tankless vs indirect for DHW in coal boiler

Re: tankless vs indirect for DHW in coal boiler

PostBy: Lightning On: Sun Mar 02, 2014 2:30 pm

Carbon12 wrote:An indirect is like a domestic hot water coil in a boiler but in reverse. Instead of the large volume of water in the boiler heating the DHW in the coil, the indirect has the coil heat the larger volume of water for DHW.
:shock: oh... thanks! Now I better understand what Larry was saying. That clears it up for me... 8-)

Case of inverted perspective again.. I was looking at it wrong. :lol:
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: tankless vs indirect for DHW in coal boiler

PostBy: lsayre On: Sun Mar 02, 2014 2:38 pm

Rob R. wrote:They also make reverse indirect water heaters. :)


Having one of these is a lot like using the boilers own internal DHW coil. But it offers the advantage of effectively doubling the water capacity of your boiler, and its internal coil is most likely going to have a lot more length and therefore surface area than a typical boiler installed coil, so it should work much better overall. If your boiler doesn't have a coil this is an alternative.

Having used an internal boiler coil for nearly 3 years now I can say that it does work well most of the time, but occasionally if multiple zones are firing at the same time as you are showering, the shower can go 'tepid' on you. It's happened twice to me so far this year, with both times being in January. I believe the best system to use with a boiler is a standard indirect tank on a zone system. Not a reverse indirect, or an internal boiler coil.

I just took a nice hot shower using the DHW coil. No zones were calling for heat during my shower to my knowledge. I've learned to shower when no zones are calling for heat via T-Stats. Generally right after the boiler has satisfied all of the zoned T-Stats and shut down its fan is the best time to shower. But in the cold of the winter its hit or miss, as a T-Stat can call for heat at just about any time. And if two or more of them are calling a tepid shower may just be the consequence.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: tankless vs indirect for DHW in coal boiler

PostBy: Pacowy On: Sun Mar 02, 2014 2:50 pm

Rob R. wrote:Tankless coils work well with boilers that have sufficient mass and btu output.


x2. If you have plenty of available mass and btu output, a tankless coil is simple, comparatively inexpensive and highly effective.

Mike
Pacowy
 
Stoker Coal Boiler: H.B. Smith 350 Mills boiler/EFM 85R stoker
Coal Size/Type: Buckwheat/anthracite


Re: tankless vs indirect for DHW in coal boiler

PostBy: Lightning On: Sun Mar 02, 2014 2:57 pm

Ok so, if I understand everything right, a tankless coil is just what it implies. Cold water is heated by a coil in the boiler then "directly" goes to where its being demanded.. Where as an indirect has a coil in the hot water tank that is regulated by a boiler zone.. Thanks for the lesson. I plan to go hydronic at some point. This is all valuable information.. :)
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: tankless vs indirect for DHW in coal boiler

PostBy: lsayre On: Sun Mar 02, 2014 3:00 pm

Lightning wrote:Ok so, if I understand everything right, a tankless coil is just what it implies. Cold water is heated by a coil in the boiler then "directly" goes to where its being demanded.. Where as an indirect has a coil in the hot water tank that is regulated by a boiler zone.. Thanks for the lesson. I plan to go hydronic at some point. This is all valuable information.. :)


If you go with a boiler coil be sure to run its output through an anti-scald (mixing) valve that moderates it to a set output temperature that is safe. When my system gives me a 'tepid' shower the boiler water is still at a seriously scalding 150 degrees. It seems that that my particular mixing valve requires water that is at lest 160 degrees inside the boiler in order to provide an enjoyable 'hot' shower. I believe that most comfortably "hot" showers are taken with water that is only about 105 to 110 degrees F.
Last edited by lsayre on Sun Mar 02, 2014 3:05 pm, edited 1 time in total.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: tankless vs indirect for DHW in coal boiler

PostBy: Rob R. On: Sun Mar 02, 2014 3:02 pm

lsayre wrote:
Lightning wrote:Ok so, if I understand everything right, a tankless coil is just what it implies. Cold water is heated by a coil in the boiler then "directly" goes to where its being demanded.. Where as an indirect has a coil in the hot water tank that is regulated by a boiler zone.. Thanks for the lesson. I plan to go hydronic at some point. This is all valuable information.. :)


If you go with a boiler coil be sure to run its output through an anti-scald (mixing) valve that moderates it to a set output temperature that is safe.


