Tiny house load vs. Giant Snowmelt load; HELP!

kevin_5

This Nebraska home will be slab on grade, ICF walls dug into a berm. It will have a Peerless Pinnacle with Indirect.
My Wirsbo program says the house load is 67,000, and there is 1300sq ft of snowmelt for an additional 195,000 BTUs. I've done nice working homes, and nice working snowmelt jobs, but never one so unbalanced as this. I warned the customer the snowmelt would cost more than the house, but he wants to do it. So what would be the best way to do it?It sounds wrong to oversize the boiler 3X in order to melt snow a few days a year.Would you go separate boilers, or one big boy with a buffer tank. If separate boilers, an HX is still recommended isn't it to keep from fouling the boiler and breaking down the glycol? I know the Peerless 399 lowfires @ 100K, but wouldn't two still be cheaper and more sensible than going that route? Control strategy is also an issue. "TEKMAR, TAKE ME AWAY!"
I really need the voice of experience here. Thanks in advance guys. Kevin O. Pulver


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hr

Sounds like

a fairly large home to have that size load with a bermed, ICF construction??

I have done several snow melts with dedicated condensing boilers. It is actually a fairly inexpensive, efficient way to do snowmelt. A boiler, pump, and snowmelt control. I have used both Munchkins and one Weil Ultra with a primary loop pump, and a system pump. Glycol directly to the boiler.

With the Weil, however you need an AL (aluminum)type glycol. Nobel, Hercules, and others now offer AL propylene glycols. Cost me about $15 per gallon! Also watch the % of mix. You may want to stay in the 37-40% range as per manufactures spec.

With this wide of a load spread, go with two heat sources, IMO.

hot rod

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kevin_5

Great Hot Rod

You were one of the ones I was hoping would pick up on this thread. As you may know,after today, my favorite, most helpful wholesaler/radiant design guru (PR) doesn't answer the office phone anymore. He's in the private sector.
(I've got his cell number though, and you'll see him at Wetstock.)Anyway, the house is about 77X44, 9ft walls, with roughly 100sqft of west facing glass. I appreciate your advice. My gut feeling was these systems should be separated. No HX would save a lot of money and another circ too. Any other advice is welcomed, but it sounds much simpler already! Thanks again,Kevin

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jerry scharf_3

To make it simpler

I agree with a separate condensing boiler for the snowmelt. You could also skip on the primary/secondary for this application. Just get a pump that has the head and flow you need to cover the loops and the boiler. That would give you just about the simplest setup you could have and the coldest possible return water. (Wonder if you could get ice in the exhaust PVC pipe?)

The munchkins have a little box that you can add on that allows a dry contact to fire the boiler off at high fire, others might have this also.

jerry

hr

How about this approch, a Munchkin

feeds the inner tank (DHW) side of this Weil indirect. the four radiant floor zones also feed from this loop. The outer tank volume is glycoled to feed a 1200 sq foot snowmelt!

The snowmelt has priority and the floor zones drop off (home has 4 FA furnaces) This allows the full output of the Munchkin to do the melt.

The glycol content was small by using the outer tank of the "tank in tank" Weil indirect.

So basically the indirect's 53 gallon capacity inner tank buffers the oversized (to the radiant load)boiler, and reduces the short cycling presented by small floor zones, but I get full horsepower and ideal condensing temperatures to the snowmelt.

hot rod

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kevin_5

Thanks Jerry, but

if I piped it without primary/secondary how could I ramp up the supply temperature? Can the boiler downfire somehow to give me the low start-up temps? What control strategy are you thinking? I really like the thought of blowing ice up the flue. Snowmelt on one end, a snow machine on the other!
Kevin

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hr

How about this approch, a Munchkin

feeds the inner tank (DHW) side of this Weil indirect. the four radiant floor zones also feed from this loop. The outer tank volume is glycoled to feed a 1200 sq foot snowmelt!

The snowmelt has priority and the floor zones drop off (home has 4 FA furnaces) This allows the full output of the Munchkin to do the melt.

The glycol content was small by using the outer tank of the "tank in tank" Weil indirect.

