# Anyone look into heat-pump water heaters?  My quest for oil-free house



## cbrodsky (Jun 30, 2008)

I'm thinking more about how to go 100% oil free.  Currently we are down to about 180-200 gallons/year after putting in solar HW to shut down our boiler about 8 months per year, and using wood heat as much as possible to keep it off in shoulder periods and minimize use in winter.

The sad part of this, however, is that much of that 200 gallons is standby loss - I estimate at least 0.5 gallons/day, or about 60 gallons in that 4 month winter stretch when the boiler is on.  This really aggrevates me in that a relatively low percentage of this expensive oil I buy ever makes it into my house as heat.  But it also suggests that I could go with a low level of supplemental heating system even using electric sources and eliminate this altogether, maybe saving money in the process.

I've been thinking about domestic water heat pumps as one possible solution, coupled to radiant tubing on our first floor (not installed, but easy to do and something I'm looking at anyway for better heating efficiency) and part of our second floor (tubing installed following opening ceiling for water leak).  Two BRs would be kept at 50 on their own baseboard zone with relatively low temperature water.

There is a nicely documented study from CT where these heat pump systems seem to achieve real-world COP of around 1.8: 

http://www.cee1.org/eval/db_pdf/277.pdf

We have an unconditioned, large, and deep basement - only about 1 foot above grade.  I suspect that even with one of these systems running, we'd be unlikley to change the basement temperature much beyond ground temperature, so we should have no trouble getting good performance - consistent ambient temperature.

So if I work through this a bit, I could say that while I'm buying 200 gallons of oil a year, I'm really only getting about half that into my house as heat when accounting for combined standby and combustion efficiency losses.  This would suggest that I need about (100 gallons) (138,000 BTU/gallon) divided by (4 months)(24 hours/day)(30 days) = 4800 BTU/hr on average for the 4 winter months that I run my boiler to supplement my wood heat.  In reality, I know this will spike and drop over time, but I'm assuming that I would use a hydronic storage system to help balance this load, and would be looking at a heat source with a higher rating.

Then the question is would any of this be cost-effective?

My baseline case is just buy 200 gallons of oil.  Currently, that oil would run $800/year if I'm lucky, plus I need to maintain my entire oil boiler system which adds a lot of cost.

If I purchased equivalent of 100 gallons of oil with regular electric resistance heaters (i.e. a standard water heater) at $0.15/kwH, I'd spend about $606/year for the energy assuming 100% efficiency, and probably get about the same heat into my home as the 200 gallons of oil.  This would have next to no maintenance or complexity.  In theory it could even be done with cheap space heaters.

If I was able to realize COP of 1.8 with a heat pump system, I think this means I could drop the price to $337/year.  Probably more risk of unplanned maintenance/failure expenses, but probably still less than oil furnace.  System cost is around $2000 for a 12,500 BTU system, so about 13-14% return on investment compared to a straight resistance heater.

Anyone want to poke holes in this line of thinking or offer their thoughts?

The other options I haven't sized include adding some high efficiency vacuum tube solar arrays and relying on existing electric resistance heater as backup when those don't do the job, and/or doing a water heat exchange loop behind my woodstove, integrating it into my solar control system as a second solar array that would take heat when stove is hot.  The problem with the woodstove heating is that I'm not sure I can move that much more wood through it in the winter without burning faster/less efficiently, but I'd have to be burning at least 25% more wood to generate the required extra BTUs to supply water/radiant heating.

-Colin


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## Red Sun (Jul 1, 2008)

www.airgenerate.com.


That's a link to a nicer looking unit than Nyle's. 

However, http://www.nyletherm.com/development.htm

is developing a unit that might better help answer your questions based on their cost models or simply based upon what they have in development. 


I would compare the potential of the system under development with that of your consideration of eliminating the need for oil.

I'm at 400 gallons of oil each year and can use small electrical panel heaters this year, to eliminate the load on the system to heat small upstairs bedrooms.

http://www.eheat.us/

Or, effectively eliminate perhaps 30% of the load the one upstairs zone requires now when heating with the antiquated baseboard.

So my first question is to eliminate zones or supplement any zone in order to first eliminate the total heat required from the oil boiler.

At this point I would rather consider a forced convection solar heating unit such as the http://www.cansolair.com/index.html or similarly the http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200339375_200339375 Solar Sheet systems and avoid buying any fuel.


In eliminating zones from the oil system the best potential may well be to avoid buying any sort of fuels.

I would like nothing more than to install a pellet boiler inline with the central heat system and use a second chimney to retrofit the boiler through. Truly a Maine sort of thing to do, because a pellet boiler if economical, could be installed where firewood was once stored in a room next to the kitchen. But, given the cost of pellet boilers and the inherent hassle of escalating pellet prices along with the need for bulk delivery, it is not yet worth the effort. 

However, creating a heat loop for a radiant floor system or that one can boost the return water temperature to the boiler via a wood/pellet burner with a water jacket it would seem plausible to favor the development of smaller boiler free system.


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## cbrodsky (Jul 1, 2008)

Red Sun said:
			
		

> I'm at 400 gallons of oil each year and can use small electrical panel heaters this year, to eliminate the load on the system to heat small upstairs bedrooms.
> 
> http://www.eheat.us/
> 
> ...



