Conflict over Heat source.

L'town Radiant_2

I have sized and designed a small radiant renovation for a home owner who is set on using his domestic water heater as the heat source for the system. The heating load is approximately 15,000 BTU/h and total system flow would be 3.5 GPM. What kind of performance\issues can I expect out of using a standard 40gal/40,000 BTU/h gas fired water heater paired with a brazed plate heat exchanger...anything I should look out for?

I have attached a drawing of my proposed system.

Thanks in advance for everyone's help.

L'town Radiant_2

missing attachment....

seem to be having trouble attaching my drawing!!!

nicholas bonham-carter

DHW/hydronic running costs

if i were the customer, i would ask: will it cost more to heat this way, and would i be more likely to run out of hot water.

when you have to buy a pump, and a strainer, and a heat exchanger, is there any saving???--nbc

cattledog

temperature control

One possible problem with systems like this is temperature control of the water in the radiant loops. Typically, the water heater will have a fairly large on/off differential around its set point. Then, there is a fixed flow rate through the water heater side of the HX, and its not clear what the output temperatures on the radiant side will be given the different flow rates.



Your drawing is pretty precise and shows different temperatures and flow rates in the loops. I guess the question is how well the system will perform as loop temperatures vary around the values of your design. It is not clear that the low temperature loop (95F) can be achieved without some sort of mixing or bypass.

L'town Radiant_2

yep!

Good points! I appreciate the feed back. I certainly did forget to add the mixing to the system to obtain proper loop temperatures...guess that's what happens when you re-edit an old drawing from other jobs! 

To people who do this enough, it is clear that using a residential domestic water heater is not the way to go. The trouble for me was in explaining just why.

Thanks again for everyone's input!

Unknown

I did a system

I did a system almost the same as this with water heater and plate exchagner, etc.. However, its a one zone system and I installed manual by_pass valve.. That was in 1999... customer have no complain except with ghost heat flow and over heating, til I put extra flo stop check valve in supply side.. Now I'm back there work on main house with new addition, re route radiators and plumbing, etc

Unknown

I did a system

I did a system almost the same as this with water heater and plate exchagner, etc.. However, its a one zone system and I installed manual by_pass valve.. That was in 1999... customer have no complain except with ghost heat flow and over heating, til I put extra flo stop check valve in supply side.. Now I'm back there work on main house with new addition, re route radiators and plumbing, etc

Charlie from wmass

They do make water heaters with built in heat exchangers.

They could get a new heater and a heat exchanger in a unit designed to do as you want and you will save a pump. [url=http://www.bradfordwhite.com/images/shared/pdfs/specsheets/549-B_ICON.pdf]http://www.bradfordwhite.com/images/shared/pdfs/specsheets/549-B_ICON.pdf

SpeyFitter

I know times are tough but...

If a homeowner was absolutely hell bent on you having to install a system like this I would run, far, far away.

Hot water tanks are not built as robustly as a boiler and subsequently do not carry an ASME stamp (at least as a Boiler anyways). I know it's a small heating load, but you'd come out light years ahead with a small electric boiler, which after factoring in the costs of gas versus electricity, would probably be on par to trying to use an inefficient gas tank to heat through a heat exchanger with 2 pumps versus 1.  And the electric boiler would have one small pump, and would be reliable, simple, and no fuss.

I took out a 3 year old Bradford White Combi Gas Hot water tank a year and a half ago. It was set at 180 degrees mixed down with a thermal mixing valve and they used the heat exchanger portion of it to heat about a 1000 square foot basement radiant floor zone. The tank went prematurely obviously, and it was a contractors who we did work fors sisters house. The other plumbers they use did the install said that was the only way to get any output out of it. So I guess if you dont' mind spending big $$$ to re & re a combi tank every few years, irregardless of the fact the tank might be covered by warranty, go for it.

Personally, hot water tanks have a purpose, and boilers and heat pumps have a purpose. Pick the right tool for the job.

