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Tankless Water Heater For Floor Heat
- Thread starter 2Biz
- Start date
I think some of my pumps are over 20 years old! 
2Biz
Thread Killer!
Now that it has finally warmed up and everybody is starting to "Heal" from such a cold winter, I decided to post an update to the thread. In January and February, it seemed like my floor heat never turned off or the temps basically never got above 32°. So it pretty much had to heat the floors 24-7 for those 2 months. We had temps down to -16° more than one night and the demand heater kept up without changing any of the settings. It sort of automates itself the way I have it set to cycle depending on return glycol temps. I didn't even have weep water freeze on the floors at those low temps...
After evaluating my NG bills for the winter, the highest bill I had was less than $500 and that was for 32 days during that particular billing cycle including heating the ER..
I'm wondering how everybody else fared? If I wouldn't have made these changes, I would have been forced to shut down most of the winter since there is no way we could have generated enough income to run the old Jarco that I replaced. With the current cost, even with such a cold winter, it was manageable. Didn't make as much, but still was able to pay bills and stay open without going in the hole. Next winter, I will definitely be more proactive and raise prices accordingly.
After evaluating my NG bills for the winter, the highest bill I had was less than $500 and that was for 32 days during that particular billing cycle including heating the ER..
I'm wondering how everybody else fared? If I wouldn't have made these changes, I would have been forced to shut down most of the winter since there is no way we could have generated enough income to run the old Jarco that I replaced. With the current cost, even with such a cold winter, it was manageable. Didn't make as much, but still was able to pay bills and stay open without going in the hole. Next winter, I will definitely be more proactive and raise prices accordingly.
I am planning on ripping out some boilers pretty soon too. I have done several tankless setups in the past. However, on these next ones, I am planning on using one tankless 400Kbtuh unit to feed hot pressurized water to a gravity tank. Then have one 400kbtuh tankless heater set up in recirculation mode to the gravity tank to keep it hot. The gravity tank will primarily fill with hot water, but I will have a lower float in the tank that will fill with cold water when the system demand is too much for the first heater. The t-stat for the recirc pump will be set about 5 degrees less than the fill tankless water heater will output, so the 2nd heater will only have to come on to 'keep hot' or to heat cold water coming into the tank during high demand. While this setup isn't new for me, the next part will be: I plan on ripping out the floor heat boilers (I really need the space) and installing a heat exchanger instead of the boiler. The heat exchanger will just be ran inline with the recirculation water heater. My only concern is that if the place looses power for a period of time during extreme cold, then starts up with below freezing glycol pumping through the exchanger - I may end up freezing the water side of the heat exchanger doing some serious damage. I may have to have some temp sensor that will protect this from happening and have to be manually ran til the glycol heats up some.... We will see how it goes. This should save some bucks. I will be taking out 2 million btuh worth of heaters to do the same job with 800kbtu. I hate seeing the 1.5 million btu boiler firing up for 4 seconds to heat up a 25 gallon tank 5 degrees when one customer is using a bay. What a stupid set up.
6 self serve and an automatic and we replaced 2 million total btus. We have 1- 250,000 btu boiler that has heat exchangers plumbed in and it will do floor heat and other hot water with few problems. It is set up so that hot water is the priority so it just goes back to floor heat when hot water catches up. On those few days when we are backed up to the street busy the water is 100 degrees instead of 135. All that being said I think If I was to do it again I'd just have a conventional hot water tank for hot water and an instant hot water heater or condensing boiler for the floor heat with glycol run directly through it. If you don't care about standby losses you could use a conventional tank and recirculate it through the tank just like you're saying.
2Biz
Thread Killer!
Neat idea! Something else to consider. I recently put in a 199K BTU 55 gallon HTP Phoenix all Stainless Steel Condensing/Modulating water heater. It has 1" supply fittings and additional 3/4" fittings for space heating capabilities. This would work great for your heat exchanger without tying it all in to your float/gravity tank. With this setup, One water heater will do the work of 2 demands with no restrictions. They make ones up to 119 gallon capacity. Maybe bigger? Just thinking about this from a different angle. I'm more than satisfied with my water heater so far. Extremely efficient to operate.
