Running a Heat Pump with Solar Electric - White Paper

[JoyfulNoise]

All,

I thought I would throw out this link to a white paper written by a local solar company here in Tucson called Engineered Solar (formerly Sun Power of Arizona). Let me say up-front that I have absolutely no affiliation with this company other than I was researching solar pool heating options and this was one company that was recommended to me. My thought originally was to do the standard thing that most folks around here with flat rooftops do - HelioCol black plastic solar collectors. I have sufficient rooftop area on my casita near the pool (~700 sq ft) for my pool (~468 sq. ft) to put up solar heating. However, the owner of the company (an instructor at the University of Arizona), wrote a white paper on the various solar heating options making certain assumptions about heating efficiency, pumping efficiency, utility costs, etc. It is here -

http://esmeps.com/images/Engineered_Solar_Pool_Heating_Options_Summary_4-15-2015.pdf

The one intriguing option I saw, which is certainly not the cheapest or fastest in terms of ROI, is installing solar electric to run a heat pump and to use that setup to collect solar energy and heat a pool slowly. I like the elegance of the idea because it eliminates the need to pump water up to a roof top and simply collects electrical power for the sun to run a heat pump. Seems interesting (and a bit pricey!!).

I would welcome anyone's additional thoughts or spit-ball throwing at the analysis.

 

[bdavis466]

Matt,

I read the paper and was impressed with what it had to say. The idea behind it is certainly intriguing and in result is making me research all that I can on heat pumps. I have never been drawn to the idea of the solar heating mats on the roof, mainly for aesthetic reasons. I really question their longevity as well since it looks like I see more and more disabled solar heaters. I would really have to take a hard look at the facts to see what my best option would be.

I've looked into the Raypaks and the Pentair UltraTemp. Pentair is winning for me since I received the hat and shirt you bought for me! It also seems like it integrates well with the Easytouch.

I am very concerned with the expense to run the heat pump. It looks like the Pentair unit draws 6 KW/H making my cost to run it over $2 per hour! It could not be done without solar. The initial expense of the heat pump is not a factor because the solar heating system I priced out was nearly double the heat pump, and that was with me doing the install.

Here is what I need to find out:

-What type of heat gains can I expect from the heat pump
-What pump speed is required to supply the heat pump
-How restrictive is the heat pump
-How loud is it
-How does ambient temperature effect its performance

I think from a pure cost standpoint, solar heating is a better option. If P/V panels are installed to not only power the heat pump and pool equipment but also the entire house, then there is a real cost savings to be seen. If the performance of the heat pump is similar to that of solar (or preferably better), I'd pull the trigger tomorrow...

 

[JoyfulNoise]

Heat pumps are like BBQ smokers - low and slow. You can think of a heat pump like an air conditioner run in reverse (actually the good ones will both heat and cool your water). You definitely want to splurge and get one with a titanium heat exchanger.

You can expect maybe a roughly 5 degree F heat rise per day ASSUMING you have a good solar blanket on the pool overnight to retain the heat. You basically run it 24/7 (or as long as it's powered) to maintain the temperature setpoint you want. You could use your gas heater to bump the temperature up faster and let the HP maintain it.

As for hydraulic losses, I would assume they would be about the same as your gas heater so you might include a bypass option on it. For pump speeds, definitely less than roof top solar and again, probably equivalent to what you use when you cut-in your gas heater.

You could start by getting enough PV at your pad to run all your pool equipment and that would save you a good chunk of change on your utility bill. Even though the HP is rated at 6kW you may not need that much AND that's likely peak power draw. Once the pool is at temperature, the power use is going to be less.

Matt

PS - You should apply to Pentair to be an area rep, then you can get all the free tee-shirts you want (plus a little kick back each year for all the sales you promote)


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[JoyfulNoise]

Missed the ambient temp question.

HP's definitely perform better at higher air temps AND higher relative humidity (well, just about anyone has higher RH than me). Once the air temps drop below 50F, heat pumps are really useless and, in dry climates, they are not as efficient. That's because moist warm air has greater heat capacity than dry warm air.

Check out this link -

Heat Pump Swimming Pool Heaters | Department of Energy

Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[bdavis466]

Intersting humidity is a good thing, I would have thought the opposite. Given your numbers above, it would seem that a heat pump and an appropriately sized solar heating setup have relatively similar heat gains. I have a good understanding of how they work, I just don't know how well they work. I'm sure there is a reason why I've never seen one around here and I'm sure that has something to do with our electric rates.

PS - You should apply to Pentair to be an area rep, then you can get all the free tee-shirts you want (plus a little kick back each year for all the sales you promote)


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

Ha! Its not so much that I'm a Pentair guy, its just what I know well. Pentair certainly has its shortcomings but overall has served me well. I've been rather impressed with the Jandy equipment recently, not enough to convert me but it did grab my attention.