EricAune

Why not an RMB?

Have you considered a Taco RMB?  Variation of temps on the heater side become less of a factor given it will also operate on ODR.  The basic concept is variable injection mixing.  You will still be able to have multiple temps on the radiant side.



I have used these for small loads when an additional appliance wasn't necessary or not an option.  No complaints here, in fact I would prefer it.  Both pumps and exchangers in one package.



Consider installing a thermostatic mixing valve on the domestic to boost the effective storage volume and offset any load the RMB would be placing on the heater.

NRT_Rob

this is not a big deal.

the water heater will run about 75% to 80% efficient in a heating app. Not that bad. Much better than the "EF" would indicate. though you are reducing your DHW performance as well, so you better make sure the tank can do both at once.



Use an injection mixing control on the heat exchanger. cheap upgrade there.



why check valves on your zone valve loops? that's pretty unnecessary.



the only thing I've ever seen bite anyone here is either bad HE sizing, or if the sensor on the tank is in the wrong spot you can get a runaway tank demand. with injection mixing, water back to the tank can be as low as room temp, huge dT, and if it passes the sensor on the way back into the tank, it fires. and fires. and fires.



I've only seen that once. So ideally you'd use a unit with separate taps, but we do what we must.



a Taco X-block works too, though we having some problems troubleshooting one right now generally it makes the install pretty simple if the system pump in the unit will do the job, which it should if the water heater will. I prefer separate and standard components (two pumps anyone would have on a truck, a 356 which is the most common controller in the world, and a plate HE... pretty easy to service).

NRT_Rob

Scott

you're judging the whole class by a bad install. You can trade horror stories about every heat source in existence, but just because people don't know how to size DHW tanks and heating appliances doesn't mean they can't, and don't, work.



they can work. and they do. But with all things, if you don't know what you're doing, then you can get burned. which is why reputable people do things like L'Town here did, and try to get info before they do something new.

DavidK_2

I think this is key

You will be removing nearly 1/2 of the DHW heating capacity. The first cold morning when everybody wants to take a hot shower, and then step into a warm room, they might not be so happy with their decision (after stepping out of a cold shower, into a cold room).

L'town Radiant_2

Hmmm,

That's a good thought Eric, but if they won't swing for the price of a small electric boiler I doubt they'll go for the mixing block.

L'town Radiant_2

Here ya go.

Ok folks, I'm sticking to my guns and saying its a small electric boiler or nothin! Here's the revised drawing. Thanks for everyone's input!

....I might have to start posting all my drawings on here!...

Brstr

Replace zone valves

You will need to remove the two zone valves in the mixed temp zones and replace with pumps sized to the friction loss and gallonage of the load on that zone.

NRT_Rob

hmm.

2 mixing valves, 3 pumps, electric instead of gas.



unless your electricity is cheap, I think they would be better off with the tank heater and an injection mixing control through the HE. both now, and later.



if electricity is cheap, then go nuts, but what's with all the mixing valves, do you really need 3 temps? this would be a really nice place to use an ECM pump and zone valves... no minimum flow requirements for most electric boilers.

Mark Eatherton

Allow me to disagree Rob...

I understand where you are coming from, with the EF, and AFUE and all, but having actually lived with one of these in my basement for about 4 years, I think you are giving it more credit than it deserves..



My "cheapo heat source" was a conventional 40 gallon, 40 K btuH water heater, except that I found and installed a normally closed solenoid rated for use with natural gas. I cut that valve into the 1/2" OD tube that goes from the snap acting gas valve down to the burner. Bear in mind this was pre FVIR requirements, so am not even sure it can be done now... In any case, in my best effort to make the piece of crap water heater as efficient as I could, I put a tekmar ODR controller on it and set it for full range operation (start @ 70 deg. supply at 65 deg. OSA, and end at 140 deg. F when OSA = 0 WWSD = 65 degrees F)



I use to sit in my office, and hear that darned thing turn on and run, and run, and run... Even when it was only tepid (like, around 50 degrees F) outside. IT LIKED TO HAVE DROVE ME NUTS!!! I keep thinking, Why the heck is that piece of crap running?