If you aren't reliant on oil for domestic hot water, I think one of the biggest opportunities is find a way to strech the shoulder season where heat requirements are low - this can allow you to leave the boiler shut down altogether for more months, easily saving 15 gallons/month or more.

For period when you're using your heat a lot, dollar for dollar, electric heat could cost just as much as oil.  For example, if your oil heating system is overall 70% efficient, you need about 28 kWh to equal a gallon of oil.  Depending on your local electricity rates, you could figure out at what point oil becomes more expensive for routine use such as shutting down zones.  Or alternatively, with $4/gallon oil, electric makes sense only if you pay $0.14/kWh or less.

But in a shoulder period, your overall percentage efficiency is much lower because your boiler spends a lot of time in standby hot and waiting, but not being called upon to deliver much heat to the house.  So let's say on a given day, you use a gallon of oil, but half of that is just your standby loss to keep the boiler ready on call.  In this case, you only put half a gallon of oil into heating the house, at 70% efficient.  138,000 BTUs*0.5 gallon*0.7 efficiency = 48300 BTUs = 14 kWh.  So on a day like this with lighter use, you could spend 14 kWh to save a gallon of oil if you shut down your boiler - that will almost certainly pay off.

-Colin


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## Jerry_NJ (Jul 1, 2008)

RedSun, THANKS for the link to the airtap, looks great, one plus to add in is during the summer the unit will help dehumidify your basement, I run a dehumidifier anyway, and if I cut that off the hot water cost may just balance the saved power.  I have a geothermal hp, and it has a hot water heat, but it has not worked well due to the constricted water flow required ... uses the drain tap on the WH to both take and return water to the tank..it becomes plugged in a short time.  The airtap using a direct coil in the water tank will not have this problem.

I am checking with my power and light to see if they offer any rebate, that would do the trick for me.  Looks great on first inspection.


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## Jerry_NJ (Jul 1, 2008)

Jerry_NJ said:
			
		

> RedSun, THANKS for the link to the airtap, looks great, one plus to add in is during the summer the unit will help dehumidify your basement, I run a dehumidifier anyway, and if I cut that off the hot water cost may just balance the saved power.  I have a geothermal hp, and it has a hot water heat, but it has not worked well due to the constricted water flow required ... uses the drain tap on the WH to both take and return water to the tank..it becomes plugged in a short time.  The airtap using a direct coil in the water tank will not have this problem.
> 
> EDIT: Not sure how much of a problem the cooling of the basement in the winter will be, that could be a big drawback of "taking" heat from the basement to heat hot water during cool months.
> 
> I am checking with my power and light to see if they offer any rebate, that would do the trick for me.  Looks great on first inspection.


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## Red Sun (Jul 1, 2008)

> If you aren't reliant on oil for domestic hot water, I think one of the biggest opportunities is find a way to strech the shoulder season where heat requirements are low - this can allow you to leave the boiler shut down altogether for more months, easily saving 15 gallons/month or more.
> 
> For period when you're using your heat a lot, dollar for dollar, electric heat could cost just as much as oil.  For example, if your oil heating system is overall 70% efficient, you need about 28 kWh to equal a gallon of oil.  Depending on your local electricity rates, you could figure out at what point oil becomes more expensive for routine use such as shutting down zones.  Or alternatively, with $4/gallon oil, electric makes sense only if you pay $0.14/kWh or less.
> 
> ...



The house is built turn of the century well before any sort of modern appliance let alone electricity... However, when they built the house (~1850-1890s) and Maine winters were real, they managed to stay warm. Probably and most likely better than I've been able to do when always relying on oil. (Although, a pellet boiler fits the scope of the house really well)

The system has two domestic hot water systems. One off the boiler (on demand) and another using an electric hot water tank. In the shoulder season the electric is switched on the oil off. 

I'm with you on the cost of electric heat as a function of outdoor temperature or total consumption. However, when room size is small enough the cost per btu is significant, yet the formula regarding cost per btu does not consider the area to be heated or that the room is on the second floor... I ran two eco heaters last winter with one on all the time and the electric bill doubled ($105). The units were downstairs in order to keep a laundry room above freezing and a kitchen area to test the cost and efficiency of the heater to see if it performed as well as advertised. With the Lux plugin programmable thermostat ( http://www.luxproducts.com/default.htm ) I could manage the cost of running each unit. I'm sure I can reduce the load on the furnace in the upstairs area by supplementing the heating system with electric. Interestingly the converse of heating a space with oil versus electric is likely a function of the space (area) to be heated as it is the cost per btu.

The real problem (me) is considering the use of sensors and a micro-processor of some kind that can learn the heating system in order to propagate the correct heat source to use or that it is optimized. When I discussed with a local heating professional the existing oil system, he went right for the configuration of its plumbing. Where I had measured the total return temperatures I failed to measure the temp for each of the zones. In short, the system has one circulating pump and two taco zone valves dedicated to an antiquated Crane series 70 -- 105,000 btu oil boiler. The advise given is to add in circulaing pumps.

