Krisps
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| 02/23/2008 10:58 AM |
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A partial benefit of a geothermal heating/cooling system is that it can be used to assist in water heating. At the same time now, tankless water heaters are getting a lot of hype. Tankless water heaters are more efficient than traditional tank heaters but there are many disadvantages (check the link below). It seems a great way to take advantage of geothermal and the energy efficiency of tankless hot water heating is a hybrid system like shown in the link below. In a hybrid system, you have both a tankless water heater a very small hot water tank. This eliminates the problems with tankless systems and allows the geothermal system to help by providing heat to the water in the small tank.
http://carbonbigfoot.blogspot.com/2007/04/hybrid-tankless-waterheater.html
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hedgehog
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Posts:45
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| 02/23/2008 11:25 AM |
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| i have a similar hybrid system currently under construcktion, however my tank is placed up stream of my tankless hot water heater, i have a 85gallon super insulated plastic hot water heater tank, i say tank because it is not ever going to be hooked up electrically, this tanks has 2 sources of heat, 1 being the desuperheater on my 3-ton forced air, i believe this is set to heat the water to 145 degrees, the second source of heat is my 2 -ton water to water geopump, it has a third heating zone which is a heat exchanger and small pump system, this will cut in when the tank temps fall below 90 degrees or so, the second source is for the parts of the year when my heating or cooling loads are not enough to allow my desuper heater to heat the tank right up. the hot water output of my tank goes to a 29KW electric tankless water heater. i chose the biggest tankless unit my electrical service would allow to make sure i had maximum capacity, and because i am a typical man and like to have the biggest and the best. this unit is not immune from all the drawbacks of tankless water heaters, because it is the biggest one in this company's line up, it also has the highest gpm cut in, my shower barley turns it on. i have got the usual complaints from my wife, i am hoping once the geothermal component of my hot water system is complete most of the issues will be addressed and my tankless will hardley ever have to turn on. this tankless water heater does sense incoming water temps and adjust the heat accordingly. another note to would be tankless water heater purchasers, although this water heater is the second largest from this company, (the 36KW they offer requires a 300amp service) it does NOT have the capacity to keep up with the roman faucet on my jacuzzi, if i throttle the faucet back to about half and do not turn the cold on i can fill the tub with hot water. i do believe natural gas models do have more capacity, i chose the electric because i do not intend to have natural gas hooked to my house. if you have any questions, fire away. |
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geodean
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Posts:816
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| 02/23/2008 11:38 AM |
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Most heat pump desuperheaters will only heat water to 120°. This only happens when the heat pump is running to provide space heating or cooling. During the spring and fall when the is no demand for heating or cooling there is no hot water assist coming from the heat pump.
It doesn't make any sense to put the storage tank after the tankless heater. The water would already be heated and the desuperheater can not add any heat.
If I was going to do this, I would have two tanks. One before the tankless that the desuperheater can pre heat and then one after the tankless for reasons described in the link in the opening post. |
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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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hedgehog
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Posts:45
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| 02/23/2008 12:44 PM |
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'Most heat pump desuperheaters will only heat water to 120°. This only happens when the heat pump is running to provide space heating or cooling. During the spring and fall when the is no demand for heating or cooling there is no hot water assist coming from the heat pump.'
this is why i added the second system to heat the water, my water to water unit will cut in just to heat my tank, only to 90 degrees or so however, this should help minimize my power consumption from my tankless and add capacity to my tankless for things such as my roman faucet. i think the second, downstream tank would be unnesasary, preheating the water goin into the tankless will eliminate the cold water 'sandwiching' described in the first post, as for speeding up hot water delivery time i have considered one of those convection flow circulating systems to each of my faucets, especially if it turns out my geo component of my hotwater system has more than enough capacity for my DHW needs. as for temps, i am not trying to argue, you are obvious the geo guru here, but on my previous 3.5 ton system i frequently saw temps well above 120 degrees from my desuper heater, i would suspect that as the storage tank water increased in tempurature, the amount of BTU's the desuper heater provides would decrease.
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geodean
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Posts:816
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| 02/23/2008 2:48 PM |
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Thanks for your input. I always want to hear what other people are doing and how they have have solved problems. We can all learn from exchanging ideas and especially hearing about what is actually working
It sounds like your system is working fine. You obviously have put a lot of thought and planning into it.
I was mostly responding to the original poster where he wanted to put the tank after the tankless. |
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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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Krisps
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Posts:10
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| 02/23/2008 7:01 PM |
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| For the case in the link I posted, I think it makes sense to have the tank after the tankless and it seems to me to be more efficient that way. The key to the link is that the tank has a low power heater and the tankless by itself provides delayed hot water and provides hot water only if there is minimal water flow (not a trickle). The tank provides some efficiency by storing just enough hot water to provide immediate hot water while the tankless gets going, and would also provide hot water even if there is just a trickle demand. This would not work as well with the tank upstream of the tankless, the tank would then require a much stronger heater, would defeat the purpose of the tankless. |
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jpanning
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Posts:1
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| 03/05/2008 2:54 PM |
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| I'm thinking about a geothermal system, and I already have a Bosch AquaStar 125FX. Since the desuperheater supplies (say) 120° water and the Bosch will raise the temperature 45-90° depending on water flow, doesn't this mean that I might have 200° water? What's to keep that from happening? |
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caja_ca
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Posts:14
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| 03/06/2008 10:36 PM |
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what is that Bosch?? is it gas?? I didn't think Bosch made a gas/propane heater they would recommend for that application. If it is electric it should have temp sensors on it to maintian the output temp.
It has been a while since I looked at bosch..but if it is gas.. I cant stress enough not to put it into a desup application...it isn't meant for it.
If they haven't change the specks I dont even think they want you running a grundfos comfort system of them or a Leang ATC303BTW even.
Electric no prob...look at a Steibel Eltron Tempra 29 |
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