I finally got tired of listening to it run and got a mod con boiler dropped in its place. And then THAT boiler ran forever, and I kept thinking to myself, "The wife is going to KILL me when she gets the utility bill...." When the reaper finally came (utility bill) she said it was the lowest gas bill we'd ever gotten for that period of time (dead of winter). It reduced the energy consumption by around 40% over what the tank style heater had done.



To the original poster, if you really want to give these people a pleasurable radiant experience, maybe you should consider going with an electric radiant floor system for this small app. The installed cost is less, the reaction time is less, and the comfort levels are the same. And if you use a low volt system, you are qualified to perform the installation. Look at STEP Warm Floor for a good system. And it IS 100 % efficient...



That is just my personal experience that I thought you might want to hear.



HTH



ME

L'town Radiant_2

Cheap Power

Yep,  the power is cheap. Job is in eastern Kentucky, the coal for the local coal-fired power plant is literally in the backyard. I'm just waiting for the guy to ask me how he can use the waste heat off of his still to heat the house!

NRT_Rob

You're always allowed to disagree

but a couple of things.



1. I would never claim that a water heater was in the same league as a mod/con boiler. Jumping from the 75-80 to the 95+ range, plus going from atmospheric to sealed combustion, results in real savings. It's just that, if your heat load is low enough, even those savings may never be economically justified. Ever. at 15kBTU max loads, unless the client is in alaska or a severely cold climate with lots of degree days, he's probably in the boat of "hey, a modcon would be nice, but it will never pay back". and it also would not run at 95% efficiency when it would be below min mod all year.



an electric heat source might be "100%" efficient, but very few locales would find operating an electric boiler on part with a 75% to 80% efficient tank heater. Even at 60% gas will run circles around electric in many locales. but that depends on local fuel rates. Same deal for electric mats... for very small areas or very low loads, maybe. but at 15kBTUs/hr, I doubt this area is one of them.



2. You hacked that water heater to do nothing it was ever built to do. I am not assured that adding a reset control to the tank heater was a good choice and I would not assume that it was operating well.



3. It's not hard to beat a home cheapo special. A basic sealed combustion water heater is still inexpensive and would negate a lot of the differential between an atmospheric unit and a sealed combustion mod/con.

NRT_Rob

If electricity is cheap

then why did they want a gas water heater in the first place?

L'town Radiant_2

I never

Assume that customers are reasonable people. Just people that I'll need to reason with.

BobbyG

L'town - hoosier counterpart

L'town,

I bet you been sippin the bourbon contemplating this conundrum....

Your hoosier counterpart has had the same customer profile and obliged customer with Heat Exchanger (much like your second drawing) and after several years I can tell you they were not happy with it.  The customer was a residential plumber.  When I asked him about it.  He said his wife yells at him everytime she runs out of hot water! haha

I would use those tankless heater isolation/drain valves for easy maintenance to descale the heat exchanger on the dhw side.

Happy hydronicing!

Bobbyg

Mark Eatherton

HACKED!?!?!?!?!

I BEG your pardon, I used tubing cutters, NOT a hack saw :-)



In response to your response to my response...



1. I didn't think you were thinking I was thinking about comparing the two. I am just trying to demonstrate what an energy hog tank type water heaters are.



2. The water heater is made to heat water, no? I was simply changing the temperature BELOW the set point of the heaters snap acting safety/limit/operating control, and operating a pump based on WWSD. If anything, it would have increased the seasonal performance by reducing the standby losses, making it as "efficient" as it could be. Nothing more, nothing less, and nothing really in violation of the code or the safety factors built into the device in the first place. I couldn't make the heater go hotter than the snap acting aqua stat would allow it to go, and it was a dedicated, space heat use only, "approved" appliance.