Well, we use hot water rinse on our self-serve bays and heated chemical passes on the autos, and there is no way we can get by with 200kbtu. Our winter incoming water is near 35 degrees. That gives a delta requirement of 85 degrees. Each bay at 3.5 gpm and and auto or two at about the same makes a minimum of about 800kbtu for our places. The thought behind the plan is that we will often need all of the water heating capacity, but will never need all of it at the same time that the floor heat is running (on those buys winter days, the hot water keeps the bay floor concrete warm enough on its own. The heat exchanger is necessary because I have to heat water, but want to use glycol to run through the bay floors for floor heat. I don't see any way around a heat exchanger unless I keep the old floor heat boilers or get new boilers/heaters. The heat exchangers should be near 100% efficient, and if you add in the fact that I would be using existing heat that was already supplied for something else (the gravity tank) that would bump the floor heat system up to maybe 110%(?) efficient...
One of the biggest reasons that I am doing this is that I need the room in the equipment room. So I don't see those as feasible. Also, I need about 25 gallons per minute, since they run constantly all day on busy days. Three of these sites are 6 plus bays and 1 automatic. One is 4 plus 2. They are very busy locations. 816 gph is only 13.6 gpm, so I don't think it will stretch. I like the idea of the auxiliary connection, but is that a heat exchanger connection... further, does that mean you can run glycol through the auxiliary connection and water through the displayed connection?
To answer the 110% efficency question: If you are using heat from an 'outside of the system' source, that is like free energy compared to what is there now. It is 110% or whatever it works out to being because a heat exchanger has no real losses. There is no fire there either. Just like an immersion electric heater is 100% efficient because all of the energy used goes toward heating, the heat exchanger looses all of its heat to the glycol system, which is the intention anyway. The 'whole system' however would not be 100% efficient due to the water heater loosing heat through the flue compared to the gas burned. I like the idea of using heat that would be wasted though, to provide heat to other systems.
To answer the 110% efficency question: If you are using heat from an 'outside of the system' source, that is like free energy compared to what is there now. It is 110% or whatever it works out to being because a heat exchanger has no real losses. There is no fire there either. Just like an immersion electric heater is 100% efficient because all of the energy used goes toward heating, the heat exchanger looses all of its heat to the glycol system, which is the intention anyway. The 'whole system' however would not be 100% efficient due to the water heater loosing heat through the flue compared to the gas burned. I like the idea of using heat that would be wasted though, to provide heat to other systems.
2Biz
Thread Killer!
The auxiliary ports are not connected to a heat exchanger inside the heater. So you would have to have an external heat exchanger to heat glycol. Normally this is a no-no when it comes to heating domestic water since you can potentially contaminate the water. But since the water is used for a CW and is not consumed, I don't see an issue with it? I believe I would have tried to heat my bay floors with mine except I put a demand in for the floor heat 2 years ago. I like the idea of keeping everything as simple as possible. But, if my demand heater ever fails, I have options!
mjwalsh
6 bay SS w/laundromat
JGinther,
We have similar issues as to the space for the larger tanks vs wall mount plus heat exchangers except in our case the water serves laundromat washing machines instead of your plus 2 automatics.
Have you compared the different brands & models of heat exchangers at this point in your information gathering? We have had great results (over 23 years) with two French made Spirecs: http://www.spirec.com/
Since the glycol is way less pressure than the city water pressure side ... you should be OK when it comes to contamination. You may want to check your local codes. I know Minnesota had (& probably still has) a double walled coil stipulation.
