Asorption heat pumps?

Telco · January 2010

How do folks, long time no yak...

It's getting to be time for me to put some serious work into a new house design. The kids are out of the house and the house goes up for sale in the next two weeks. Land has been bought and I'll be having it prepped for building in the next year, so it's time to get cracking. Now that I'm getting to the point of being able to build I'll try to start posting more often.

I just stumbled across something I've not seen before, on the US DOE website, the absorption heat pump. It looks like a heat pump that uses heat for the compression cycle instead of a mechanical pump, and is supposed to be more efficient than a standard heat pump since the only electricity they use is for a couple of small pumps. Has anyone seen one of these for sale anywhere? The DOE is saying they are well suited for natural gas, but should also work with solar power, so if this is an option for air conditioning I'd love to include one in the plans.

I already intend to have a heat factory to the side of the house using a shed with the southern wall made of solar water heaters, the idea being to keep a tank of around 3000 to 4000 gallons of water hot year round. This was looking like it might be a waste in the summer, but would provide domestic hot water year round and radiant heat in the winter. If there's a way to use this heat to cool the house in the summer, so much the better. If the grunt work of compression is done with solar heated water and the only electrical power needed is to run the pumps (and the way they talk this system is designed for sites with NO electricity available) then it should be well suited for a solar run house. Might even be able to incorporate a fridge into the mix.

Thanks for any information.

icarus · January 2010

Re: Asorption heat pumps?

It sounds like an interesting idea. I know nothing about using absorption for A/C, but a little bit about it in fridges. I know in an ammonia absorption fridge the temperature that is require to boil the ammonia concentration is quite high, something in the neighbourhood of ~200+f if memory serves. (I confess to knowing the real number) So whether or not hot water is going to be hot enough to boil and circulate the coolant might be problematic. I know from experience that it takes ~1500 btus to boil and circ the coolant in a fridge. Now an interesting question would be, if the circulation was aided by a pump, if it would take as many BTUs.

I don't know for a fact, but I have been told that on a per BTU basis, compressor fridges are more efficient. Others will have to chime in on that subject.

Tony

icarus · January 2010

Re: Asorption heat pumps?

Once again, living proof of why this forum is so valuable! Looking at my own answer, makes me look deeper into the issue, opens my eyes to whole new vistas!

"Adsorption Chillers are a different approach to achieving air conditioning and process cooling. Adsorption Chillers are driven by hot water rather than from large amounts of electricity like conventional air conditioners. This hot water may come from any number of industrial sources. There are no CFCs or freons, no lithium bromide, and no ammonia. By replacing the corrosive salt desiccant with a benign silica gel, adsorption chillers significantly reduce maintenance and upkeep costs
Another variant uses air, water, and a salt water solution. As shown in the figure below, warm moist air is passed through a sprayed solution of salt water. The spray lowers the humidity. The less humid warm air is then passed through an evaporative cooler which cools and re-humidifies. Humidity is removed from the cooled air with another spray of salt solution. The salt solution is regenerated by heating it under low pressure, causing water to evaporate. The water evaporated from the salt solution is re-condensed, and rerouted back to the evaporative cooler."

From Wiki.

Shows how much I know!

T

Telco · January 2010

Re: Absorption heat pumps?

Yeah, exiting, isn't it? Imagine an air conditioner that will cool a 4000 sq ft house on one, maybe two solar panels for electricity. I was thinking about maybe a freezer on a thermostat to chill water to about 40 degrees and doing radiant cooling, but then I saw this. We are planning on an air exchanger anyway to keep fresh air flowing in the house, so if we could incorporate a heat pump for cooling the house it would save some cash and complexity. We are planning on radiant heating now, but if a heat pump would do it I'd have no problems with ditching that too.

russ · January 2010

Re: Asorption heat pumps?

Yes - oh so exciting! - you aren't going to do anything with a couple of panels.

The energy consumption (be it as hot water or electricity) won't be all that different.

russ · January 2010

Re: Asorption heat pumps?