It was like having a slipping clutch in an old pickup truck trying to climb a hill with a heavy load....



3. Read my tag line...



Thanks for agreeing to disagree with me in a constructive and educational way ;-)



ME

SpeyFitter

Electric Boiler

Instead of 3 pumps, put 1 pump and 3 zone valves. Make that Pump a Grundfos Alpha. One grundfos alpha should easily be cheaper than the 3 pumps you have listed, plus it's more efficient, and will negate needing a pressure differential bypass. Also makes for slightly simpler wiring.  Most electric boiler (Thermolec/Argo as examples) should have enough "ability" to control this set up with one pump, plus some electric boilers have outdoor resets as well.

L'town Radiant_2

Thanks BobbyG

You know me all too well....glad you didn't notice the Woodford Reserve stain on my piping drawing! ....That's a real good idea about the tankless heater valves, I'll have to keep that in mind.

Scott K: If I were to change the set up to how you suggest I would lose the ability to operate 3 different temperatures. Each zone is a different type of installation, 1 is a tubing hung in the joist bays, 1 is in a gypcrete over-pour, and 1 is in a aluminum floor tracking system. I might be able too get away with sending the same water temp to the gypcrete and the floor tracking, but the joist tubing will definitely need a higher temperature than would be safe for the other two zones.....that's my thinking anyway, sound right to you?

scott markle_2

DHW for heat

There is I think a bit of a knee jerk reaction against using tank DHW heaters in combined heating applications. Maybe we are just frustrated by having to explain (again) why the affordable open system being peddled by an internet vendor in vermont is not a good idea. I would think that a budget that includes extruded plates and Gypcreet might also include some resources for an efficient and environmentally sound heat source. The electric option may make economic sense in your location, but does it make common sense?Your cheap coal fired electricity is My acid rain, mercury fallout, and anthropogenic climate change. Why burn a dirty fuel to create thermal energy, convert it to mechanical/electrical energy (at a 60% loss) only to turn it back into thermal energy through resistance coil. Also consider this: The future "cheapness" of coal fired electricity is not a certainty. At some point in the near future (hopefully) we may be forced to pay the real costs of this energy source. If we want a decent future for our children, we can only hope these sort of actions happen soon.Here is a picture of a panel I built for a HTP Phoenix water heater and a 20K radiant slab. I hate cycling and I had concerns about how a small low temperature load like this would perform with a mod-con. Ultimately I think that the cost (even with the Tekmar injection mix control and Alpha circ.) was similar to what a boiler and indirect . Plus I get DHW production efficiency in the mid 90's year round without the losses of a boiler and indirect.

scott markle_2

DHW HX

I chose to build my own HX pump assembly over the Tako all in one device because I wanted to keep my tank temperatures at 120( high condensing efficiency). The Tako has a relatively small HX and requires a fairly significant Delta to achieve it's rated transfer capacity. Upsizing the HX ensures that the tank can stay in the condensing temp range.

scott markle_2

jpg issue

Dan,



The issue is on my side, I used the grab tool to crop the selection and for some reason this made the file unreadable to other applications. Thanks.

NRT_Rob

there are a lot of variables there mark

enough that I am not going to concede that a hacked water heater is a good demonstration project. if you wanted to log it "pristine" and then "hacked" then I would be happy with the anecdote. but variability in stratification, turbulence, sensor positions... well, I couldn't sort through it all!



I would buy 20% to 30% difference in the end from top end (mod/con) to bottom end (home cheapo atmostpheric) though, sure. but for the heaters most people are enlisting for heating I would estimate 2/3rd or 1/2 of that differential, and it never pays ignore the context of the overall heat load that is being serviced.