Also, you gain efficiency by not having the glycol being heated by a gas burning combustion process .... because of the specific gravity of glycol vs the specific gravity heat transfer efficiency of water.
mike walsh www.kingkoin.com
We have similar issues as to the space for the larger tanks vs wall mount plus heat exchangers except in our case the water serves laundromat washing machines instead of your plus 2 automatics.
Have you compared the different brands & models of heat exchangers at this point in your information gathering? We have had great results (over 23 years) with two French made Spirecs: http://www.spirec.com/
Since the glycol is way less pressure than the city water pressure side ... you should be OK when it comes to contamination. You may want to check your local codes. I know Minnesota had (& probably still has) a double walled coil stipulation.
Also, you gain efficiency by not having the glycol being heated by a gas burning combustion process .... because of the specific gravity of glycol vs the specific gravity heat transfer efficiency of water.
mike walsh www.kingkoin.com
MJ, Thanks for pointing out that brand. I saw on the website that somehow they are freeze tolerant...? My concern was that if the system somehow turned on when it was off for a long time (like if power was lost when below 0 out) and then came back on, the temperature of the incoming glycol would be cold enough to freeze the water side and damage the units... While I can work around this, it would be good peace of mind to know that freezing may not cause any damage. I wonder how in the world a water pipe could be freeze tolerant...? hmm.
So what is the purpose of using them in your application? Reason I ask is that at one location that is a 6+1, we are making a new laundromat (the building was originally constructed to be one 20 years ago - but the owner decided last minute to put in a tanning salon). Was it that you needed different temperatures for each application (but you could use a mixing valve for that...)? I may be looking into doing something creative for the laundromat, as it will be packed with washers and have very little space for an "equipment room".
So what is the purpose of using them in your application? Reason I ask is that at one location that is a 6+1, we are making a new laundromat (the building was originally constructed to be one 20 years ago - but the owner decided last minute to put in a tanning salon). Was it that you needed different temperatures for each application (but you could use a mixing valve for that...)? I may be looking into doing something creative for the laundromat, as it will be packed with washers and have very little space for an "equipment room".
mjwalsh
6 bay SS w/laundromat
JGinther,
We actually have had the same potential as you describe & even more so because of the -30° F design of our system & North Dakota winters. I think you will find that by the time the concrete deicing slab lowers to even close to that low of temperature the no heat condition will be seen & quickly solved. We have alarms that trigger if temperatures of any fluid gets too low or too high. On our Spirecs we have boiler water on one side & glycol on the other so we do not have to be concerned about hard water scaling. Our domestic water is in three stainless tanks each with a single wall copper Amtrol heat exchanger inside of them. Amtrol now sells the stainless versions of these. Had we known Amtrol was going to correct there non stainless tanks we would not have had our stainless tanks fabricated locally.
The reason for going to the Spirec was to be able to bypass our less efficient Raypac. Both the mechanical engineer & the plumbing contractor on the update were against the Spirec Brand even though I explained to them the smaller footprint of the Spirec was the only one that would fit spatially. We use our 450K modular 3 unit Hydrotherm Multipulse system with priority going to the domestic. The two Spirecs allow us to draw heat off of that 92% plus system for the glycol in our Trane Hot Water fan driven space heaters in 3 of the bays & for the glycol for the deicer in the other 3 bays & the floor heat in the dog wash. If the domestic water priority causes the glycol in the bays to get temporarily behind ... it is not really a problem since our customers really mostly expect the car wash to not be freezing.
There are a lot of components that need to work in unison. Johnson Controls on the electrical were involved back in 1985 but much of there components have been updated since. One key component replaced was to go to a 1-1/2 Belimo 3 way valve diverting valve that replaced the 1-1/2" Johnson Control 3 way diverting valve. the Belimo was much better. We have a Belimo 3 way proportioning valve in the dog wash that works off of a PID loop with the PLC. Another Belimo 3 way proportioning valve is used with a PLC PID loop to control a vent for make up air.
We plan on adding a wall mount tankless to allow for increased business & more people choosing hot water with fewer fills on our washing machines. Space was the primary factor for the tankless. Since the tankless is more efficient with colder inlet temperatures ... we will have to pay attention to the controls & the flows.