To use a radiant heat system to cool you about have to add fan coils for that purpose. Not a good idea to use the loops in a floor for cooling.

To get enough hot water to be of use for a heating system İ found you would really need to go to a concentrator system. The output from flat panel or vac tube systems are just not enough to be of use. 3000 gallons equals over 11,000 liters - at 200 liters per panel per day that takes upwards of 55 or 60 panels - not cheap!

icarus · January 2010

Re: Asorption heat pumps?

russ wrote: »

Yes - oh so exciting! - you aren't going to do anything with a couple of panels.

The energy consumption (be it as hot water or electricity) won't be all that different.

The energy consumption may not be much different, but the source of the energy would be. Solar hot water is way more efficient to "make" than PV on a per BTU basis. So using stored hot water to run an absorption cooler is likely to be way more efficient than you suggest.

If all you are doing is running a series of pumps and fans, the electrical requirement is likely to be pretty small. (relatively).

Tony

Telco · January 2010

Re: Absorption heat pumps?

Yes, as I gather one of these things is supposed to use 60 percent less electricity than a regular air conditioning system since it uses heat (they call for natural gas but can use solar) for the compression cycle. The compressor is what uses most of the power, so you'd only need a low power fluid pump to move water through the system and to keep the coolant moving. So while the energy use would be the same, the number of electricity generating panels needed would be way less seeing as not all the energy being used is electrical. As long as the minimum temperature is achieved the system isn't going to care if the heat comes from a pollution source or from the Sun. I'm still wanting to do the solar shed for hot water generation, and an absorption heat pump or even absorption chiller would be an ideal way to use solar energy collected by water in the summertime when a system sized to heat a 1500-1600 sq ft house and a 800-1000 sq ft shop with radiant heat would be expected to do is heat my domestic hot water taps.

Unfortunately, I've not been able to find anyone selling these things on the web anywhere, at least not at the residential level. I'm still trying to dig something up. I'd like for this to be a working, viable product but until I come across sites that sell them like you can find for standard AC systems I can't say for certain that this is viable yet.

On the radiant cooling system, the idea is the same as radiant heat but the pipes are put into the ceiling. Heat rises to the piping, the cold water absorbs the heat and carries it away. Apparently the systems have been in use in Europe for 15 years, so this isn't a what if this would work thing, it's an actual product.

BB. · January 2010

Re: Asorption heat pumps?

This looks like MFG of the capillary tubing:

www.bekausa.com

Interesting.

-Bill

russ · February 2010

Re: Asorption heat pumps?

A lot of things have been sold around the world for 15 years and have been bad or even stupid. Try Thalomide for one.

One major problem with radiant cooling is having condensation where you don't want it. İ have had people try to sell me the concept for my new home but check up on it. There are problems.

Anyone can make a web site and make something sound good. Radiant cooling is not recommended for in floor heating and in the walls or ceiling would be even bigger problems. You want to stay above 17 deg C (62) in the floors, ceilings or walls İ understand.

İf you have a well and ground water in the 10 degree C (50F) range you are possibly all set for fan coils. You get much warmer than that and you don't have the delta T to get the heat exchange normally required.

What İ ended up installing was a air to water heat pump, in floor radiant for heating and fan coils for heating or cooling. The in floor radiant is redundant but İ like the warm floors. Our ground water temp is 16 deg C (61 F). The fan coils have their own drains to control the condensation.

İ still have the sample section of the cooling grid in the storage room matter of fact.

İ have never heard of anyone, grid connected, proposing using PV electric power for heat - that would really get expensive!

icarus · February 2010

Re: Asorption heat pumps?

Russ,

I think there is considerable difference between radiant cooling vs absorption cooling. If you follow the link you will see that you are talking about apples and the OP is talking oranges.

russ · February 2010

Re: Asorption heat pumps?

The link in Telco's last post is for Radiant Cooling Corp
RADIANT COOLING AND RADIANT HEATING

Take a look - this is what İ was talking about.

