Buffer tank for DSH
Last Post 29 Sep 2015 10:53 AM by docjenser. 11 Replies.
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plzenkUser is Offline
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03 Sep 2015 06:20 PM
Hi I have a question for the experts out there.i had an old water heater that I used as an buffer tank for my geo. last week the tank rusted a hole in the bottom and I shut the DSH off and unhooked all the piping off the unit. My question is is it cost efficient to buy a new water heater 40 gallon will cost around $400 will I ever get my money back in energy savings?or just leave it unhooked? Thanks
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04 Sep 2015 12:20 AM
Hot water costs are significant, people underestimate it. It depends on the amount of water you use. Family of 4, the DSH with a new buffer tank probably saves you at least $200/year, if you final tank is electric.
www.buffalogeothermalheating.com
arkie6User is Offline
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04 Sep 2015 11:36 AM
Have you checked the local Craigslist for electric water heaters? I found several new ones in the 40-60 gallon range here for <$250. Some may have minor dents or scratches in the exterior sheetmetal, but that doesn't really affect the performance as a storage tank.

Here are a couple of examples:

http://fayar.craigslist.org/app/5106488548.html

http://fayar.craigslist.org/app/5164348677.html

 
chrsUser is Offline
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04 Sep 2015 04:09 PM
What do you use for water heating when you aren't using the DSH?
plzenkUser is Offline
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04 Sep 2015 05:51 PM
I use an 50 gallon Marathon electric water heater there are two us here so we don't use a lot of hot water. Thanks
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06 Sep 2015 07:26 AM
So with two of you your savings may only be $100/yr but that is still a nice ROI
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
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06 Sep 2015 11:47 AM
Thanks for all your advice. I will pick up a water heater for buffer tank Thanks again
chrsUser is Offline
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10 Sep 2015 09:43 PM
You can also run the DSH right into the Marathon. In the summer, the DSH temperature might not be high enough to be useful, but in the winter, you can deliver a high enough temperature that you won't use the electric element in the Marathon much. That's how my system is set up and I actually turn off the electric heating element for most of the winter. How much the buffer tank matters depends on your climate--how much heating vs. cooling.
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13 Sep 2015 12:56 AM
Posted By chrs on 10 Sep 2015 09:43 PM
You can also run the DSH right into the Marathon. In the summer, the DSH temperature might not be high enough to be useful, but in the winter, you can deliver a high enough temperature that you won't use the electric element in the Marathon much. That's how my system is set up and I actually turn off the electric heating element for most of the winter. How much the buffer tank matters depends on your climate--how much heating vs. cooling.


Not a good suggestion. yes, you can shut of the electric heat element, but your response time will not be very good. Plus if you have a warmer day where the heat pump will not run enough, your hot water tank will not get heated, so you are running out of hot water.
www.buffalogeothermalheating.com
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20 Sep 2015 07:07 AM
"You can also run the DSH right into the Marathon."

People who monitor equipment find this to be a poor set-up with energy being extracted from the water heater and put in the ground in some cases.
Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort!
chrsUser is Offline
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22 Sep 2015 06:24 PM
Wow, not a lot of love for direct single-tank DSH!

Yes, for summer it's a poor setup, as I said in my initial post. Best case not useful, worst case moving heat from the DHW tank to the ground. A switch or a relay to shut if off in cooling mode is a good idea, and is cheaper than adding a tank, but it's true that adding a tank allows you to use the DSH in the summer and is better.

Re: shutting of the heating element, yes it slows response time. I see that as a good thing: it means you are using the DSH more and the electric heat less. Certainly, if the response time is not adequate for your usage and system it's a bad idea, but if it works well (for part of the season), it is all upside (for that part of the season). Mine does work well. Not all installations do. When I say it's all upside, I mean comparing with or without the heating element on, with the same single-tank setup either way.

If you compare single tank to two tank, there's no significant advantage other than cost and footprint for the single-tank system. The OP has the footprint available and there have been good suggestions about how to find a low cost tank, so in his case that's good advice. But short of getting a new tank, I still think he'd be better off running the DSH directly into the Marathon, and switching off DSH in the summer, compared to just disconnecting the DSH permanently.
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29 Sep 2015 10:53 AM
Posted By chrs on 22 Sep 2015 06:24 PM
Wow, not a lot of love for direct single-tank DSH!

Yes, for summer it's a poor setup, as I said in my initial post. Best case not useful, worst case moving heat from the DHW tank to the ground. A switch or a relay to shut if off in cooling mode is a good idea, and is cheaper than adding a tank, but it's true that adding a tank allows you to use the DSH in the summer and is better.

Re: shutting of the heating element, yes it slows response time. I see that as a good thing: it means you are using the DSH more and the electric heat less. Certainly, if the response time is not adequate for your usage and system it's a bad idea, but if it works well (for part of the season), it is all upside (for that part of the season). Mine does work well. Not all installations do. When I say it's all upside, I mean comparing with or without the heating element on, with the same single-tank setup either way.

If you compare single tank to two tank, there's no significant advantage other than cost and footprint for the single-tank system. The OP has the footprint available and there have been good suggestions about how to find a low cost tank, so in his case that's good advice. But short of getting a new tank, I still think he'd be better off running the DSH directly into the Marathon, and switching off DSH in the summer, compared to just disconnecting the DSH permanently.


DSH contribution will be minimal with single tank setup, even in heating season:
1) With single tank, entering water temp is too warm, thus not much heat is being transferred. DSH capacity decreases with higher EWT into the DSH
2) DSH 5,000 DSH competes with 15,000 BTU electric heat element. Guess who wins?
3) Cold water enters directly the hot water tank, and is permanently circulated through. Thus some mixing occurs, reducing tank temperature. Electric heat element turns on, beating the purpose of having hot water heat generated by the geo system.
Sure a crappy DSH setup is still better than no setup, but for a few hundred $$$ more you get so much more performance out of it with a 2 tank setup.
www.buffalogeothermalheating.com
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