To get both the domestic & the heating system perfected for your specific needs like 2Biz did can be a major challenge ... so hopefully you allow enough time etc to pre-plan etc. The engineer who I grew up with gave me some very good advice ... he said if the system can't be done on paper before hand ... there is a very good chance it will not be successful.
mike walsh www.kingkoin.com
www.wea-inc.com/pdf/mod-hydr.pdf With plumbing to match the graphic at the top of this page in combination with a thermostat like used in a walk in cooler for freeze protection you should be ok. (It turns the glycol pump off if it's below 35 or whatever) So the secondary pump loop would be where the glycol side of your heat exchanger is.
2Biz....I love your setup.
In studying tankless hydronic heating....I found a website that raised concerns about reliability. It seems some contractors have had problems since most units were NOT made for a 50% duty cycle.
Although my old RayPaks send 20+% up the stack.....they are indeed RELIABLE. It wouldn't take much to have my floor heat go out on a crazy winter weekend and ruin the cost savings from an efficient system.
How do you feel about reliability?
Also...
Here in PA, I'm told that ASME is required when used in a hydronic system. With Domestic Hot Water....not so as long as the input is less than 200K BTU's. I also have been told (does anyone know for sure?), that daisy chaining 199K BTU units does NOT trigger the ASME requirement.
When does the ASME requirement take hold? I'd hate to have a sweet system like 2Biz's....and then be told to rip it out because it doesn't meet code.
In studying tankless hydronic heating....I found a website that raised concerns about reliability. It seems some contractors have had problems since most units were NOT made for a 50% duty cycle.
Although my old RayPaks send 20+% up the stack.....they are indeed RELIABLE. It wouldn't take much to have my floor heat go out on a crazy winter weekend and ruin the cost savings from an efficient system.
How do you feel about reliability?
Also...
Here in PA, I'm told that ASME is required when used in a hydronic system. With Domestic Hot Water....not so as long as the input is less than 200K BTU's. I also have been told (does anyone know for sure?), that daisy chaining 199K BTU units does NOT trigger the ASME requirement.
When does the ASME requirement take hold? I'd hate to have a sweet system like 2Biz's....and then be told to rip it out because it doesn't meet code.
mjwalsh
6 bay SS w/laundromat
Rudy,
Is the inspection done by your private insurance (for example Hartford Boiler Insurance) & just supervised by a state agency? My understanding in our state of ND when I asked about us potentially putting in a tankless to supplement our existing non boiler water side ... it would not be on their included list regardless of BTUs. ASME is mainly for tanks. In our case our boilers are referred to as ASME pressure vessels. We have 5 small boilers between 150K & 199K (our Raypak) within our that is used both for Domestic Hot Water & closed loop such as our, baseboard units, Trane Unit Heaters in some bays, floor heat (dog wash), & deicer in some other car wash bays. I don't believe Domestic Hot Water is their main criteria whether used in residential or commercial which would be our case. Each boiler is usually charged a fee even if they are very modular like you propose. Tying in to existing closed loop boiler water could be a technicality that would need to be clarified.
Something to consider ... since the specific gravity of antifreeze causes less efficiency when it goes through the fire chamber anyway ... it may pay to check into a Spirec in line heat exchanger ... we have used two of them for over 25 years now. That could even have a bearing on whether the inspector decides that the tankless is not physically part of the fire chamber boiler water but just acts as a tankless heat exchanger for the Hydronic.
I would send the relevant chief boiler inspector an email so you have something in writing both on your info request & their response as to where you might potentially stand. Hopefully, he or she will let you know if it is unlikely the policy will change so you don't get blindsided later on. Even if ASME is not the issue ... it is still better not to have to have too many extra boiler inspection fees ... that can add up over the years.
mike walsh www.kingkoin.com
2Biz
Thread Killer!
