment.

You would be swapping out a lot of parts, basically building a new heat pump, and then its performance may still be questionable. I'm not real keen on the idea of spending $3000 for a new heat pump then hacking it up and hoping it works. I am beginning to think there may be better alternatives.

The mini split ODUs are designed for higher temps and are designed for residential use, so they would be ideal. I wonder if the refrigerant from a mini split could be run to a Reverse Cycle Chiller to produce hot water. Or could some other kind of heat exchanger be hooked up to the ODU?

Looks like I have more research to do.

[AC_Hacker]

Originally Posted by Student 07

...Looks like I have more research to do.

You might try searching EcoRenovator.

Someone has already done it.

-AC_Hacker

[poleikleng]

Similar experience to my first post, remote (line-of-sight) set to 76 degrees, outside temperature range 33 to 39 degrees. Inside the house temperature was 63 degrees 97/98 degrees being produced by the inside air handler. At 3:00 pm I turned off the heat pump and turned it back on, air handler was now producing in the range of 134/127 degrees, outside temperature was 39 degrees. Inside temperature of the house rose to 67 degrees. At night I set the remote to 70 degrees, this morning (7:30 am) inside temperature was 67.6 degrees, outside temperature was 34 degrees.

Trying to understand how the heat pump performed so well after I had shut it off and turned in back on yet seemingly under performed prior? I did not change any settings.

Poleikleng