So is the Bekausa link.

icarus · February 2010

Re: Asorption heat pumps?

Sorry, right you are. Somewhere the thread morphed from absorption cooling to radiant cooling, as I understand is two different technologies. I thought there was a link to a hot water absorption system in the thread, it seems I was wrong.

That said, I understand intuitively the concept of radiant/evaporative cooling, I am curious about using hot water for absorption cooling. Everyone who comes to visit asks how the fridge can take fire and "make cold"! The idea of taking solar heated water and using the captured energy to "make cold" is pretty cool.

Sorry for any confusion

Tony

BB. · February 2010

Re: Asorption heat pumps?

I agree with Russ about the questions for "Radiant Cooling" (tubing buried in walls/ceilings running cool water). Mold and mildew really sound like an issue in almost any sealed home/non-desert environment. The link I provided even included a moisture sensor buried in the ceiling panels (don't know if leak detection or actual humidity control/shutoff).

Absorption chillers, when I looked a few months ago, seem to make commercial sense when natural gas is cheap vs cost of electricity--not sure that solar hot water was really hot enough--at least not easy to find vendors selling such a system.

-Bill

russ · February 2010

Re: Asorption heat pumps?

İ have to follow up on this too. İ have been looking for some practical way to use solar. We have zero subsidies or incentives here plus a hefty import duty so PV is out of the picture.

The solar thermal hot water system we have İ like and is useful - maybe in another month İ will turn off the electric backup to the system then free hot water (minus a small recirc pump) until November.

russ · February 2010

Re: Asorption heat pumps?

From the DOE

'The efficiency of air-source absorption coolers and heat pumps is indicated by their coefficient of performance (COP). COP is the ratio of either heat removed (for cooling) or heat provided (for heating) in Btu per Btu of energy input. Look for a heating efficiency of 1.2 COP or greater and a cooling efficiency of 0.7 COP or greater.'

The COP's make it sound kind of dead in the water for me.

Solar Guppy · February 2010

Re: Asorption heat pumps?

russ wrote: »

From the DOE

'The efficiency of air-source absorption coolers and heat pumps is indicated by their coefficient of performance (COP). COP is the ratio of either heat removed (for cooling) or heat provided (for heating) in Btu per Btu of energy input. Look for a heating efficiency of 1.2 COP or greater and a cooling efficiency of 0.7 COP or greater.'

The COP's make it sound kind of dead in the water for me.

Your not using electric though, your using thermal btu's which are very easy and efficient to harvest ... BIG difference that say an air source heat pump that is converting electric to thermal ..

icarus · February 2010

Re: Asorption heat pumps?

Solar Guppy wrote: »

Your not using electric though, your using thermal btu's which are very easy and efficient to harvest ... BIG difference that say an air source heat pump that is converting electric to thermal ..

BINGO!!!

Tony

Gotta fill 18 letters!

russ · February 2010

Re: Asorption heat pumps?

Most web sites simply repeat the DOE information with nothing additional - kind of useless!

İtems İ did come across:

Efficient absorption chillers require water of at least 190 °F (88 °C).

One web site with some numbers follows - working out what it means:
http://www.solarpanelsplus.com/solar-air-conditioning/yazaki-solar-data.html

peterako · February 2010

Re: Asorption heat pumps?

Hi there,

Russ i do not agree whit your statements.
I have radiant floor heating and cooling ( yes cooling ) in Greece. Yes clearly it does not work if you are having condensation problems in the summer. We have dry summers and the cooling is only dropping the temp. a few degrees but i am using the ground temp. 2.5 meter deep and have a circulation pump running on 9 to 11 Watt. We have hot dry summers 40 to 42 C but in my house i keep the temp. max 30 C and that for only 9 to 11 W.