One leg of the downstairs zone runs only 1/2" pipe feeding two kickboard heaters in the kitchen. Perhaps a thirty five - forty foot loop. Since I cook with a microwave the kitchen is unusually cold. One question I have is how much would the entire system benefit if at all possible if I installed a pellet burner with a hot water jacket and fed that line through a heat exchanger into the return loop of the kickboard heater loop?  At today’s pellet prices I’m told to expect pellet consumption to be as much as $200/mo.. I doubt it is at all feasible to install a small scale pellet system considering the added fuel cost. 

My remaining reasoning is left therefore to think green.


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## Highbeam (Jul 1, 2008)

Thank you all for the electric heat pump links. I hadn't seen these two versions and they are quite interesting. I am not too keen on dumping the cold air into the home as both models desire indoor installations. Interesting that they use the old water heater which would leave that tank's heating system intact. Dual fuel water heater! 

The heat pumps claim 50 dB noise level. Is that about like a refrigerator? They heat to 130.

A guy could put one of these on his hot tub instead of the 8000 watt element.


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## cbrodsky (Jul 1, 2008)

Highbeam said:
			
		

> Thank you all for the electric heat pump links. I hadn't seen these two versions and they are quite interesting. I am not too keen on dumping the cold air into the home as both models desire indoor installations.



I'm thinking that if you have a below-grade basement that is un-insulated, you'll stay at 50-55 which seems to be OK.  But without that, I think the applications are limited to warmer climates as you note.


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## Jerry_NJ (Jul 1, 2008)

Sorry about my double post, the second just a quot of the first.  Maybe the moderator can remove the second post if he/she see this note.

I hadn't given much thought to the noise level, but in my basement there is a dehumidifier running much of the time in the summer, and I can live with its noise level, I have a desk and work shop in the basement and spend a lot of time there.


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## Redox (Jul 2, 2008)

Interesting question, Colin!  I suspect that you might get more answers if you repost this question in the Boiler room.  Lotsa hot water there!

I think you are on the right track in wanting to get rid of your oil burner, or at least shut it down and keep it as a backup.  It sounds like you have made some serious investment in alternative energy and are ready to take the next step.  The more load you take off your oil boiler, the less efficient it becomes and using it for DHW with a tankless coil is probably the most expensive way to generate hot water right now.  There are a lot of people who have installed a conventional electric water heater and are saving money over a tankless oil setup.  The numbers are probably real, IMHO.

HPWHs are still in their infancy right now and this is the first I've seen of the Airtap unit.  It looks like a good idea and is significantly less expensive than the Nyle unit.  It is also the first unit I've seen that puts the heat exchanger in the tank with the hot water.  Time will tell if this is a good idea as a failure of either the heat exchanger or the water tank will mean having to replace the entire unit.  I believe codes will eventually require a double wall heat exchanger as mixing refrigerant (and oil) with water isn't a good thing.  The only other unit I've seen available is the E-tech from AES and it is an add on unit similar to the Nyle.  These are the only three units I have ever found for residential use, and I have been looking for years.  Now that oil is $4 a gallon, we might be seeing more.

Being so new to the market, they don't have much of a track record yet, but I think they will.  They will definitely see more use in the southern parts of the country than up north.  Since they are not really designed for outdoor use, you will have to pull heat out of your home to put into your water heater.  I suspect that putting one in the basement is going to pull the air temperature well below 55 degrees in the winter as most seem to have about a 6000 BTU compressor in them.  That amount of cooling can drop a good size room down 20 degrees in the summer and I suspect that your basement might end up dropping into the 30-40 degree range unless you duct the cool air somewhere else.  Maybe it could be ducted into the room with the wood stove?  Just a thought.

I really wouldn't count on it to act as much of a dehumidifier as they aren't designed for this.  Most of the specs I've seen show only a few pints of capacity and your need for hot water probably won't coincide with the need for dehumidification, but anything it does is just a benefit in the summer.  In the winter, you don't really want dehumidification anyway.  I don't think it is going to have the capacity for space heating as the specs top out at 8000 BTUs or so and they are really going struggle to put out more than 120 degree water.  Stealing heat out of the basement to heat another part of the house is going to be a lost cause in the long run.

I'm not sure what the future holds for these units.  Just like a regular heat pump, their usefulness drops the further north you go and I believe a full solar system is going to be more attractive in the South.  Since you already have the solar part, I would suggest an electric water heater right now in your situation.  Install it after the solar heater for maximum efficiency and wrap it up with extra insulation and it will be very cost effective.  The extra storage is a benefit with solar anyway!

Jerry, you oughtta fix that desuperheater setup.  You are missing out on the "free" hot water.  Just put an unpowered water heater in front of your existing heater and pipe the heat pump into this new tank.  Just my .02.

Chris


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## Redox (Jul 2, 2008)

Highbeam said:
			
		

> Thank you all for the electric heat pump links. I hadn't seen these two versions and they are quite interesting. I am not too keen on dumping the cold air into the home as both models desire indoor installations. Interesting that they use the old water heater which would leave that tank's heating system intact. Dual fuel water heater!
> 
> The heat pumps claim 50 dB noise level. Is that about like a refrigerator? They heat to 130.
> 
> A guy could put one of these on his hot tub instead of the 8000 watt element.



50 dB is a LOT of noise if it is in your basement and running for hours on end.  130 F is probably the top end for these units and 100-110 is going to be more realistic for efficiency's sake.  I would use a separate heater as a preheat for your existing water heater if it's electric.  Gas would have a lot more standby loss.