NRT_Rob

exactly

so reason with them

NRT_Rob

?

how does the phoenix avoid the standby losses of an indirect and boiler?



it has a flue... like a boiler.. and a jacket... like an indirect.



it's a fine heat source, I'm not arguing that, I just think you're overselling a bit there. Generally I'd prefer a mod/con anyway, so I can run it right down to 80 degrees or so, but for high rate DHW systems it's a good choice.



and I could probably play "greener than you" all day long... but at the end of the day it's not my job to make my clients live the way I think they should. I provide information so clients can make informed decisions and I try to provide an appropriate context. Since I do not know the future of energy, I will refrain from telling my clients what it is, and while you type here (on your electricity using computer, with its toxic onboard electronics) about mercury, remember that your house too is made of glass.. so let's not get too high and mighty about burning a fossil fuel in preference to... burning a fossil fuel. gas may burn cleaner, but it's not exactly green.



with hydronics, they can always change, that's the main beauty of hydronics in my mind. It doesn't care what heated the water. so if electricity makes sense for a person, fine. when it doesn't, fine. ready for air to water cold climate heat pumps? fine. PV solar to electric? great. whatever. we're just circulating here...

Mark Eatherton

Life is nothing but a bunch of variables...

And trust me, I had total control over the variables on this project.



I made my point. An energy hog, even with lip stick on it, is still an energy hog. Plain and simple.



Efficiency wise, it don't get much worse than this :-)



But, that is what makes this a great country. If you or anyone else wants to use it as a heat source, it is your option. It's your money, burn it wisely. :-)



ME

EricAune

Cost evaulation, time & labor

I realize the cost of the RMB is high, compare it to the cost of the components needed to pipe in a HX.  Two pumps, strainers, relays and a whole bunch of man hours.



Figure the potential energy saved by using ODR and variable mixing.  I bet if you compare the two methods you the cost will be close, I think the RMB has features that blow the plate exchanger out of the water.

NRT_Rob

that's just it mark

you are burning the extra money on the mod/con, if you put it in on a system it is wildly oversized for in the first place, with a small enough heat load to make whatever additional efficiency you DO get moot.



Hyperbole aside, the name of the game is not always the most efficient heat source you can afford. You could put a Vitodens and Vitocell tank on a kitchen sink. But that would obviously make no sense at all. Likewise, putting it on a tiny heat load wouldn't make much sense either.



it's about using the right tool for the job. I don't think you were testing your heater in a 15kBTU max load scenario, were you? It's not a direct vent unit, was it? If both of those things were true, I think you'd be singing a different tune here. Just doing the Math would illustrate why. Of course your HDD there in CO can easily be double what most of the country sees too. remember that, when you finish the math.



knock ten percent off your differential, cut your load in half (guess) and cut the heating degree days in half (guess) and you're talking about something much more like the scenario most people would be in at a 15kBTU load in a moderate climate, like new york/PA. Suddenly that 20%. is a lot less money.



Double the load, double the HDD, and compare to an even cheaper water heater, and of course it makes no sense at all.



This is why anecdote is no substitute for math

scott markle_2

Reply to Rob

Sorry for the preachy tone of my earlier post.

Sure I'v got an issue with electrical resistance for heating. We spend a lot of time here talking about efficiency. The politics of carbon (and coal use) will, one way or another, shape our future. I think it's fair game to call into question the sensibility of electrical resistance as a primary heat source, especially in light of the talks in Copenhagen.

Are you saying that one who benefits from the comfort and convenience of modern life should refrain from critiquing it's path? It's my guess that my digital indulgences would be fully offset, if one person should chose not to use electrical resistance as a result of my ranting.

As far the efficiency of an indirect and boiler Vs. an appliance like the Phoenix. In my observations most mod cons don't do much condensing while servicing indirects which (often) have undersized heat exchangers. Second a boiler indirect pairing strands heat in the boiler at every cycle, this a significant loss for cast iron boilers in summer operation, and I suspect not entirely insignificant, even for low mass boilers.