I will NEVER turn down a free T-Shirt!

 

[JoyfulNoise]

I will NEVER turn down a free T-Shirt!

I think we may have been separated at birth...I've always said the same thing.

When I worked in an Italian restaurant (as a cook) in my younger days, we would harass all the specialty food vendors that did deliveries to get us free tee shirts or ball caps. They would roll their eyes at first but we were relentless at giving them grief each week. Eventually we got the tee shirts.

Fast forward to the present, when we had our backyard landscaped a few years ago, I quipped to the owner that, with all the money I was paying him, the least he could do is throw me a free tee-shirt. He came back a few days later with three baseball caps with his company logo on it and gave each of my kids one. When my oldest asked me why, I told him this bit of sage-advice -

"If someone is handing out free $20 bills, take TWO!"

Yeah, you don't see HPs where you are because they don't play well with high utility rates. But I think when they're matched with solar PVs, they are a good fit. And let's face it, the purpose of the solar heating is to extend your swim season on the elbow months. You're not going to run the HP much in the height of summer unless your water gets so hot you need to cool it. Being a fellow desert dweller, low RH means my kids shiver coming out of an 88F pool into 105F air temps with 20% RH. You can't beat evaporative cooling


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[Leebo]

Speaking from a completely different climate with entirely different power rates I'd like to chime in concerning heat pumps. We installed on this year and are shocked how well the current ones have preformed. During the hotter August months we commonly saw about a 1° increase every hour during the day. I'm sure we'll see lower heat gains in the May and October months this year due to colder weather, but there's no doubt they'll keep up. For us it only increased the power bill by about $100 a month due to our low rates, but it was MUCH cheaper compared to our only other option of a propane heater.

 

[bdavis466]

I think we may have been separated at birth...I've always said the same thing.

When I worked in an Italian restaurant (as a cook) in my younger days, we would harass all the specialty food vendors that did deliveries to get us free tee shirts or ball caps. They would roll their eyes at first but we were relentless at giving them grief each week. Eventually we got the tee shirts.

Fast forward to the present, when we had our backyard landscaped a few years ago, I quipped to the owner that, with all the money I was paying him, the least he could do is throw me a free tee-shirt. He came back a few days later with three baseball caps with his company logo on it and gave each of my kids one. When my oldest asked me why, I told him this bit of sage-advice -

"If someone is handing out free $20 bills, take TWO!"

Yeah, you don't see HPs where you are because they don't play well with high utility rates. But I think when they're matched with solar PVs, they are a good fit. And let's face it, the purpose of the solar heating is to extend your swim season on the elbow months. You're not going to run the HP much in the height of summer unless your water gets so hot you need to cool it. Being a fellow desert dweller, low RH means my kids shiver coming out of an 88F pool into 105F air temps with 20% RH. You can't beat evaporative cooling


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

I hear you there. You would think my girls were swimming with polar bears in August. 100 degrees out and they are blue and shivering!

Speaking from a completely different climate with entirely different power rates I'd like to chime in concerning heat pumps. We installed on this year and are shocked how well the current ones have preformed. During the hotter August months we commonly saw about a 1° increase every hour during the day. I'm sure we'll see lower heat gains in the May and October months this year due to colder weather, but there's no doubt they'll keep up. For us it only increased the power bill by about $100 a month due to our low rates, but it was MUCH cheaper compared to our only other option of a propane heater.

What heat pump do you have? I imagine the noise level is comparable to an Air conditioning unit?

1 degree per hour is about as much as I can expect from my gas heater, good for you guys.

 

[needsajet]

This was a tough decision for me. I did a lot of reading and calculations and really wanted to add the heat pump, given that we already have solar PV, with around 11 kWh surplus each day in the shoulder seasons. Plus, sunny or not, I could always buy electricity to heat the pool on cloudy days for much of the year. We're in a typical suburb and have amazing neighbours, so sound was a big consideration for them and us.

The solar (thermal) panels were the noise-free option, so that's what we ended up doing. The circ pump is in the same sound-proof enclosure required for the building permit.

In the back of my mind was another heat pump to maintain - it would be no. 4 for our house (ducted air con, one split system, and the fridge). It seems to me that these all used to last for 20 years and nowadays it's more like 10 years. But on the other hand, the circ pump may only go 3-5 years and who knows about the rest.

That said, just before I poured the equipment pad, I stubbed in two 1.5" lines in case we change our minds!