So basically the indirect's 53 gallon capacity inner tank buffers the oversized (to the radiant load)boiler, and reduces the short cycling presented by small floor zones, but I get full horsepower and ideal condensing temperatures to the snowmelt.

hot rod

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hr

Be careful with one pump condensor snowmelts

when the glycol is cold, cold you need to assure flow through the HX. Look at the glycol and pump spcs carefully to assure flow at cold thick glycol conditions.

However I did an Ultra with a P/S and the boiler would catch up, and ramp down too quick.

If I were to do P/S again I would use the Eatherton method (lower drawing) and add a ball valve between the P/S tees to balance a little, yet still have adequate HX flow.

hot rod

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kevin_5

Another beautiful design and install HR!

Very clever. That's really got me thinking. (I love the REMScurvo work on your other post by the way.) Do you think it would still be better to go with the 2 separate boilers as far as price and performance go, or what would you say are the pros and cons of each design? And Would you use a Tekmar XXX (I forget all the numbers) with VSIM to do the mix? Thanks again, Kevin

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hr

No need to use

any mixing device with a condensing boiler/ snowmelt. Condensors will get along great with 32° or lower temperature fluid. As long as it is still in the liquid form

Ideally I would like to see a dedicated, sized to the load, condensor for the snowmelt, and the same for the house system.

Get both boiler sized as close to the load as possible. I would not advise a 399,000 just to handle the snowmelt, then try to "simmer it down now" for that small radiant load.

In my case I had that 2 square foot "footprint" to accomplish heat and snowmelt with only one appliance. Odd considering it was an 8000 square foot home!

All I did was use the indirect as a water to glycol HX. Really that is all an indirect really is, a large water content HX

hot rod

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S Ebels

I second that

With the amount of difference you have on this job, I would definitely install a dedicated boiler for each system. If you don't you're going to wind up with a compromise on one end or the other. Hot Rod has it right.

kevin_5

I'm almost with you HR

I understand how and why you did that job with the large indirect acting as a buffer tank/HX. And I'm with you on separate dedicated boilers sized to each job to avoid short-cycling. I understand that a condensing boiler LOVES those cold return temps from the snowmelt. But I'm a bit confused as to controls. To avoid thermal shock to the concrete, don't I need a control to slowly ramp up the temp as I've always done? Or is that now deemed overkill, or am I misunderstanding something? Thanks for sharing your experience with me. Kevin

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Paul Rohrs

Bic lighter and a glass of water....

Kevin,

Brother, are you abandoning my idea of a bic lighter and glass of h20?

Rest assured, this post is full of sage advice.

I am now on the same side of the counter as you, but I am always available.

I am following up with the guys at Lincoln Win about your hole-saw.

Regards,

PR

jerry scharf_3

Can't imagine why simple controls won't work

Kevin,

My thoughts on controls: One snow sensor switch into the TT input, a relay to bring on the pumps if the boiler doesn't do it. A fixed water target temperature, maximum firing all the time.

If your flow rate is set for 25F delta T at 199MBH firing, why do you need to start it up slowly? You get 32F (or below) water and send it out at 57F. Until the slabs start to warm up, you will be always getting near 32F water back to the boiler and the output will still be in the 60F range.

Is there someting I am missing?

jerry

kevin_5

Well,

> Kevin,

>

> My thoughts on controls: One snow

> sensor switch into the TT input, a relay to bring

> on the pumps if the boiler doesn't do it. A fixed

> water target temperature, maximum firing all the

> time.

>

> If your flow rate is set for 25F delta T

> at 199MBH firing, why do you need to start it up

> slowly? You get 32F (or below) water and send it

> out at 57F. Until the slabs start to warm up, you

> will be always getting near 32F water back to the

> boiler and the output will still be in the 60F

> range.

>

> Is there someting I am

> missing?

>

> jerry





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kevin_5

Well...

I'm not sure Jerry, Maybe I'M missing something. My thinking was that the boiler would provide too much heat at once and thermal shock the concrete slab. I know the boiler needs no protection, but I thought the boiler temp had to be ramped up slowly to protect the slab. Are you guys saying that at full fire the boiler will still only be able to throw a gradual heat into the slab, so it won't get shocked? No fancy control needed with a ramping target temp, a timer, and backlit LCD display in a lovely blue box? PR, jump in here and talk to me will ya? Kevin
THanks, Kevin

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hr

Boiler to slab

would work fine. Remember with a condensor you just set the required design temperature. So if the snowmelt design requires 110° just set the boiler control to that. Trust me the slab will be snow free long before it gets to 110° A slab sensor or post mounted (less expensive) ETI control would be just fine.