8KW = 27000 BTU and these units seem to top out at 8000 BTU or so.  It will work, but you will need a heat exchanger to eliminate corrosion issues.  I'm sticking with the electric heat on the hot tub for now.  They don't really use that much heat as long as you keep the top on.  Disregard if you are having all night tub parties...

Chris


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## Jerry_NJ (Jul 2, 2008)

I hadn't thought about the risk of putting the copper tubing directly in the hot water tank, but that simple approach is what makes the AirTrap so economical.  EDIT: I did  watch the video for installing the AirTrap, and as the copper tubing is "T'ed" into the hot water exit pipe it can be removed and reinstalled in a new tank if the tank needs to be replaced.

As for getting my goe-hp working again, I hadn't given any though on an aux tank as a pre-heater, any suggestions on where to get such a tank, Chris?  The current arrangement is full stop, but I can just leave the drain stopped up as the pre-heat tank will be in series with the cold water feed.  As I can no longer flush the electric tank it may need to be replaced before long...it must be approaching 8 or 9 years old anyway.


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## cbrodsky (Jul 2, 2008)

Redox said:
			
		

> Being so new to the market, they don't have much of a track record yet, but I think they will.  They will definitely see more use in the southern parts of the country than up north.  Since they are not really designed for outdoor use, you will have to pull heat out of your home to put into your water heater.  I suspect that putting one in the basement is going to pull the air temperature well below 55 degrees in the winter as most seem to have about a 6000 BTU compressor in them.  That amount of cooling can drop a good size room down 20 degrees in the summer and I suspect that your basement might end up dropping into the 30-40 degree range unless you duct the cool air somewhere else.  Maybe it could be ducted into the room with the wood stove?  Just a thought.



This would seem to be one of the major questions that I need to do some calculations around.  The units I have been looking at are 12,500 BTUs.  Our basement is about 1,000 SF fully open, and below grade block walls with no insulation.  From what I read on here, it is fairly challenging to heat such areas with 30,000 BTU woodstoves as the heat just sinks away quickly, so this is why I'm thinking it may be even harder to cool that space with a much lower BTU compressor system.  But that is something I need to size carefully.

I run my woodstove 24x7 and still need a little extra heat on cold days, so I don't want to duct cold air into the house  I actually need a net addition of heat on some days, but probably not more than 10,000 BTUs at any given time, which has me interested in these.

Agree with comments of others that such an approach really necessitates using radiant whenever possible - then the 110-120 F water output is just about perfect.  I would assume that I'd have to go down this path throughout the first floor to make it work, and would use higher temperature resistance-heated water only when using 2nd/3rd BR heat on baseboards, and even there, it would only be low supplemental load to the wood heat that hits most of the house fairly well.

-Colin


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## Telco (Jul 2, 2008)

Is there any way to insulate the basement?  If the basement were insulated on the floor and side walls it would take far less to heat, and that heat would travel to the upper floors taking some of that load off.  You might find that the system you have is up to the task without the wood boiler, if you had a warmer buffer zone under the house.  Then all you'd need to do is address the domestic hot water.


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## cbrodsky (Jul 2, 2008)

Telco said:
			
		

> Is there any way to insulate the basement?  If the basement were insulated on the floor and side walls it would take far less to heat, and that heat would travel to the upper floors taking some of that load off.  You might find that the system you have is up to the task without the wood boiler, if you had a warmer buffer zone under the house.  Then all you'd need to do is address the domestic hot water.



Sorry I may not have been clear - our basement is intended to be unheated, and my woodstove is upstairs in the insulated house.  The floors are insulated so our heated area is completely isolated from the basement.

The problem with the heat pump water heaters is that they cool the area they're in as a byproduct of the process, so I would be counting on the basement reequilibrating through the un-insulated sub-grade walls to stay in the low 50s.  Opening a basement window to vent the cool air isn't an option because the efficiency drops as you get to sub-freezing air temperatures, and you'll have to either pull in cold replacement air from outside, or warm air you worked to heat in the house.

I just got thinking about this because I hear how hard it is to heat an uninsulated basement - so now I'm wondering if I can make the same argument the other way in my favor for this application.  Particularly since the BTU cooling output would be about a third of a typical woodstove's heating output.

-Colin


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## Jerry_NJ (Jul 2, 2008)

If your below grade basement walls (NYSoap..) is 5', say, then only about 2' of that is significantly above freezing in the dead of winter.  The freeze line in Upstate NY must be at least 3'.  So you have little or no wall sourced by the earth at 50 degrees or better in the winter.  I'd expect you'd see a noticeable drop in room temp in the basement due to HP water heater.  That may not be a problem, just reduce the efficiency of the HP, not freeze the plumbing, I'd guess, I don't have any real empirical numbers - but I do recall some study data in one of the early mentioned links that talked about drop in room temp.


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## cbrodsky (Jul 2, 2008)

Jerry_NJ said:
			
		

> If your below grade basement walls (NYSoap..) is 5', say, then only about 2' of that is significantly above freezing in the dead of winter.  The freeze line in Upstate NY must be at least 3'.  So you have little or no wall sourced by the earth at 50 degrees or better in the winter.  I'd expect you'd see a noticeable drop in room temp in the basement due to HP water heater.  That may not be a problem, just reduce the efficiency of the HP, not freeze the plumbing, I'd guess, I don't have any real empirical numbers - but I do recall some study data in one of the early mentioned links that talked about drop in room temp.



