Need help w/decision on DHW heater.  Have only electricity.  New house in Michigan, 2,400 sq.ft., well insulated, walkout ranch, geothermal 5-ton water-to-water, radiant infloor heat, desuperheater.

What kind of water heater?  Plumber says we need 80 gallons.

Is there a reason for maybe splitting it into 2 tanks?  Does solar water heater make sense to work w/desuperheater (but what about the many cloudy days in MI?)  High-efficiency water heater (what is it?), hybrid water heater (what is it?)

I'm confused.  Some advice, please.  THANK YOU!

Thanks, we need more people building new houses in MI.

This system uses one tank and supplies all his hot water from geo. Hard to beat that price.

http://www.ourcoolhouse.com/monitor/monitor.htm

What type of water heater is it?  Our HVAC contractor is ordering equipment tomorrow morning.  The desuperheater will not be working all the time (when the geo isn't working "full speed"), so as I understand it, we need to still buy a DHW tank/water heater to tie into the geo system.  I checked out the website, but I'm not sure what it is.  Please clarify.  Thanks so much.

Unfortunately, I don't know more about his setup than what is on the web site.

Solar Water heater would definitely make sense as you have requirement for huge amount of water.Initial cost would be high but you will get benefit in the long run.

Posted By cbfriend on 05 Dec 2010 11:27 AM
Need help w/decision on DHW heater.  Have only electricity.  New house in Michigan, 2,400 sq.ft., well insulated, walkout ranch, geothermal 5-ton water-to-water, radiant infloor heat, desuperheater.

What kind of water heater?  Plumber says we need 80 gallons.

Is there a reason for maybe splitting it into 2 tanks?  Does solar water heater make sense to work w/desuperheater (but what about the many cloudy days in MI?)  High-efficiency water heater (what is it?), hybrid water heater (what is it?)

I'm confused.  Some advice, please.  THANK YOU!

There have been a couple posts about drainwater heat recovery systems - something like that may allow you to use something smaller than an 80 gal...

Posted By jerkylips on 10 Dec 2010 11:19 AM

Posted By cbfriend on 05 Dec 2010 11:27 AM
Need help w/decision on DHW heater.  Have only electricity.  New house in Michigan, 2,400 sq.ft., well insulated, walkout ranch, geothermal 5-ton water-to-water, radiant infloor heat, desuperheater.

What kind of water heater?  Plumber says we need 80 gallons.

Is there a reason for maybe splitting it into 2 tanks?  Does solar water heater make sense to work w/desuperheater (but what about the many cloudy days in MI?)  High-efficiency water heater (what is it?), hybrid water heater (what is it?)

I'm confused.  Some advice, please.  THANK YOU!

There have been a couple posts about drainwater heat recovery systems - something like that may allow you to use something smaller than an 80 gal...

If the house is going on an acreage with a septic tank, I would not use a drainwater recover system. The septic tank needs all the heat it can get to operate efficiently.

Posted By FBBP on 11 Dec 2010 01:45 PM

If the house is going on an acreage with a septic tank, I would not use a drainwater recover system. The septic tank needs all the heat it can get to operate efficiently.

Not surprisingly,  manufacturers of drainwater heat recovery systems beg to differ:

http://www.retherm.com/ReThermFAQ.htm  (See item #6)

I've read in several places that with anerobic digestion in septic tanks it's not an "all the heat you can get" that optimizes it, but rather keeping it between 50-60F or some similar range.  It's highly unlikely that most drainwater heat recovery systems will be so effective that the out it dropping much below 50F and cooling the tank, even with 35F incoming water.  With a pretty good heat exchanger installed you'll be getting something like a 25-27F rise in temp on the incoming water flow, and a similar reduction in temp on the drain water flow. The drain water is starting out at ~100F or slightly above at the floor of the shower, so figure it's still about 70-73F  on it's way out.  It would probably take an (insulated) heat exchanger 3 stories tall to get the exit temps down to 2F above the incoming water temp and thus actively chilling the septic tank.

I would think the soil temp surrounding the tank has a much bigger effect on it's operating temp than the temp of the water you're dumping in, since in most homes there would be many hours between significant slugs of warmer water hitting the tank.  Even if you're dumping 60 gallons (several showers worth) of 100F water vs 70F water into a 1000 gallon 50F septic tank surrounded by 50F dirt every day, the effect on the tank temp from that discharge is minimal, but may be measurable in the very short term.  But 10 hours after the fact, probably not- the tank will have settled to the soil temp. If you insulate the hell out of the tank you might see a difference over time, but would the difference be enough to really matter in an uninsulated tank? Probably not. (But if there's been a carefully constructed experimental measurements of those effects that indicates otherwise I'd really like to see them!)