That is a good idea on an indirect also. It is common for HOT water to collect at the top of the tank under certain conditions.
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy

Re: tankless vs indirect for DHW in coal boiler

PostBy: windyhill4.2 On: Sun Mar 02, 2014 3:23 pm

We enjoy endless hot water from our water to water plate exchanger,no matter if the heat is also running.
windyhill4.2
 
Hand Fed Coal Stove: Crane 404 with variable blower
Other Heating: Oaktree OWB 600K

Re: tankless vs indirect for DHW in coal boiler

PostBy: lsayre On: Sun Mar 02, 2014 3:39 pm

windyhill4.2 wrote:We enjoy endless hot water from our water to water plate exchanger,no matter if the heat is also running.


How big is your reserve tank that has the exchanger in it? And how much water does your boiler have in it?

My boiler only has a paltry 27 gallons of water in it, and each of my 4 zones probably have about 5 gallons of water in them. Dropping 5 gallons of cold zone water into 27 gallons of hot boiler water can drop the boiler temp noticeably, and if two or three zones (let alone 4) are open at once it can really bring the temp down. But I set it up where my circulator shuts off whenever the calling zones bring the boiler down to 150 degrees (turning on again at 160 degrees), so it rarely goes below 150 degrees. I had considered getting a 27 gallon reverse/indirect HWT at one time to double my boilers water capacity. That would most likely give me endless hot DHW.

For one cold (60 degree water) zone calling and the boiler at 180 degrees:
27(180) + 5(60) = 32(x)
32(X) = 5,160
X = 161 degrees boiler (entire loop) temp

For two cold (60 degree water) zones calling at precisely the same time and the boiler at 180 degrees:
27(180) + 10(60) = 37(x)
37(X) = 5,460
X = 147.5 degrees boiler (plus both loops) temp

Etc...

But double my boilers capacity and all 4 cold zones firing simultaneously suddenly looks like this:
54(180) + 20(60) = 74(x)
74(X) = 10,920
X = 147.5 degrees boiler (plus all 4 zones) temp

Suddenly my worst case scenario is 147 degree water. And I have almost never seen all 4 zones firing at once, let alone having them all initiate their call for heat at the exact same time.
lsayre
 
Stoker Coal Boiler: AHS S130 Coal Gun
Coal Size/Type: Anthracite Pea
Other Heating: Resistance Boiler (if I ever get it fixed)

Re: tankless vs indirect for DHW in coal boiler

PostBy: windyhill4.2 On: Sun Mar 02, 2014 5:16 pm

OWB holds 200 gals,the plate exchangers are on a loop that is always circulating,there is no reserve tank unless you count 800+ feet of 1 " pex as a reserve tank.
windyhill4.2
 
Hand Fed Coal Stove: Crane 404 with variable blower
Other Heating: Oaktree OWB 600K

Re: tankless vs indirect for DHW in coal boiler

PostBy: Rick 386 On: Sun Mar 02, 2014 11:13 pm

lsayre wrote:......................I just took a nice hot shower using the DHW coil. No zones were calling for heat during my shower to my knowledge. I've learned to shower when no zones are calling for heat via T-Stats. Generally right after the boiler has satisfied all of the zoned T-Stats and shut down its fan is the best time to shower. But in the cold of the winter its hit or miss, as a T-Stat can call for heat at just about any time. And if two or more of them are calling a tepid shower may just be the consequence.



I have become accustomed to listen for the AA to fire and shut of BEFORE I go for my shower as I'm the last one each day to get one. And yes I have gotten a "tepid" shower many a times. In my case, it means turning the valve to all hot vs. having it at about a 1:00 position as I also do have a mixing valve on it.

Doesn't really bother me as this is just one of the quirks of heating with cheap coal.

And since I'm the one who advocates for the 24/7 365 burning of coal, I'll deal with it. The issue becomes a real problem only when the spousal unit is the one who gets the "tepid" shower.