Good point - I'd guess on average we're about 6 feet below grade.  Without any heat or A/C in the basement, we stay around 50-55.  Maybe some of that is coming from the house above being warmer, and part could also be the fact that the boiler is on and likely leaks some heat to the basement.  Shutting down the boiler maybe would drop us lower if it's actually providing enough heat to overcome conductive losses out the walls.

I know the freeze lines are supposed to be fairly deep, but then again, I keep fish in a 2 1/2 foot deep pond outside the house and I usually only see this freeze a few inches thick.  I was really questioning the need to bury my porch piers over 4 feet deep 

-Colin


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## Redox (Jul 3, 2008)

Jerry_NJ said:
			
		

> I hadn't thought about the risk of putting the copper tubing directly in the hot water tank, but that simple approach is what makes the AirTrap so economical.  EDIT: I did  watch the video for installing the AirTrap, and as the copper tubing is "T'ed" into the hot water exit pipe it can be removed and reinstalled in a new tank if the tank needs to be replaced.
> 
> As for getting my goe-hp working again, I hadn't given any though on an aux tank as a pre-heater, any suggestions on where to get such a tank, Chris?  The current arrangement is full stop, but I can just leave the drain stopped up as the pre-heat tank will be in series with the cold water feed.  As I can no longer flush the electric tank it may need to be replaced before long...it must be approaching 8 or 9 years old anyway.



Wow, must have some serious minerals up there...

I would consider a 50 gal regular electric water heater as a preheat tank ahead of your regular water heater.  Let the desuperheater or heat pump warm up that tank to 100-110 or so and let your regular heater bring it up the rest of the way.  That way, if you have a heavy demand, you will still have a full heater available.  Quick and dirty, disconnect that pipe from the drain valve and tee it into the cold water inlet.  It's almost the same thing, but no chance of clogging.  

There are solar storage tanks available up to about 120 gal, but they are very expensive.  50 gallon heaters are very popular and therefore more price competitive.  You don't really need to save up an entire day's worth of hot water as the heat pump will cycle many times a day to keep up.  You just need to cover a load of laundry or a shower for maximum effectiveness.  

Chris


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## Redox (Jul 3, 2008)

NY Soapstone said:
			
		

> Redox said:
> 
> 
> 
> ...



Careful with the specifications on a heat pump as there is the heat of absorption or the cooling BTU rating and the heat of rejection or the heating BTU.  The difference will be the heat of compression and is basically motor heat.  Assuming reasonable efficiencies, that 12,000 BTU unit will absorb about 9000 BTUs of heat from the room and use about 1KW of electricity to do it.  The equivalent electric element would need about  3.5 KW to do it and give you a COP of about 3.5.  I am basing this on the typical AC compressor rating of 45/130 delta.  These are rough numbers and will depend on the compressor and heat exchangers used.

How much will this drop the temperature in your already chilly basement?  I suspect that it is proportional to the temperature rise if you were to add heat, but there will be differences.  I'll let others debate this, but if you did a heat loss calculation for the basement, you would be in the ballpark.  If 12000 BTUs raises the temp from 55 to 65, then the same amount of cooling would drop the room from 55 to 45.  That 50-55 degree number is typical in basements as the earth will moderate at this temperature below 4-6 feet in practically all areas of the country.  This is why GSHPs work in the first place!

I'm not sure why you would want to use electrically heated water in a baseboard, but it is possible.  I have never seen a heat pump used on radiant flooring, but it is also possible, though I have never found anything designed for this.  I have been considering a radiant floor in our walk out family room and I think a heat pump would be a great way to take the chill off in the spring and fall when the stove isn't lit.

Chris


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## Jerry_NJ (Jul 3, 2008)

Chris,
Thanks, I hadn't given a thought to another hot water tank in series with my existing electric water heater, but sure that would work.  What I figured would be available was a smaller insulated tank of say 10 gallons that had an upper inlet and lower outlet that would connect to the HP loop, then the tank would have a lower input (could be a tub inside the tank as is the case on water heaters) for connection to the cold water feed, and an upper outlet that would feed into the existing water heater. As to why the existing "T" in the drain of my hot water heater plugs up I don't know we don't have real "Hard" water, no stains in the sink/toilet/etc and soap lathers well, still the HP (Waterfurnace) supplies "T" that was installed in the existing water heater plugged up soon after installation, then a couple of years later I replaced the water heater, made sure the "T" was clear and reinstalled.  It plugged up rather soon too...don't remember how long it took, a few months perhaps.

Now if we were to use another water heater tank we'd be short one tap (I/O) as I see it, we'd have the known three, not the needed four.  The three being: cold in, hot out and drain.  As I think the HP heat exchanger isn't free flowing enough to handle the full flow of the hot water demand, it has to "set" on the side and pump heat into the HWT as a parallel function.  Hope this makes sense, the point is I don't see how I can use a second standard HWT as the parallel pre-heater using the HP waste heat (A/C assumed for this test).