 

[JoyfulNoise]

This was a tough decision for me. I did a lot of reading and calculations and really wanted to add the heat pump, given that we already have solar PV, with around 11 kWh surplus each day in the shoulder seasons. Plus, sunny or not, I could always buy electricity to heat the pool on cloudy days for much of the year. We're in a typical suburb and have amazing neighbours, so sound was a big consideration for them and us.

I'm curious, in Oz do you guys have solar access laws in place?

In the US, most states have what are called solar access laws which basically make it impossible for any person or homeowners association to legally deter you from installing solar energy products (PV panels, solar heaters, etc). Early on in the solar game, too many perfectly good rooftops were being restricted by draconian HOA rules and nuisance lawsuits that made installing solar difficult.

That's really great that you have 11kWh of surplus to use. Do you sell it back to your electric utility?

 

[pooldv]

I am pretty interested in this thread and the concepts. We are green people and are big fans of efficient and renewable energy.

Some backstory. We have cheap electricity at 10.25c/kwh. We have owned a Chevy Volt and three Nissan Leafs since 2012, currently have two 2015 Leafs and am looking forward to getting a 2016 updated Volt this summer. We have a 5 ton geothermal heat pump for the house with 5 250' deep wells with 72* year round water that was installed around 1990. We will be installing a new 5 ton Climatemaster geothermal unit in about a week with VS blower, VS water pumps and much, much higher efficiency than our current Florida Heat Pump geo unit. We all know how great VS pool pumps are, the VS geo pumps use about 20% of the electricity that the old fixed speed water pumps used.

About 5 years ago I looked into solar PV panels to power some outbuildings and stuff. There was no way I could justify the expense and work needed to learn, install and operate a PV array. It is likely much better now.

Air source heat pumps are vastly more efficient than they were just a few years ago. They can now operate efficiently well below 32 degrees F and some are still relatively efficient down close to 0*F. The days of heat pumps losing efficiency at 45 degrees is over. They are so much more efficient today that we considered converting from a ground source to an air source system due to upfront cost savings. But, geo won out in the end for a number of reasons. Now, I don't know if pool heat pumps have kept up with residential heat pumps. Maybe not given the pool industry's lack of advancement in pool automation and controls.

I have discussed with various people tying our desuperheater into the pool and/or running the ground loop through a water/water exchanger for the pool. But, I cannot find anyone who knows enough to model it or has tried anything of the sort. So, either I conduct an experiment of one or I keep my geo heat pump for the house separate from whatever I use to heat the pool. We ultimately decided to heat the pool with 5 4'×12' solar panels. They help a lot and give us many swim days that we would lose to rain, shade, cool fronts, etc cooling the water. But, really that is only helpful during the season. The solar panels cannot warm the pool enough to really extend our swim season. We will need to add a lot more solar panels or a heat pump for that. We are still mulling over the benefits of that vs just getting in the hot tub.

Update: As an aside, we also primarily heat with wood in a big wood stove. Wood is currently our only source of heat since the heat pump bit the dust in December. It has been nice heating only with wood and being able to take the time to research heat pumps. If it had failed in the summer this would have been a much more urgent situation!

 

[bdavis466]

The sad reality I face is that even in the peak of summer the pool never got warm enough for my wife and kids liking. I have no issue down to about 70 degrees.

The warmest temperature my pool reached was 88 degrees and that was with several days that were over 100 degrees outside. A big factor with this is no doubt the heat loss at night since our nightime temperatures are typically fairly cool in relation to what we experience during the day.

I wish I could overcome my disgust with the appearance of a pool cover but I don't see that happening. At least I'll have the pool to myself until I decide to go with solar or a heat pump.

 

[pooldv]

We don't use a cover either. Don't like the looks or the work of putting on/off and I am also nervous about debris on the cover or brought in with the cover because we have so many trees with leaves and stuff everywhere.

We definitely like a warm pool. 80 is absolute minimum with 85-88 preferred and up to 92 is OK with us. 93 is too hot! That is where our solar panels help us the most in getting that extra few degrees to make the water comfortable instead of tolerable.

 

[bdavis466]

I wish that I had a good idea of what solar heating would do to my pool. I have high hopes, but I fear the reality is that the results will end up falling far below my expectations.

At least a heat pump could run 24/7 and produce heat unlike the solar heating that has a very limited window. I would love to see the steam rolling off my uncovered pool every morning

 

[JoyfulNoise]

I'm pricing out covers now. I initially had a pool cover and I hated it. It was a pain to take on and off and it got dirty A LOT and would spew mesquite dropping into my pool.......

BUT, I also spent an ENORMOUS amount of money last year on water. Pan evaporation rates for my area can be as much as 2-4" per day. So if you calculate it out, I basically evaporated away my entire pool volume over the summer and, with auto filling, greatly increased my CH (not to mention I made Tucson Water a very happy business).