The Phoenix will crank out 120 degree water while solidly in the condensing range, and any residual heat from the burner is transmitted to the water instead of sitting in the boiler and pipe work. The other part of this is cycling. In my experience a mod con serving a low BTU load @ 80 degrees is going to short cycle. How much is the advantage of operating at 80 as opposed to 120 eroded by chronic cycling?

I'm not playing greener than thou, just looking for spirited on topic debate.

NRT_Rob

all the stranded DHW temp in the world

on a low mass boiler with post purge is blown out of the water if I can run the mod/con 1% or 2% more efficiently on a real heat load. Control cycling all you like. I like the phoenix, but I will choose a mod/con, indirect, and perhaps a small buffer tank any day of the week on most systems unless the DHW demand is huge. and I'm quite confident I can beat the 92% efficiency it lists at typical radiant return temps. My mod/con at home runs 90% on DHW calls. If I lose 2% to 4% on DHW and gain it back on heating... I win.



As for electricity I'm saying you do not know the facts on the ground to make blanket statements about heat sources. Coal stinks, sure, but up here in maine for example we don't use coal for electricity, we use oil and natural gas primarily. and I send all my money to a company that generates only hydro and wind.



But that's not the point either. The point is, it doesn't matter what carbon politics are "going" to do. when they do them, hydronics can adapt. an electric boiler is a pretty cheap heat source to abandon later if another fuel/energy source makes more sense. So you don't have to predict the future or the copenhagen talks with hydronic heating. You can plan for now and adapt to whatever happens later. Speculating about the future is just speculation... it's fine, but it's not responsible to force your clients to plan around YOUR speculation.



Two years ago, would you have said natural gas will probably stay flat in price unless/until we transition a lot more energy usage to it than we currently have? I wouldn't have. But that's the boat we're in. Go figure, huh? I'm not arguing for personal complacency, I just advise treading lightly before taking others along for the ride. Make the points you have to make, but I wouldn't judge anyone for disagreeing with me. And I don't see many of us boycotting electricity either.



I'm about to install an air to water heat pump I expect to run at a COP of 3. But it's still electricity. On a low load system, with my money going to clean energy people even though some more oil or gas will definitely be burnt with daytime peak loads elevating because of my load. Is that Green?



If so, then why not an electric heater on a third of the load?

If not, Then given I have done all I can reasonably do on heat load already, what would be greener and why?

scott markle_2

Phoenix efficiency

The HTP graph that illustrates efficiency @ different return temperature and modulation is not indexed in a way that is very precise. Still my reading of this graph would indicate an efficiency much closer to 95% than 92% (at mid level modulation.) Judging from the copious condensation my intuition tells me this thing is humming along very well. In comparing heating and DHW efficiency remember that in a low load structure DHW could account for a third of the overall BTU requirements.



A buffer tank, indirect and boiler occupy considerably more floor space than the Phoenix alone. The Phoenix will also do 85ft. (combined) venting through a 2'' pvc pipe. It's not right for every job, I'm not going to stop using boilers, but I think there are some compelling reasons to give this approach some serous consideration in certain applications. Hey, throw me a bone, the panel looks nice doesn't it?



Not quite getting your point on the electricity issue, or the swappable hydronic heat source thing. Electric resistance could care less about operating temperatures or cycling a condensing combustion device or heat pump needs more finesse to achieve it's rated efficiency. Why even bother with Hydronics , cheap base units will do the trick. This gets back to my original point, if your going to design an effective low temperature hydronic distribution system with all of the associated costs why stop at the heat source. In my opinion it's better to skip the fancy floor heat and do oversized base or panel rads. and put the money into a environmentally sound power plant.



How you can argue with the fact that electrical resistance is inherently wasteful, Burn something,waste 60% of that heat converting to electricity then turn it back to heat at another location, does this really sound like a good idea, It's another case of externalizing costs, can we afford to continue ignoring the externalities?



BTW- Who makes the air to water unit your using?