Rudy,
Prior to my upgrades, Floor Heat Boiler and High Efficinecy Hot Water Heater, I had (2) 350K BTU Jarco's in the ER. Neither worked....But I also have never had an inspection....Although I was told that anything under 199K did not require an inspection. I also understood that if you put more than one 199K in series, this still falls under the same guidelines or restrictions. But before pulling the trigger, I'd do lile Mike suggests, contact your chief boiler inspector and ask what the requirements are.
As for reliability and duty cycle, mine cycles on and off about every 10-15 minutes...15 minutes on - 15 minutes off below freezing. The colder it gets below freezing, it will stay on a little longer and off times will be a little less, but it self regulates. Last winter, we had -16° weather. I have weep that runs across the floor and it never froze. That is with 90° glycol going out to the bays. The heater is set at 105°. Return glycol stays between 60° and 75°. I have a 15° temperature differential set on the return line t-stat that cycles the heater pumps. In January, it didn't get above freezing here much...If any. It ran the whole month. I heat the ER and floors for a 4 bay (One Bay completely outside) and my highest NG bill was less than $500.00. We had 10-12 inches of snow several times and the outside bay would keep the snow melted. The 199K btu Takagi cost $1350....98% efficient. SS heat exchanger...6 amps total for (3) 120v pumps when they are all running....2 years on the system///Zero Issues...I couldn't be happier..
Prior to my upgrades, Floor Heat Boiler and High Efficinecy Hot Water Heater, I had (2) 350K BTU Jarco's in the ER. Neither worked....But I also have never had an inspection....Although I was told that anything under 199K did not require an inspection. I also understood that if you put more than one 199K in series, this still falls under the same guidelines or restrictions. But before pulling the trigger, I'd do lile Mike suggests, contact your chief boiler inspector and ask what the requirements are.
As for reliability and duty cycle, mine cycles on and off about every 10-15 minutes...15 minutes on - 15 minutes off below freezing. The colder it gets below freezing, it will stay on a little longer and off times will be a little less, but it self regulates. Last winter, we had -16° weather. I have weep that runs across the floor and it never froze. That is with 90° glycol going out to the bays. The heater is set at 105°. Return glycol stays between 60° and 75°. I have a 15° temperature differential set on the return line t-stat that cycles the heater pumps. In January, it didn't get above freezing here much...If any. It ran the whole month. I heat the ER and floors for a 4 bay (One Bay completely outside) and my highest NG bill was less than $500.00. We had 10-12 inches of snow several times and the outside bay would keep the snow melted. The 199K btu Takagi cost $1350....98% efficient. SS heat exchanger...6 amps total for (3) 120v pumps when they are all running....2 years on the system///Zero Issues...I couldn't be happier..
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The rules for PA seem to match that of Colorado... ASME is required on any hydronic heating system, but not on domestic water heat. I have seen one car wash that had a floor heat system installed by a car wash distributor in this area where the state inspector did make the owner tear out a new Paloma tankless floor heat system and have a local heating contractor install a regular boiler instead. The same rules also apply for the btu rating, which is why there are so many manufacturers offering a 199,900 btu/hr rating and controllers to run several in parrallel. It would be cheaper to have larger units, but the gov't doesn't figure that matters I guess - just spend more money going around the red tape and they are fine with that...
You are also right about reliability, but you have to weigh that against efficiency. What makes you think the old raypaks send only 20% waste? It may be much higher than that. The thermal efficiency stated on a 'dumb' boiler is only slated for ideal sizing and flow settings and proper run times and temperature deltas. The smarter tankless units can adjust to a lot of those variables. On the other hand, the heat exchangers and construction of the components pales in comparison to old boilers... You definitely won't get the life expectancy out of the tankless units, but they may have paid for themselves a couple of times first... BTW, there are ASME tankless units out there. They usually cost a little more because they have a sticker - but some of them are actually made with thicker heat exchangers, and other heavy duty components...
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