Rick
Rick 386
 
Stoker Coal Boiler: AA 260 heating both sides of twin farmhouse
Hot Air Coal Stoker Stove: LL Hyfire II w/ coaltrol in garage
Coal Size/Type: Pea in AA 260, Rice in LL Hyfire II
Other Heating: Gas fired infared at work

Re: tankless vs indirect for DHW in coal boiler

PostBy: Sting On: Mon Mar 03, 2014 8:22 am

Rick 386 wrote:
And since I'm the one who advocates for the 24/7 365 burning of coal, I'll deal with it. The issue becomes a real problem only when the spousal unit is the one who gets the "tepid" shower.Rick


Shower together for "shared warmth" 8-)
Sting
 
Other Heating: BurnHAM=NG-gas

Re: tankless vs indirect for DHW in coal boiler

PostBy: Lightning On: Mon Mar 03, 2014 9:02 am

Yep, save water shower with a friend... :woot:
Lightning
 
Hand Fed Coal Furnace: Clayton 1537G
Coal Size/Type: Nut Size / White Ash

Re: tankless vs indirect for DHW in coal boiler

PostBy: Carbon12 On: Mon Mar 03, 2014 9:15 am

Or friends, plural :lol:
Carbon12
 
Stoker Coal Boiler: Keystoker KA-6
Coal Size/Type: Rice/Anthracite
Other Heating: Heat Pump/Forced Hot Air Oil Furnace

Re: tankless vs indirect for DHW in coal boiler

PostBy: Rob R. On: Mon Mar 03, 2014 9:23 am

I briefly used the tankless coil on my EFM and was not impressed at how high I had to run the feed rate to handle filling the bathtub. Don't get me wrong...I could have restricted the flow to the tub and gotten away with it, but that defeats the purpose of a "fast-fill" fixture. It wasn't a problem if the boiler had been working before the tub was filled, but if it went from running on the timer all afternoon right to the tub being filled, the boiler temp. (and tankless output temp.) would drop considerably. Increasing the feed and keeping the boiler at a higher temperature pretty much took care of it, but I also burned almost twice as much coal. I decided it was time to "go big or go home" and installed an 80 gallon indirect water heater. Now I can keep the boiler at just a simmer during the day and still have ample hot water for a "shock load" of demand at 7 pm.

Looking backwards, when using the tankless coil I probably should have focused more on insulating the boiler and piping better, and experimenting with different timer cycles...but I doubt I could have reached the same level of performance and coal consumption as with the indirect.
Rob R.
 
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Other Heating: Dad's 1953 EFM Highboy

Re: tankless vs indirect for DHW in coal boiler

PostBy: Lu47Dan On: Mon Mar 03, 2014 11:53 am

Once my system is complete, I will have a circulating pump on my hot water system that will allow hot water at the point of use in a few seconds instead of waiting for the water to come up to temperature.
The pump will circulate the hot water in a loop to the fixtures and back to the water heater.
Just before the water heater cold water inlet port I will install a shell and tube heat exchanger, this will allow me to control the temperature of the water arriving at the tank. The heat exchanger will be supplied by another circulating pump, that will be on a set of controls that will maintain a 135°F water return to the tank.
Setting the Electric Water Heaters Thermostats to 130 will allow the elements to come on IF the boiler would go out.
I have not settled on a final design for the piping of the heat exchanger yet. I could go two ways with it.
One would be to just plumb the exchanger into the recirc line, and allow the cold water to flow directly into the tank. This would work fine in when someone is washing their hands or hand washing the dishes. But has its problems when there is a large load on the system such as doing multiple loads of laundry or multiple people taking showers. The heat exchanger would be bypassed in this piping lay out.
Second would be to pipe both the recirculated water and the cold water through the heat exchanger. In this piping lay out all the water would flow through the heat exchanger and be heated by the boiler.
Both of these require process controllers, either aquastats or PID controllers to prevent over heating of the incoming water. I am leaning towards a PID controller to control the temperature output of the heat exchanger.
Temperature control can be done with Tempering valves but most of them do not work well when the two temperatures are fairly close to each other, in my experience.
Dan.
Lu47Dan
 
Hand Fed Coal Stove: Sears circulator air tight stove.
Other Heating: Crown 115,000 BTU oil fired boiler(house) Weil Mclain 150,000BTU oil fired boiler(Shop)