86turbodsl
New Member
Posts:45
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| 02 Jun 2009 12:45 PM |
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Hypothetical question on this setup.
Currently I have a Climatemaster water to water HP DSH dumping into my electric water heater.
I know this is not ideal.
I'm currently planning my system retrofit to include solar and buffer tanks.
Does my plan make sense?
Well pump to 40 gallon buffer (DSH dumps into here) from there to 106 gallon solar tank w/two indirect coils (one solar, one for boiler backup) from there to 40 gallon electric water heater with elements set at 140 for finishing.
My thinking was DSH provides hot water during hot times and cold times and solar provides during off seasons.
2 adults and 2 kids in house, we have a 2person hot tub in master bath that maxxes the hot water demand.
My thinking was I might need a hot water dump for solar in the summer, but at least I'm keeping the electric demand down most of the year.
Comments? |
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joe.ami
Veteran Member
Posts:4377
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| 08 Jun 2009 06:58 AM |
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Thoughts at a glance; why the boiler back-up? Get rid of that or the electric "finishing" tank.
140* is too hot for safety and 40 gallon end tank too small for hot tub.
Good luck,
Joe |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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86turbodsl
New Member
Posts:45
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| 08 Jun 2009 09:21 PM |
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The solar tank is running about 180F or so, to maximize the solar storage, the finishing tank adds total system hot storage because the
hot tub is over a 100 gallons. Electric is currently cheaper than propane, but may not always be, and the recovery sucks. In event
the electric can't keep up, the boiler can kick in and recover much faster than the electric in case the kids run me out of hot water or something.
I've got a PLC running everything, so I can do PID control and determine when it makes sense to turn on the boiler.
The hot water runs 140 on finish tank because there's a tempering valve on outlet. |
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engineer
Veteran Member
Posts:2749
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| 09 Jun 2009 12:53 AM |
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I favor sizing DSH buffer to match a full day's hot water use to deal with generation / use time shifts and to maximize recovery.
I favor sizing final tank to match worst hour's hot water use since standby losses are always cheaper than a divorce triggered by someone getting one or more cold showers...
That said I haven't thought through how solar impacts all of the above - would a strong marriage depend on fair weather?
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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joe.ami
Veteran Member
Posts:4377
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| 09 Jun 2009 07:03 AM |
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Okay well you got my thooughts on your "hypothetical" situation.
Just out of curiosity how much do you think this system will cost you.
Your 100 gallon tank with 2 double wall exchangers, two other tanks wiring and process piping should save you at least $300/yr (depending on # of people in home).
J
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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86turbodsl
New Member
Posts:45
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| 09 Jun 2009 08:47 AM |
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Well, I don't think the marriage would depend on solar input, since there's boiler backup.
As far as the system cost, that's irrelevant, since i already have all the tanks. It helps on cost that I'm a DIY type.
The Steibel Eltron dual coil tank was about 1K. The other water heater was already on hand as a spare.
I figure once I have the solar up, I should be looking at a 5 year payback or so. I found evacuated tubes for less than 1K.
I think of the solar as being a backup that runs when other stuff doesn't. In our climate, the solar would be really useful from April to October, and the DSH from Sept to March.
There's about 2-3 months of the year when we have the AC running and the solar would be good too. Pool heating someday? Who knows.
I guess my main goal here was to bounce the three tank idea off someone else and see if I missed something. With the current setup, the DSH sees 140F water from the finishing tank and it doesn't give much back to the tank at that temp. |
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joe.ami
Veteran Member
Posts:4377
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| 09 Jun 2009 08:01 PM |
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Posted By 86turbodsl on 06/09/2009 8:47 AM
Well, I don't think the marriage would depend on solar input, since there's boiler backup.
As far as the system cost, that's irrelevant, since i already have all the tanks. It helps on cost that I'm a DIY type.
The Steibel Eltron dual coil tank was about 1K.
-is this a code required dual, double wall heat exchanger?
The other water heater was already on hand as a spare.
I figure once I have the solar up, I should be looking at a 5 year payback or so. I found evacuated tubes for less than 1K.
I think of the solar as being a backup that runs when other stuff doesn't. In our climate, the solar would be really useful from April to October, and the DSH from Sept to March.
There's about 2-3 months of the year when we have the AC running and the solar would be good too. Pool heating someday? Who knows.
I guess my main goal here was to bounce the three tank idea off someone else and see if I missed something. With the current setup, the DSH sees 140F water from the finishing tank and it doesn't give much back to the tank at that temp. Ok, you missed nothing, you can spend thousands to get hot water for hundreds/yr (the fact that you have already purchased components does not make them free). Of course you could spend hundreds to get DHW for hundreds/year. But you were not interested in cost effective. You wanted support for your idea. Sorry, wouldn't encourage it elsewhere. In fact that is a common discussion with folks who distrust geo.....what if it fails? Well what if your furnace fails? You have quadruple redundancy....really, what for? "Savings?" I think not. Don't mean to sound negative by why ask opinions if only to "poo-poo" them? 'Course I'm just a simple mechanic. Wish you luck, Joe |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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86turbodsl
New Member
Posts:45
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| 09 Jun 2009 08:17 PM |
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Joe, not trying to poo poo you or your comments. I value them. I don't distrust geo, in fact, I speced it for this house.
I don't have enough capacity on the heat pump to get all my hot water needs. I live in Michigan and solar is sorta spotty here
due to cloud cover. So I need another source. Boiler is already there as it's my backup. I don't have strip heaters for backup heat
on the geo. House is all hydronic. As I see it, with the last tank being a simple electric water heater, I can either turn off the electric
and pray that it doesn't cool before it gets used, or leave it on, or remove it from the system. I already have the components because
it's what my HVAC guy put in and I'm trying to fix all the stuff he left me with. Like desuperheater without a buffer tank.
