roooooomie
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| 02/10/2009 8:16 AM |
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| I am insalling a desuperheater on my geo unit and was wondering if I could feed it into an electric (we dont have gas where I live) whole house sized tankless water heater system?
Is there any reason why this would be a bad idea from an economic or physical standpoint?
I have heard the eletric tankless are not really more efficient, but the appeal of endless hotwater when needed is very compelling. |
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IdahoGEO
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| 02/10/2009 10:09 AM |
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Roomie,
If you like the idea of the tankless on-demand water heater, it can work great with the desuperheater on a GEO unit. All you have to do is install a buffer tank prior to the on-demand electric water heater. Maybe something like a 50 or 85 GAL Marathon water heater (you won't power this buffer tank - don't connect power to it). The buffer tank will connected to the DSH on the GEO unit. So, anytime the GEO unit is running it'll be heating the water in the buffer tank. When you have a demand for hot water, it will flow from the buffer tank directly into the on-demand and get heated up to delivery temp. Many believe this method is the most eff. way to use a DSH on a GEO unit. The on-demand now only has to heat the water from maybe 70 - 90 degrees up to 120. It'll use MUCH less power to do so.
The main thing is to find out if the model of ele on-demand will allow / monitor entering water temps. You'll be delivering pre-heated water to it, so it should fire at only partial load - only enough to heat the water to the desired LWT. |
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You're only as good as your last install... |
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TechGromit
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| 02/10/2009 9:55 PM |
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I don't think so, The Desuperheat is circulating the hot water from the hot water heater thru the desuperheater and back into the tank. With a On demand tankless unit, there is no circulating occuring (and no tank). I guess you could run the cold water supply thru the desuperheater and to the tankless waterheater, when the system is not on, cold water would just run thru the desuperheater to the on demand waterheater when your using it and if the geo system happens to be on, you would get some pre-heating occuring, but I'm not sure. I would think with the hit or miss of the system happening to be on when your using the hot water, the benifits would be minimal at best, it may not even cover the installation cost in a reasonable amount of time.
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pyropaul99
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| 02/11/2009 7:32 AM |
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Posted By TechGromit on 02/10/2009 9:55 PM
I don't think so, The Desuperheat is circulating the hot water from the hot water heater thru the desuperheater and back into the tank. With a On demand tankless unit, there is no circulating occuring (and no tank). I guess you could run the cold water supply thru the desuperheater and to the tankless waterheater, when the system is not on, cold water would just run thru the desuperheater to the on demand waterheater when your using it and if the geo system happens to be on, you would get some pre-heating occuring, but I'm not sure. I would think with the hit or miss of the system happening to be on when your using the hot water, the benifits would be minimal at best, it may not even cover the installation cost in a reasonable amount of time.
With a tankless hot water heater it will work very well if you have the desuperheater heating a buffer tank. Obviously it wouldn't be tankless - but, in anycase, tankless just means that the water is heated on-demand rather than being stored as hot water in a tank. Since the buffer tank will be warmer than the incoming mains water, the tankless heater will have less work to do and thus will use less energy. Of course, a desuperheater would be useless for a tankless water heater without a buffer tank. Now as to whether the value of that energy saved over the lifetime of the buffer tank is less than the cost of the buffer tanks is a calculation that depends on your actual energy rates.
In my other thread response about having a gas hot water tank without a desuperheater buffer tank, my annual gas bill is now so low that even if it went to zero it would take decades to pay for a buffer tank.
As always, do the calcuations yourself to see if it's worthwhile.
Paul
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TechGromit
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| 02/11/2009 8:10 AM |
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Posted By pyropaul99 on 02/11/2009 7:32 AM
With a tankless hot water heater it will work very well if you have the desuperheater heating a buffer tank. Obviously it wouldn't be tankless - but, in anycase, tankless just means that the water is heated on-demand rather than being stored as hot water in a tank.
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pyropaul99
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| 02/11/2009 8:35 AM |
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Posted By TechGromit on 02/11/2009 8:10 AM Posted By pyropaul99 on 02/11/2009 7:32 AM
With a tankless hot water heater it will work very well if you have the desuperheater heating a buffer tank. Obviously it wouldn't be tankless - but, in anycase, tankless just means that the water is heated on-demand rather than being stored as hot water in a tank.
My concern with using this method is uneven heating of the water. Can a Tankless waterheater detect variations in the incoming water temperature and adjust it's heating accordingly? If pre-heated water is entering the tankless water heater to be heated, can it adjust when the pre-heated water is used up and cold water is entering it?