I agree it does not work every where. I hope this summer to install a solar wall to help heat the house

Greetings from Greece

LucMan · February 2010

Re: Asorption heat pumps?

www.yazakienergy.com/waterfired.htm

This system will work with solar thermal. Evacuated tubes would be your best bet as they should get the water temp. up to 160+ degrees F. Flat plate panels won't get the job done for this application.
Only draw back is that the smallest unit made is a 10 ton (120,000 BTU) and this is the only manufacturer that makes any thing this small.
At this time Absorption refrigeration equipment capacity is either very small (less than 1 ton) or large (350 tons and up) with very little in between.

russ · February 2010

Re: Asorption heat pumps?

@Peterako - We are saying the same thing - you just happen to have a situation with not so cool ground water where the pieces fit.

You have a hot situation where you are doing minimum cooling and with a relatively warm ground water - maybe 16 degrees - that is what İ have. With 10 degree water it would be different.

You will most likely not have a condensation problem due to the higher temperatures involved. Most of the people reading this will be looking for more cooling and that requires lower water temperatures - hence condensation potential.

Last summer İ managed quite nicely with natural breezes here on the gulf of İzmir. Didn't turn on the AC one time.

@LucMan - how much 170 degree water? Bunches - by the time you put up evacuated tube collectors for the volume the whole thing does not look so good.

peterako · February 2010

Re: Asorption heat pumps?

Russ.

Gulf of İzmir must have nearly the same climate as mine i am on the east side from Athens. There is just a little water in between.

Back to thread i am also thinking to use asorption heat pumps, i have already the ground loops but until this moment i dit not found in Greece somebody suppling a system.

Greetings from Greece

System2 · February 2010

Re: Asorption heat pumps?

One of the best resources you will find for zero emission HVAC design can be found at:

http://www.solardecathlon.org/

A good screening tool to evaluate systems is the winners of several key categories for example the "Hot Water" & "comfort zone" categories.

http://www.solardecathlon.org/scoring/standing_by_competition.cfm

You can examine construction drawings and mechanical drawings (for every project) along with engineering justifications for the systems chosen. You will find absorption chillers in these projects.

The take home from several years of research re zero emission design is this:

1. Design HVAC around a heat pump NOT solar hot water; Reason: solar hot water REQUIRES a backup hvac system in every case, therefore, you pay for and install two systems (solar hot water and your backup) which then must work seamlessly requiring expensive, extensive and potentially troublesome control systems.

2. Use the money you saved by not installing solar hot water to increase your PV system.

3. If you use solar hot water use ONLY a very simple solar heater ---> tank ---> solar heater loop that is used to preheat a domestic hot water loop and/or your heat pump loop. You can justify this system if you have multiple uses for the solar hot water e.g. ice melt etc. Use multiple tanks and take advantage of tank stratification.

The above conclusions are demonstrated by the winning designs found at the '09 Solar Decathlon; the worst hot water & heating/cooling system performance came from solar hot water systems. The best came from heat pump combos...

Design the house to be fully electric, powered by PV if this is appropriate in your area. Use new heatpump hot water heaters (GE and Bosch make them) and tankless electric in certain situations.

Design the house with both radiant floor heat AND ducting for whole house air exchanges (again use new heat pump ERV or HRV's). You can use the same ducting for your cooling in summer. Don't make the mistake of designing a home that has no ducting as you NEED clean air exchanges in a tight home design (tight, highly insulated home is must for zero emission design).

Radiant cooling can be used if your area has low humidity; the key is dew point to avoid condensation. Rather than risk this, IMO its better to run the cooled water to a fan coil and blow thru your duct system.

Good luck

Steve

icarus · February 2010

Re: Asorption heat pumps?

Steve,

Nice compilation.

It seems that your analysis would work well in "the best of all possible worlds", that is being the most efficient use of solar and solar dollars. But in the real world, it seems there are some pit falls. For example, simple solar hot water, coupled to demand gas comes at a much smaller out of pocket price than either Heat pump hot water, or direct solar hot water with electric demand back up. It also doesn't take into account issues of using other fuels such as wood for heat, or climates that are such that heat pumps either don't work well (too cold) or where you don't need A/C, too cool!