I can't very well take my stuff back to the store since it's already been used once. So I'm making applesauce from the rotten apples I got... :)
Now that I have your attention -
What would YOU do in this situation? |
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joe.ami
Veteran Member
Posts:4377
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| 10 Jun 2009 05:26 AM |
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You already have the solar?
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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86turbodsl
New Member
Posts:45
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| 10 Jun 2009 11:07 AM |
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I have everything but the evacuated tubes. |
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joe.ami
Veteran Member
Posts:4377
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| 11 Jun 2009 08:38 AM |
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I'm not a fan of using a boiler for DMH (most expensive appliance to do the job of the least). Gas and electric water heaters are cheap, use either to finish. I'd put DSH and solar together in upstream tank. Might circulate it as well to take advantage of extra.
Gets rid of a third tank and the "extra" redundancy (isn't that redundant).
j |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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86turbodsl
New Member
Posts:45
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| 11 Jun 2009 01:57 PM |
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Gas water heaters are very inefficient, and have high standby losses (chimney effect). electric I agree with you.
I don't think DSH and solar in same tank makes sense, because if the solar is working, the DSH sees high temp water
back to the heat pump, and that kills any effect it might have. I'd have to turn off the DSH pump maybe?
Do an either/or situation where the DSH runs or the solar runs, but not both? That seems like it might work.
I need to think that out a bit more. |
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engineer
Veteran Member
Posts:2749
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| 11 Jun 2009 09:11 PM |
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Joe said "I'd put DSH and solar together in upstream tank. "
I second the motion. If the DSH sees 140 deg inlet water because the solar is having a good day, so what? The finishing tank gets 140 water and doesn't need to run, which is the objective of an upstream tank. The superheat not then needed to heat water can add to house heat in winter or be rejected underground in summer.
I'm an engineer relatively unafraid of complexity in pursuit of savings (or just to satisfy curiosity) but I don't see a good case for a 3rd tank outside of a high demand commercial application.
(Let's see.. maybe you could have separate tanks for DSH and solar and a temperature switch-driven solenoid valve that switches the finishing tank inlet to which of the two upstream tank offers the higher outlet temperature at any given time...would need a differential control to keep it from flipping back and forth too often...) |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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joe.ami
Veteran Member
Posts:4377
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| 11 Jun 2009 09:20 PM |
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I still maintain "estra redundancy" is redundant.
j |
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Joe Hardin
www.amicontracting.com
We Dig Comfort!
www.doityourselfgeothermal.com
Dig Your Own Comfort! |
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86turbodsl
New Member
Posts:45
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| 12 Jun 2009 06:20 AM |
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Ok, that makes sense. Rejecting heat underground in summer would help winter for a while too I think.
I'm also an engineer unafraid of complexity. Heck my controls for this thing is a PLC with software I wrote.
But at the same time I don't want to take up room in the mechanical room for no benefit.
I'm just a little worried that when wifey draws a 100 gallon bath I run out of the cheap hot water. I can see her doing that
a couple times a week. That'll get expensive if I'm dumping millions of Btu's of propane at it every time. I've got reasonable confidence
that the DSH only runs 1/2 the year as our heating season runs about Oct-Mar/April. We still haven't turned the pump to AC this year.
So I get a couple months out of it maybe? Maybe I'll just run the storage tank at 200F. That should store a bit more heat. It's got pretty good
insulation. 3" closed cell foam.
Thanks for the advice guys. Makes sense to me. |
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engineer
Veteran Member
Posts:2749
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| 12 Jun 2009 08:02 PM |
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Some geo HP desupers won't operate if the water to them exceeds a safe limit, such as 130. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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86turbodsl
New Member
Posts:45
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| 12 Jun 2009 08:15 PM |
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I do believe there's a high limit switch on the pump in the HP. You are correct sir. I don't know the cutout temp though. |
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engineer
Veteran Member
Posts:2749
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| 12 Jun 2009 08:21 PM |
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If you are committed to a 3 tank setup to avoid burning propane during 100 gallon hot water draw events then I think I'd stick with your original plan of sequencing the tanks DSH, Solar, finishing.
Whether it is worth the cost and complexity depends on the frequency of 100 gallon draws. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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86turbodsl
New Member
Posts:45
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| 12 Jun 2009 08:31 PM |
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Yeah, I fear that's not something I could really figure out without some sort of data analysis of BTU's used and usage patterns.
I have the tank, I may do it I don't know. I need to crunch some more numbers first. |
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engineer
Veteran Member
Posts:2749
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| 12 Jun 2009 09:14 PM |
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Nothing compares with actual data.
To that end I mounted cheap digital hourmeters on the geo and the water heater (Reddingtons - $30, very flexible - same part number works off 24 Vac HVAC control power or 240 Vac line power and anything in between), and now have a years worth of data correlating hot water and HVAC cost vs weather. Basically every dollar I spend on heating and cooling returns 50 cents in avoided water heating costs via the desperheater plumbed into its own 80 gallon buffer tank.
Right now we are in an early summer heat wave with highs in mid 90s, so geo is running 12+ hours per day costing about $2, but I get 160 gallons of hot water ready for use at near zero cost.
I also restrict the open loop flow so as to dump 90 deg water into a 600 gallon kiddie pool that my 2 and 4 ear old play in for an hour before bed - the fatigue that induces is priceless. |
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Curt Kinder <br><br>
The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>
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