It has to be able to adjust - the incoming mains water is at different temperatures depending on the time of the year so it must be able to detect this. The only thing to check is the manufacturer's recommendations for the maximum input water temperature (since there is a probably a minimum power level the tankless heater operates at and if the incoming water is too hot, the output may end up being too hot). As for the incoming water temperature varying during operation, this surely happens with mains water anyway as the "dead leg" in the cold water pipe could be at room temperature and then cool down to near freezing point for mains water in the winter (at least, where I am, it's only a few degrees above freezing).
Paul.
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senecarr
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| 02/11/2009 11:09 AM |
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I seem to recall Brock had or looked at this setup at one point and had the problem that the tankless didn't fire because it saw the preheat tank as warm enough. Basically if you don't already have a tankless water heater, installing one on top of your geo has negligible return value. Basically you'll be going from a 200-400% efficient geo preheat up to ~100 or 110 F, and 90-95% efficient electric heating for the rest of the temperature difference to 99.9% for efficient for the rest of the difference. In the mean time, you have the huge cost difference in a tankless system plus, the hidden cost of the sucker probably needs its own 100 to 200 amp electric service. Where I'm at, if you need to upgrade your electric service, that's a $1000 right there, but I'm told we actually have pretty cheap rates for line upgrades.
If you want to never run out of water, just look into having your tank and buffer tank be 100 or 120 gallons. Its a much better payback for the fact that you'll have nearly limitless hot water instead of "truly unlimited" hot water. |
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pyropaul99
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| 02/11/2009 11:18 AM |
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I you really want limitless hot water in a shower a good bang-for-the-buck is a drain water heat recovery unit.
http://www.watercycles.ca/index.php
http://www.gfxstar.ca/englishindex.html
http://www.renewability.com/powerpipe.htm
http://web.mac.com/winstonworks/http%3A__www.inventure.ca/Drainergy.html
These will save no matter how you heat your water.
Paul.
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senecarr
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| 02/11/2009 12:03 PM |
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Posted By pyropaul99 on 02/11/2009 11:18 AM
I you really want limitless hot water in a shower a good bang-for-the-buck is a drain water heat recovery unit.
http://www.watercycles.ca/index.php
http://www.gfxstar.ca/englishindex.html
http://www.renewability.com/powerpipe.htm
http://web.mac.com/winstonworks/http%3A__www.inventure.ca/Drainergy.html
These will save no matter how you heat your water.
Paul.
Wow, that is pretty interesting. Not sure about payback once you've already got geothermal, but basically looks like this is of form of heat pump that works on drain water. I think I once also espoused the cheapest way to get savings out of your shower and bath's heat is to leave the drain in until the water becomes room temperature. All it takes is a $.10 bath plug drain. Of course, the system stops working in cooling season.
In all seriousness, I think I should bookmark one of these. At some point I'd like to setup instant hot water piping and these kinds of systems look like they'd be awesome to install in conjunction with that.
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pyropaul99
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| 02/11/2009 12:40 PM |
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The drain water heat recovery units are not heatpumps, they're just passive heat exchangers. The more showers you have, the more they save. I know of gyms in Montreal that installed these and they paid for themselves in less than a year. The last link I posted also has systems that work with intermittent flow devices such as dishwashers and washing machines.
Paul. |
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kiphorn
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| 02/11/2009 2:23 PM |
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| How close does the drain line need to be to the water heater? My drain lines from the two showers are on the opposite end of the house from the water heater. The drain line runs through an unheated basement that is typically around 54º. I can't imagine there'd be much heat in the water after flowing through 30' of 54º pipe. |
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Kip Horn
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Brock
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| 02/11/2009 2:27 PM |
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I can't speak for every instant hot water heater but as Senecarr said in our last house we had one and there was that magic temperature that the instant would not kick on and the pre-heat tank was not hot enough for a shower. If the preheat tank was hot, it was fine the instant would never kick on, just passing the hot water through. If the pre-heat tank was cold that was fine as well because the instant would kick on. There was just that magic time in between, while you were taking a shower and it was slowly getting cooler and cooler, to the point of not being able to stay in the water and BAM the instant would kick in and you would have to jump back and re-adjust the temp back cooler. It was a pain.
We do have a GFX drain water heat recovery unit and like it a lot. It warms the incoming cold water to the shower as well as the water going to our preheat tank for the geothermal. It warms the water about 12F as they pass raising it from winter temps of about 45F to 57F. |
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Green Bay, WI. - 4 ton horizontal, 16k gallon indoor pool, 1.8kw solar PV setup, 3400 sq ft |
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pyropaul99
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| 02/11/2009 2:29 PM |
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You can arrange the cold feed to the shower to be pass through the heat exchanger - then the thermostatic valve in your shower reduces the flow of hot water as the cold water gets warmer. Ideally you want the heat exchanger as close to the source of drain water heat as possible and ideally as close to the hot water tank as possible too. If you can't insulate your drain line through your unheated basement, you're right in that it won't be as effective. If you can do the close-to-the-shower trick though that's better than nothing.