Be sure the desuperheater has its own buffer tank. Downstream of that a conventional 80 gal storage tank water heater probably makes the most sense economically. The desuper should meet about half your hot water needs at very low cost. That means ROI on an expensive solution (Solar, Heat Pump Water Heater, drainwater heat recovery, etc.) may be quite long.

I agree with Dana's opinion and analysis of a minimal impact of drainwater heat recovery on a septic tank. If I lived up north with chilly incoming water and had a suitable vertical length of main drain line, I'd look hard at a Retherm

Solar water heaters are an excellent choice. However, the logistics of a solar scary compared to a typical device configuration.

Posted By engineer on 16 Dec 2010 07:07 PM
Be sure the desuperheater has its own buffer tank. Downstream of that a conventional 80 gal storage tank water heater probably makes the most sense economically. The desuper should meet about half your hot water needs at very low cost. That means ROI on an expensive solution (Solar, Heat Pump Water Heater, drainwater heat recovery, etc.) may be quite long.

I agree with Dana's opinion and analysis of a minimal impact of drainwater heat recovery on a septic tank. If I lived up north with chilly incoming water and had a suitable vertical length of main drain line, I'd look hard at a Retherm

Retherm is just one of several vendors, and there is a real range of price/performance- they're not all made equal, even if they're all pretty-good. 

At least consider Natural Resources Canada's comparative measured-performance numbers before plunking down hard cash:

http://oee.nrcan.gc.ca/residential/...cfm?attr=4

These numbers compare apples-to-apples at 2.5gpm shower flows.  The actual return in percent will be higher at lower flow rates, the return in BTU/hour and total BTUs would be higher at higher flow rates, but the % fraction would be lower. (A 50% version measured at 2.5gpm  may only return 40% at 7.5gpm, but it's a bigger number. It would also be returning closer to 55% at 2gpm, and even more at 1.5gpm.)

Look also at which models/vendor do and don't qualify for subsidy by your utility or state, eg:

http://www.mnpower.com/powerofone/o...gunits.htm

http://egov.oregon.gov/ENERGY/C...trec.shtml

It's also worth digging out the pressure drop with flow-rates, which also varies considerably by manufacturer & model. This is where Renewability's designs were beating the competition soundly a few years ago, particularly on taller units, something they like to crow about:

http://www.renewability.com/uploads/documents/en/backgrounder.pdf

I"m not sure what the state of the art is this week but it's a moving target- they've all been improving over time both on efficiency & flow, and are quite competitive despite (or because of?) a relatively small market to date. 

There's quite bit of background squabbling over everything from patent infringement to mis-labeling to perceived favoritism in government testing & modeling writeups- a regular tempest in a tea-pot when viewed from outside of this specialty-industry.  I try not to get sucked in, and tend to believe that the testing agencies try to do a good job, and that legal issues are better sorted out in court, since both Canada & USA are first-world countries with trade agreements in place, and have first-world judicial systems that can rightly weigh the evidence on any disagreements over intellectual property & labeling issues better than internet bloggery or forums like this one.  YMMV.

Posted By Dana1 on 15 Dec 2010 06:15 PM

Posted By FBBP on 11 Dec 2010 01:45 PM

If the house is going on an acreage with a septic tank, I would not use a drainwater recover system. The septic tank needs all the heat it can get to operate efficiently.

Not surprisingly,  manufacturers of drainwater heat recovery systems beg to differ:

http://www.retherm.com/ReThermFAQ.htm  (See item #6)

I've read in several places that with anerobic digestion in septic tanks it's not an "all the heat you can get" that optimizes it, but rather keeping it between 50-60F or some similar range.  It's highly unlikely that most drainwater heat recovery systems will be so effective that the out it dropping much below 50F and cooling the tank, even with 35F incoming water.  With a pretty good heat exchanger installed you'll be getting something like a 25-27F rise in temp on the incoming water flow, and a similar reduction in temp on the drain water flow. The drain water is starting out at ~100F or slightly above at the floor of the shower, so figure it's still about 70-73F  on it's way out.  It would probably take an (insulated) heat exchanger 3 stories tall to get the exit temps down to 2F above the incoming water temp and thus actively chilling the septic tank.

I would think the soil temp surrounding the tank has a much bigger effect on it's operating temp than the temp of the water you're dumping in, since in most homes there would be many hours between significant slugs of warmer water hitting the tank.  Even if you're dumping 60 gallons (several showers worth) of 100F water vs 70F water into a 1000 gallon 50F septic tank surrounded by 50F dirt every day, the effect on the tank temp from that discharge is minimal, but may be measurable in the very short term.  But 10 hours after the fact, probably not- the tank will have settled to the soil temp. If you insulate the hell out of the tank you might see a difference over time, but would the difference be enough to really matter in an uninsulated tank? Probably not. (But if there's been a carefully constructed experimental measurements of those effects that indicates otherwise I'd really like to see them!)