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## Redox (Jul 3, 2008)

I don't think it really makes a difference.  The drain tap on the heater goes to the bottom of the tank just like the cold inlet.  The only difference is that there will be less of a pressure change if you are running water through the heater for the house.  I have seen gas water heaters with extra taps for space heating, but that is a different application and I'm not sure it really means much anyway.  I'd try connecting the inlet of the desuperheater to the cold inlet of the existing water heater and see how it works.  It HAS to work better than that drain that keeps plugging up, right?

My suggestion on adding another tank in front of the heater is to maximize efficiency on the desuperheater.  Having the electric element come on when the desuperheater might be able to take care of the high demand isn't as efficient.  I would also go as large as possible within reason as the preheat tank is going to even out the difference between demand and production.  Just a guess, but the average shower is going to drain that 10 gallon heater pretty quick and force you onto electric resistance sooner.  The A/C will be able to warm it up fairly quickly, but you will already be out of the shower.  More storage for the "free" heat is a good thing!  Besides, price out that 10 gallon heater; I doubt it's 1/5th the cost of a 50 gallon heater.

Chris


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## Jerry_NJ (Jul 3, 2008)

Thanks, still missing something here on the plumbing and fluid dynamics subject.  I believe the desuperheater has to have the ability to circulate water when there is no demand for water so that it can heat the stored water during slack usage periods.  The plumbing you suggest would, as I read your suggestion, pass water through the desuperheater only when there was a demand for hot water.  The desuperheater has to have a "parallel" in/out path to the storage tank, and at the bottom would be best as it would draw the cooler water into the desuper..  and if the hot output was also low, no big problem, the heat would rise.  That's the idea behind the factory method of putting a concentric pipe inside a 1/2" pipe that can be stubbed into the drain hole... with a "T" to allow draining, that's what I know know to be clogged.

My 10 gallon ideas was just a "number", thinking there may be some special small tank designed to work with a HP desuperheater.  I haven't asked Waterfurnace, I may do that.


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## Redox (Jul 4, 2008)

Jerry_NJ said:
			
		

> Thanks, still missing something here on the plumbing and fluid dynamics subject.  I believe the desuperheater has to have the ability to circulate water when there is no demand for water so that it can heat the stored water during slack usage periods.  The plumbing you suggest would, as I read your suggestion, pass water through the desuperheater only when there was a demand for hot water.  The desuperheater has to have a "parallel" in/out path to the storage tank, and at the bottom would be best as it would draw the cooler water into the desuper..  and if the hot output was also low, no big problem, the heat would rise.  That's the idea behind the *factory method of putting a concentric pipe inside a 1/2" pipe that can be stubbed into the drain hole*... with a "T" to allow draining, that's what I know know to be clogged.
> 
> My 10 gallon ideas was just a "number", thinking there may be some special small tank designed to work with a HP desuperheater.  I haven't asked Waterfurnace, I may do that.



The simplest and most straightforward way to do this is to tee into the lines going in and out of the water heater.  Cold goes into the tank as well as the DSH and hot leaves the tank and DSH, assuming the DSH has a circulator of its own.  When you are not actually using hot water, the circulator pulls water back up the dip tube on the cold inlet and returns it warmer to the top of the tank on the hot outlet.  I have no idea how you would do this without a circulator; maybe some kind of sidearm arrangement?  Could you post a pic of this concentric fitting?  I haven't seen anything like you describe.  Maybe this is why it has been clogging up?

Chris


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## Jerry_NJ (Jul 4, 2008)

Yes, a "T" could work, the DSH has a low capacity circulation pump that runs, when enabled, whenever the compressor is running.  I'll take some pics of the outside of the existing connection.  The pipes are 1/2", so the pipes have the capacity and I assume the design takes into account it is working as a circulatory in a closed storage system that is under pressure, i.e., the well pump/tank pressure.


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## Jerry_NJ (Jul 4, 2008)

Here are a couple of pictures of the connection between my electric hot water heater and my geothermal heat pump.  The two insulated pipe lines going to the right go the the HP and the line to the left is the drain line, a third use for the old drain connect on the water heater.  I suspect the drain is just the input side of the lines going to the HP.


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## Redox (Jul 5, 2008)

Nope, can't say I've ever seen anything like that before!  Is this a Waterfurnace part?  I'm not sure what the purpose is, other than to make it easier to tap into an existing heater.  Since you've had problems with it, maybe it's time for a rework?  Free heat's wasting as we speak...

Chris


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## Jerry_NJ (Jul 5, 2008)

I"m not sure how much guidance the installation firm got, but Waterfurnace provided what's at the right side of the pictures, including a desuperheater and circulation pump with a defined "in" and "out" and a suggestion that these be connected by pipes to the hot water supply, and in parallel, not series.  So, on the left, the installer put a three-way tap into the drain hole of the water heater.  This provides for water to be circulated between the HWH bottom (seem good, the hot water will rise) and the dsh while still allowing the third-way on the tap, just a hole in the portion of the tank feeding the desuperheater, with a faucet to allow draining the HWH.  As it now sets, I can open the drain faucet and nothing comes out, also nothing circulates in the dsh circuit, best I can tell.   My test method over the years has been to measure the pipe temperature, under the insulation sleeve, on the water going to the dsh and on the water being returned, assuming water was moving in the pipes.  I believe the expected delta T is only a few degrees, but I would measure none to a heat loss and concluded water was not flowing in that circuit either.