Paul. |
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joe.ami
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| 02/11/2009 8:37 PM |
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As Seneca pointed out an on demand electric may require more service than your heat pump. You will pay a very pretty penny for "limitless" hot water and are not likely to find it in electric on demand. Look at some storage electric (which can give you as long a shower as you want), and a modest amount of stand by loss will save you thousands.
Joe |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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geodean
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| 02/12/2009 7:23 AM |
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Posted By pyropaul99 on 02/11/2009 11:18 AM
I you really want limitless hot water in a shower a good bang-for-the-buck is a drain water heat recovery unit.
http://www.watercycles.ca/index.php
http://www.gfxstar.ca/englishindex.html
http://www.renewability.com/powerpipe.htm
http://web.mac.com/winstonworks/http%3A__www.inventure.ca/Drainergy.html
These will save no matter how you heat your water.
Paul.
Paul,
Do you have one of these installed?
If so, which brand and where did you buy it?
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Dewayne Dean
PalaceGeothermal.com
Why settle for 90% when you can have 400%
We heat and cool with dirt!
visit- http://welserver.com/WEL0114/- to see my system |
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pyropaul99
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| 02/12/2009 7:37 AM |
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I don't have one installed - my energy consumption for hot water heating is so low thanks to the desuperheater that it wouldn't be worth it for me. If I had a larger family that had lots of showers then it would be more interesting. The last link I posted http://web.mac.com/winstonworks/http%3A__www.inventure.ca/Drainergy.html is a small company run by a friend of mine - and he has the only intermittent systems that I've seen - so I would obviously suggest giving him a call :) That said, they're all quite similar and it wouldn't be hard to make one yourself - the trick is getting good thermal contact with the drainpipe and a long enough path that the incoming cold water has chance to pick up heat. If you can run the drain horizontally and loop the cold water pipe around the drain (and a copper drain pipe works best obviously) then that would be best. Some of the systems above use a flattened pipe that's coiled around the drain so as to get as large a contact area as possible. If you have some pipeworking tools it wouldn't be hard to roll your own.
Hope this helps,
Paul. |
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Brock
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| 02/12/2009 10:10 AM |
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Here is a picture of our last one.
If your bored you can see ours in this short video I made in our new house of the "shop" along with all the other stuff in there. |
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Green Bay, WI. - 4 ton horizontal, 16k gallon indoor pool, 1.8kw solar PV setup, 3400 sq ft |
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TechGromit
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| 02/12/2009 11:22 AM |
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Posted By Brock on 02/11/2009 2:27 PM We do have a GFX drain water heat recovery unit and like it a lot. It warms the incoming cold water to the shower as well as the water going to our preheat tank for the geothermal. It warms the water about 12F as they pass raising it from winter temps of about 45F to 57F.
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pyropaul99
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| 02/12/2009 11:34 AM |
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It wraps around the outside of the drain pipe so there's nothing to clog nor anything to clean. Take a look at those links I posted - it should be pretty clear.
Paul.
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Brock
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| 02/12/2009 11:43 AM |
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Ours is 4 inch. Basically there was a 4 inch drain pipe from the main floor of our house that passed right next to the pre heat tank. They simply cut out the section of 4 inch drain and put this in that place. The inside is a 4 inch copper pipe with the dual 1/2 inch copper wrapped around it. So you really have two layers of copper between the potable water and drain water and if it were to leak, it would spray out at pressure, so again noting could get in to the potable water supply. It took me forever to convince our plumbing inspector it was safe. He finally agreed when I showed him the state rebate for being an energy star approved appliance (with a whopping $25 rebate)
Anyway I wouldn't think it would plug being vertical and 4 inch although there is a cleanout above and below it, if I ever need to. Our last house had one for 4 year and we never had an issue.
The only concern was with pressure drop, it is basically 3/4 inch that splits to dual 1/2 inch pipes that wrap the big 4 inch pipe. Our plumber was concerned if you had 2 showers going along with a sink or two you might notice reduced flow. Not because of the size of pipes, just adding the length of copper tubing. I assured him it would be fine and I would never complain about the flow and they reluctantly installed it. One day we stopped by during construction and there were 5 or 6 plumbing trucks in the driveway, I went down to the basement and sure enough they were all looking at the GFX and seemed to think it might actually work ;) They also though they could make them up themselves and sell them for less than what I paid. Oh well... |
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Green Bay, WI. - 4 ton horizontal, 16k gallon indoor pool, 1.8kw solar PV setup, 3400 sq ft |
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