Some comments It is definitely not a case of all the the heat you can get. If you raised the temp. more than 5 or 6 degrees you would kill all my good little bugs and have to culture a new bunch for the new heat range. Not so different from a human digestive track after a fever. If you continue to shock the system, it will never have a stable population. Do the math. A showers worth of heat into a effluent chamber of about 750 gallons (imp.) will only raise the tank a small amount. But it is this small amount that we are after. The existing bugs that are almost dormant due to being at the lower end of their temp. range now get quite active. Their activity raises or keeps the temp slightly elevated for another period of time before they chill out again. In our area it is the difference of 42º to about 48 to 50. My farm clients very seldom need their tanks pumped. My DCF often need them pumped every year. The main difference is on the farm there is a constant addition for warm water through out the day. The people living on the acreages but working in town tend to use all there hot water in two bursts so the tanks swing wildly in temperature. It would seem to me that any money you save in recovered heat you will pay to the pumper truck, plus you have paid for the recovery unit. This is assuming you pump. If not you could ruin a $30,000 dollar investment to save a few dollars. Treat you septic system with respect and you will save a lot more money than any recovery unit will.

I DID the math, which basically say other factors are a much larger factor on the tank temp than the BTU delta of the heat recovery. If it's that sensitive to such modest changes in heat input, better care would need to be taken on how deep on the plumbing & tank is buried, and whether it needed to be insulated against ground temps vs earth-coupled, (or even heated) etc.

Those "wild" swings in temp of slugs of 20-60 gallons of 90-100F water into a 1000gallons of 50F tank doesn't amount to much- at most a degree or 3 or 4 (on the high volume high-temp end), whereas the depth of burial and moisture content of the soil above/surrounding the soil will make for seasonal differences of several degrees.

A 75gallon slug (~4 hot showers) of 100F water would temporarily raise a 50F 750 gallon tank a full 5 degrees, a shock you consider on the edge of damaging, which would be an argument FOR, not AGAINST drainwater heat recovery for those users- the more modest thermal input from the heat-recovery equipped shower would be only a couple of degrees, putting less stress on the bacterial cultures. If we're talking a single shower, the difference in temperature-bump to the 750gallon tank between heat-recovery/no-heat recovery is less than half a degree. There's a bump with both, but is the half-degree difference a make-it-or-break it deal? I'd need more than the theoretical to buy it- show me the data first. Septic systems seem to have a good track record over a wide range of water use patterns- includiing short vs. long showerers, tub bathers, etc. If short-changing the bump a half-degree on the shower draws are breaking it, it's already BEEN broken by those who take 5 minute showers vs. 10minute showers. If anything, drainwater heat recovery is babying the thing by limiting the temperature bumps from large shower draws to tolerable levels for the bacteria cultures.

Drainwater heat recovery has NO effect on water usage patterns- those who work in town will still have zero input during the day, and those who work the farm will have some very modest intermittent inputs of mostly 60-75F discharges, not 20 gallon slugs. Drainwater heat recovery has essentially NO measurable effect on the exit temp of toilet flushes or washer drains due to the temporal displacement between drain & draw- it's mostly a shower thing. (It's effect on short draws like hand washing is similarly un-measurable- the heat exchanger isn't even fully purged on the potable side on short draws, and the cooler incoming water would only reach the very bottom of the HX, if at all. The potable wrap stagnates to the temp of the room it's in, which is about the same temp as the outgoing water before it hit the drain.

Is washing your clothes in cold or warm water, rather than hot, or using a water-sipping washer going to break your septic biology as well? Are low-flush toilets robbing the tank of precious BTU inputs? Did mandated low-flow showerheads induce a pandemic of septic system failures? If yes, where's the evidence? (And if yes, why are local agencies in cool-water country recommending all of the above for septic tank users? eg: http://www.kingcounty.gov/healthservices/health/ehs/wastewater/owners/waterwise.aspx or http://www.co.kent.de.us/Departments/PublicWorks/documents/SepticTankBMP.pdf Seems reducing dilution volume & contamination are more important factors than the BTU contribution of the effluent by those recommendations.)

Solar water heaters-also called solar domestic hot water system-can be a cost-effective way to generate hot water for your home. They can be used in any climate,and the fuel they use-Sunshine-is free!

In northern climes solar heating is out and solar DHW has a dubious ROI providing 50% of your DHW, if perfectly installed.

You already have Geo so your installer should know the answer to output of your desuperheater as suggested. Many will need crude resistance backup but it isn't a perfect world.