My plan is to get a 20'x40' silvered/opaque pool cover and cut it into 2 or 3 sections and then use Mark's (mas985) DIY solar roller reel. That will help with cover removal. I'm going opaque because i'd like to cut down on FC loss and figure a good silvered cover will help retain heat and keep the UV out. If I can cut FC loss, then I can also run my pool pump less and save some energy that way. The only down side will be cover maintenance (cleaning) and removing the cover periodically during low usage to make sure the water gets some UVs on it.

If you want to ever heat your pool efficiently, then you unfortunately have to cover it. Water is thermodynamically driven to evaporate once you get even a few degrees past ambient air temps. Unless you live in a very high humidity climate, the water will cool very rapidly from evaporative heat loss.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[bdavis466]

When will you finally decide to put that big brain to use and invent an invisible cover or water that doesn't evaporate? I'm not talking about that liquid pool cover junk either.

I thought I saw Mark mention that a clear cover was the best for heat absorbtion and allowing some UV light into the pool? An opaque cover seems like a better choice for a pool heated by gas or a HP?

Heat + cheap = Ugly

Heat + beauty = $$$$$

Thats about as close to a chemical equation you will see from me :joker:

 

[Leebo]

What heat pump do you have? I imagine the noise level is comparable to an Air conditioning unit?

1 degree per hour is about as much as I can expect from my gas heater, good for you guys.

We went with this one from Raypak. It does put off about the same amount of noise as a AC unit, but we would always turn it off if we're outside at the pool. We would use a solar cover religiously during the week as all the heat gained during the day would quickly disappear overnight without it.

 

[mas985]

I thought I saw Mark mention that a clear cover was the best for heat absorbtion and allowing some UV light into the pool?

Theoretically it should be but my experience is that it wasn't any different than a transparent blue cover. Probably because a clear cover doesn't stay clear for very long and most of the heat transferred by the sun (infrared) is basically transparent by both cover colors. I did an IR test on both covers and there was virtually no difference between the two.

Also, the opaque cover would only be better if it was insulated. Otherwise, it might be worse than a bubble cover which does have some insulation.

 

[JoyfulNoise]

A "clear" bubble cover lets both heat (IR radiation) and UV light in. So if you want the sun to warm your pool, a good clear or blue bubble cover can help with that.

An opaque bubble cover, especially a silvered one, will cut off all UV from the pool water and lower the FC loss from UV degradation. It will also reflect away some IR which will cut down on some of the radiant heat input from a sunny day.

Both types of covers will lower evaporation rates which will cut heat loss in the overnight hours. This is where covers are critical for solar heating (either with collectors or a heat pump) as you need to retain heat you pumped into your pool during the daytime. So you can probably leave the pool uncovered during the day with the heat pump and sun to warm it (just keep the setpoint lower than ambient air temps). Then, at sunset, roll out the cover. Kind of like putting the kids to bed

Sorry, no magic mystery invisible covers ... yet. However, in the meantime, you can add Jello to your pool water and see how that works out for you Just be careful jumping in as you might bounce a bit and you could hit one of those lovely rocks in your pool


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

 

[bdavis466]

Theoretically it should be but my experience is that it wasn't any different than a transparent blue cover. Probably because a clear cover doesn't stay clear for very long and most of the heat transferred by the sun (infrared) is basically transparent by both cover colors. I did an IR test on both covers and there was virtually no difference between the two.

Also, the opaque cover would only be better if it was insulated. Otherwise, it might be worse than a bubble cover which does have some insulation.

So now the critical question....which one won't make me when I look at it? I swear they design those things to be hideous.

A "clear" bubble cover lets both heat (IR radiation) and UV light in. So if you want the sun to warm your pool, a good clear or blue bubble cover can help with that.

An opaque bubble cover, especially a silvered one, will cut off all UV from the pool water and lower the FC loss from UV degradation. It will also reflect away some IR which will cut down on some of the radiant heat input from a sunny day.

Both types of covers will lower evaporation rates which will cut heat loss in the overnight hours. This is where covers are critical for solar heating (either with collectors or a heat pump) as you need to retain heat you pumped into your pool during the daytime. So you can probably leave the pool uncovered during the day with the heat pump and sun to warm it (just keep the setpoint lower than ambient air temps). Then, at sunset, roll out the cover. Kind of like putting the kids to bed

Sorry, no magic mystery invisible covers ... yet. However, in the meantime, you can add Jello to your pool water and see how that works out for you Just be careful jumping in as you might bounce a bit and you could hit one of those lovely rocks in your pool


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006

Blue Jello might do the trick as long as no rocks are hurt in the process. I may even look for a water substitute like spaghetti noodles or roofing tar...this whole water thing is very overrated.