I think it just illustrates that as with many things , the right tool for the right job is the key. Also, it seems that this thread has veered away from absorption cooling more into evaporative cooling.

Tony

russ · February 2010

Re: Asorption heat pumps?

Agreed Steve - the only thing İ have different is that the only ducting is for the HRV which draws air from potentially humid areas and discharges to living areas.

The solar hot water is only for sink/bath use. Three Schueco panels would get me nowhere for space heating - not even the utility room!

The fan coils are an easy and good solution for cooling and can heat up a space more rapidly than the 'in floor radiant' if needed.

İ think maybe people don't realize how little hot water (50 deg C) each panel generates - especially in the winter. İ have a 350 liter tank and in the winter, even on decent days, electrical backup is essential. The evacuated tube types give a higher temperature but no more total heat as far as İ can understand.

BB. · February 2010

Re: Asorption heat pumps?

Regarding collector types; plastic mat, glassed over insulated box, evacuated tube... From my understanding, one should choose the type of collector based on how high above ambient temperature you need the final water temperature.

For example, the plastic mat is the most efficient type for heating a swimming pool of the three. The ambient temperature and the water temperature (~82F or so) are about the same.

The evaculated tube type is best when you are aiming at very high water temperatures (160-190F or so?)... There, the insulation of the metalized vacuum tubes prevents heat loss to the ambient air/surroundings. So, it becomes more efficient by default (a plastic mat would radiate more heat than it could collect at 160F--let alone probably fail from high temperatures).

0Bill

russ · February 2010

Re: Asorption heat pumps?

@Bill - İs my reading correct that either flat plate or evacuated tube collect about the same amount of total heat? The benefit of the evacuated tube type is only that it reaches the higher temperature?

BB. · February 2010

Re: Asorption heat pumps?

Actually, I believe the answer is no... Evacuated tube collectors do not have 100% coverage (gaps between tubes)--so, they would have a handicap right from the start.

I have not had time to really go through the supporting data--but if this website is correct, the "intercept" points where various collector efficiencies "cross" are (numbers are approximate--graph, and temperatures are probably in Fahrenheit--hopefully based on actual sq.unit of installed collector):

Unglazed vs Glazed = 70% eff at ~10F delta (working temp - ambient temp)
Unglazed vs Evac Tube = 49% at ~40F delta
Glazed vs Evac Tube = 41% at ~100F delta

So, if you are looking for 140F water, then the crossover point between glazed and evac tube would be roughly (140F - 100F=) 40F ambient

-Bill

icarus · February 2010

Re: Asorption heat pumps?

Another point to consider,,,flat plate, glazed hot water collectors are very easy for DIYers to do. Unlike Evacuated tubes, nearly all the hardware is available at your local hardware store/scrap yard.

The last one I built used used patio door glass panels (@$5 etach), scrap steel plate, a few 2x4s some ply wood, and a bunch of copper pipe, which in this case was used as well, for a total cost of ~$500 including the pump and the controller. Put out ~20k btu on a spring/fall day, twice that in the summer. Enough for 2 people on average.

If you live in a moderate climate where freeze protection is not an issue then installation is a snap, no glycol heat exchanger etc. Even in freezing climates, most controllers have an anti freeze cycle that circs warm water to keep the collector from freezing. A few BTUs of waste but it works well. The last one I built survives temps near 0F with strong winds for several days. (Azell controller)

It may not be the most efficient harvester of solar energy, but cheap to build, cheap to run, cheap to maintain, providing fairly big benefit.

Tony

BB. · February 2010

Re: Asorption heat pumps?

And interesting Flat Plate vs Evac Tube--One user report I saw said that flat plate tended to melt snow from "leaking heat" and collected more heat overall because of that. Whereas evac tube tended to hold the snow (insulating blanket)...

Interesting. True? I don't know.

-Bill

Asorption heat pumps?

Comments

Categories