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## Redox (Jul 6, 2008)

Yep, sounds like it is stopped up to me.  I assume the ball valves were open while you were checking?  I'm not sure I would want to go disturbing it if it is 8-9 years old.  I've found the tappings on a DHWH tend to rot out after a while.  If I were you, I would consider adding a 50 gal tank in series in front of this thing and pipe the DSH into this.  That way, the heat pump can heat the entire water heater up before you even begin to use hot water.  Pull the cold water back up the dip tube through the DSH and pump it back into the outlet of the first heater.  Just for yuks, put a thermometer on the line in between the two heaters and you can see how much heat you are recovering.  I think it's possible to hit 180F on a desuperheater without much effort.

My reasoning for the second heater is to separate the electric heat from the "waste" heat.  If you were to overcirculate the cool water back up to the top of the electric heater, it might bring on the electric sooner than necessary.  At least if it doesn't work out, you will have a spare heater!

Chris


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## Jerry_NJ (Jul 6, 2008)

Thanks Chris, 

Trying to put in a "three hole" tank in front: cold in (tube to bottom of tank), hot out (top dip tube, or flush with top) and drain/flush (bottom of tank).  If I put a "T" in the cold water line into the new pre-heater tank, on the cold that has the dip tube to the bottom of the tank, I could run the other leg of that "T" to the input of the DSH.  Then I'd return the DSH to the drain hole of the new tank, here I assume the water pressure in the tank is balanced top/bottom so the DSH circulatory pump doesn't have to work against any back-pressure.  Then the hot out line would simply connect to the cold input on my regular/normal electric water heater.  This would allow me to use the full 1/2" pipe cross section area in the loop through the DSH.  Sounds like:
1) a lot of plumbing
2) should work, if the existing system can/did work as it too has to work to circulate water in/out of a tank that has water under pressure stored in it.

Here I note I never verified the original system worked, as there were no easy ways to measure...when I began to wonder and started measuring the surface temperatures of the pipes to/from the DSH I think the system was already plugged up.   Other tests I made, while my wife was away, she'd never go for periods without hot water, I turned off the hot water heater when the A/C was being used and didn't use any hot water for the whole day, then measured the hot water coming form the tank...this was all long ago, but I think the first time I did this there was some elevation in the temperature, later there was not.


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## Redox (Jul 6, 2008)

That would work, but I think it would work better if you piped the DSH back into the hot outlet.  This will promote stratification which anyone in the "Boiler Room" will tell you is a good thing when it comes to heat storage.  This way, the hottest water is always available to the regular heater.

Don't worry about the pressure difference across the DSH as the pressure is in the positive direction while you are drawing water and will only increase the flow rate, if it changes anything at all.

Chris


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## Jerry_NJ (Jul 6, 2008)

Ok, you're suggesting using "T" connections on both the top cold/in and hot/out.  I'd then run the cold to the input of the DSH and return from the DSH to the hot.  My intuitive on fluid dynamics isn't working (may not exist) well, but it seems that in the static state the DSH circulatory pump would draw water from the "T-ed" tank, not the cold feed/well, and return water to the "T-ed" hot, this water would flow back into the top of the tank as space would be available due to the water flowing to the DSH.  Then, as I'm dumping hot water in the top, where it wants to set anyway (stratify level), and drawing cooler water from the bottom of the tank where it sets (stratifies) to feed the DSH there will not be much thermal churn.  The cold feed isn't supplying any of this flow.  Now when there is a draw on the system, I suppose most of the water flowing into the DSH would be the cold water input to the "T", feeding some of the demand through the DSH and some through the "normal" dip tube into the storage tank.


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## Redox (Jul 6, 2008)

You got it!  That has to work better than what you have, IMHO.  Let us know how it works.  I'd be willing to bet that you could shut off your electric elements for the summer and coast along on waste heat!

Chris


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## Jerry_NJ (Aug 7, 2008)

I'll bring this one back.  I got around today to pulling the bottom end of my old/original water heater loop.  There is a picture of the loop a few posts back.  My main concern was how was I going to drain the water heat so that I could do sweat (solder) joints on the copper pipes.  Recalling, I could not get the spigot on the bottom to drain water, all plugged up due to the narrow channels associated with the tap that splits the one drain hole into two channels, one water out to HP, the other water back to the water heater.  One of these channels is also used by the drain spigot  As seen the the picture a few posts back the water heater HP loop has individual ball valve shut offs.  So I was able to shut down both lines.  I then drilled a small hole in one of the 1/2" pipes and when I opened the ball valve, very little water came out.  So I drilled a small hole in the other 1/2" pipe and when I turned the ball valve open, water shot out of the hole. So, I cut the pipe there, ball valve closed, and connected plastic tubbing to that pipe coming out of the ball valve and fed it over to my French Tile drain in the basement floor.  It took some time to drain the tank, but it was finally accomplished.  I then pulled the two channel tap, and took some pictures of how it is loaded with calcium (lime) whatever, it is jammed up especially the narrow channel that surrounds the center pipe with provides the other flow direction for water in/out of the tank.

I don't plan to reuse this two channel tap, so I install the simple drain spigot in the bottom drain hole.  The tank can now be drained/cleaned via that spigot.  As discussed earlier in this trhead, I plan to tap into the cold line in, a 3/4" copper pipe with shutoff, and into the hot line, another 3/4" copper pipe. I will install "T" in those pipes with a 1/2" outlet.  I'll then reuse the two ball shutoff valves, one in each line and plumb those two lines (from the Ts) to the loop going to/from my HP.  I should get that done sometime this week, and as we are still in heavy air conditioning season I will be able to test to see how much "free" heat I can capture for my hot water system.  My wife is away for a few days, so I can experiment without any worry about a cry for hot water.

Picture, full picture of three way tap, looking at the business end, end that sticks into the water tank, the area around the threads is where one of the water channels is located, it is fully coated over with deposits.  Last picture is a closer look.


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## Redox (Aug 7, 2008)

EEEEWW.  That's gross!  Are you on a well?

Looks like you found the problem.  I have never seen a fitting like this.  Have you looked at the circulator for this contraption?  I hope it's not burned up.  Maybe a drain valve in the HP loop will make future work easier?

Good luck and let us know how it works.  I want temp readings!   ;-) 

Chris


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## Jerry_NJ (Aug 7, 2008)

Hi Chris, with your change in avatar it took a while to recognize you.  That's why I'm going to tap in with 1/2" in and out.  That should not get plugged.  As for the heat exchanger, it has bee turned off for some time, years.  It could have burned up before I turned it off, but in fact some small amount of water was getting through and the HP is "processor" controlled with some active maintenance programs running. There is an indicator showing the status of the super-heat exchanger, but that may be nothing more than it is "on/off".

EDIT: the big problems I see now is cutting into the 3/4" in/out to the water heater. These pipes run against the overhead joists, no up-and-down free movement.  Trying to insert a "T" with no space to move the pipe will be problematic, I may have to break into another joint to get the freedom required.


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## Jerry_NJ (Aug 8, 2008)

Here are two pictures of the revised plumbing to connect the heat pump DWH via 1/2" pipes in/out of the existing water heater.  I reused the two ball valves, they are needed for "bleeding" the loop.  One picture shows the details of the splice into the cold and hot water pipes of the water heater.  The other picture shows how the two new lines travel to get down to the original loop plumbing going in/out of the heat pump.

The weather is not hot, so no test yet to see how well it works.  I have trouble getting my mind around the fluid dynamics involved, but it seems obvious to me that when the heat pump low capacity pump starts to pump water in the loop, it will draw water out of the cold water feed side, but that will not be water coming from the well/pump/tank as the other side of the pump goes to the hot water side of the tank where it puts "pressure" on the water in the tank.  This seems to be no different than the "factory design" that used the drain hole to talk water out and around the HP loop.  The improvement I' have is dedicated 1/2" plumbing in and out.

I note in passing I had some problems getting leak free solder (sweat) joints.  Must be old age, seems I didn't used to have any trouble.  Most joints were new pipe and fittings, a couple were reconnects to existing pipe and they don't leak.  I did clean, flux and get hot, sill some leaks that had to be redone, three times in one case.


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## Jerry_NJ (Aug 25, 2008)

Some operational data.

It hasn't been the usual hot August in NJ, so the A/C hasn't been on a lot.  I did run some A/C however, while my wife was out of town, with the electric water heater off.  The HP did provide some warm water, but never got real hot, but then the A/C was running only briefly and periodically.

My wife is home and the water heater is back on, but I did have the "need" for some A/C today so I took some temperatues of the In and Out pipes (1/2" copper - see pictures in previous post) and found with the A/C on high speed (a two speed unit) the delta temperature twas about 5 degrees (example: 105 our and 100 in) and when in low speed the delta was about 3 degrees (example:  103 out and 100 in).  I have no idea of how much water is flowing in the loop, but assume the dedicated 1/2" copper line will allow several gallons per minute.  Thus a Delta T of only a few degrees represent a sizable BTU transfer.

In any case, the design discussed on this forum was implemented and it appears to be working.  Hope the saves me enough KWH to justify the expense (an additional $30 approximately) and time, at least 3 hours given I had some trouble getting two sweat fittings to stop leaking.


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## Jerry_NJ (Sep 1, 2008)

Design Error!!

After running the connection I have shown above with pictures with the HP in A/C mode it became obvious that for some reason the water delivered to tap upstairs wasn't hot, in fact it was only warm sometimes.  Thinking on this for a while I came to the obvious, now that I see it, design error I built into the HP loop.  As you can see from the pictures the hot water tank out (hot) and in (cold) are in parallel with the heat pump loop.  So, if the A/C is running when a demand is made on the hot water some of the water delivered to the tap is derived directly from the cold water inlet to the hot water outlet, via the HP, which is not putting enough heat into the water to operate as a instant/demand hot water heater.  I will take the line off of the hot water outlet and instead return it via the drain tap at the bottom of the hot water tank.  This can be done easily by simply cutting the 1/2" copper return line from the HP at any convenient point, attach a hose outlet and put a piece of hot water rubber hose that can be used with a washing machine, for example, between this new hose tap and the hose tap on the drain valve.  If this works well I can later plumb with a more permanent line.  I say this knowing that I have used such rubber hoses on my hot water feed to our cloths washer and they have held up for many years, say 10 or so.


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