Remember 1300 square feet of concrete is about 16 yards or 64,000 lbs. Be hard for a properly sized boiler (1300 X 120 btu/ sq. ft. = 156,000 BTU/ hr) to ramp up that much concrete too quickly :)IMO

Any control that pulsed output to the slab would just slow the process of the melt. Exactly what you DON'T want with a snowmelt

Keep in mind glycol, by nature, soft starts an outdoor slab. When it is cold, say 32° it is thick and slower pumping than 120°. So you actually flow slower until the fluid slowly warms. That's where the PS piping comes into play. It allows the boiler HX and loop to get adequate flow, and run warmer, even though the slab may be 32° or below.

So in essence you do have a blend point of boiler temperature and melt return temperature at that closely spaced tee connection, with P/S piping.

The HDS software could calculate that °number exactly, by the way, in the "VS injection module", and determine those cold glycol fluid factors of the glycol mix

Now if you were to connect a 5 million BTU boiler and pipe it to that flow rate you might shock that 1300 square foot slab But you wouldn't do THAT. Would you?

hot rod

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Mark Eatherton1

I'd split em...

right down the middle. Part load efficiency of condensing boilers is very effective with the new modulating technology. It's going to cost more to split them, but will come back in spades in energy savings. By using stage two (space heating) interlaced into the snow melting system with a flat plate HXer, you can also provide back up redundancy in case the space heating boiler decides to take a vacation. You can also prioritize the space heating system.

Although the turndown capability of this condensing technology is wonderful, it does have its limitations, and those limitations could get you into a short cycle scenario that would cost the operator in fuel expense as well as wear and tear.

On my own system, the boiler is on the majority of the time, running at idle, which is extremely efficient (98 to 99%).

As it pertains to snowmelt, similarly to space heating, it is RARE that you are actually at your maximum full load design condition. I'd recommend you bury a sensor out in the snowmelt system between two tubes, and utilize the new tekmar modulating capabilities to modulate your boiler fire around a set point of say 35 to 40 degree slab temperatures. This way, the boilers will start modulating around the true load instead of modulating around a fixed water temperature. If the wind is blowing and its cold outside, the slab will see this loss factor, and so will the boilers.

Take lots of pictures:=)


ME

Mark Eatherton1

Shocked slabs...

Kevin, I've been looking at a lot of slabs that are all sized at 150 btu/sq ft /hr, and I've never seen one that was shocked.

I think I've seen pictures of one that was driven by an overzized steam boiler/heat exchanger combination at a hospital (350 btu/sq ft/hr), but I have yet to see one in real world applications. I tried googling, and got "Your search - thermally shocked slab - did not match any documents"

I think it's hype on the part of the controls companies more than reality. Anyone else care to counter, please do so, but my 31 years worth of experience says else wise.

The worst thing I've seen happen to a snowmelt system was one where the "hydronic expert" that installed it also made a solid make up connection to the system. For whatever reason, the system fluid went into dillution and all the glycol went away, then all the tubing froze and you could see where EVERY foot of tubing was due to the cracked and spalled slab... now THAT is my idea of thermal shocking:-) Just on the opposite end of the thermal scale.

Not to worry...

ME

Paul Rohrs

Sooooo...

Are we talking about using a setpoint control to actuate the system on and off manually?

Let's say a Tekmar 501 with slab sensing capabilities to manually control that will enable a snowmelt system pump that will send a closed end-switch signal to the boiler TT? Let the modulating boiler control do the rest? I guess it's so simple that I couldn't "see the forest because of the tree's".

I was always concerned about slab protection and I believed the Sales mantra of the manufacturer. Are there any RPA standard guidelines for snowmelt control? My books are at my new work establishment.

HydronicsMike, what say you on this?

Regards,

PR

Mark Eatherton1

Not that simple...

Something needs to detect OSA and moisture, like the ETI snow switch. It wakes up the rest of the system and enables the set point controls.

I can tell what Mikes gonna say.. But I'd rather he speak for himself:-)

See you at RPAW!

ME

hr

Control options

for entry level the ETI sensor is a deal. It mounts outside on a pole or roof. Slab sensors ar nice tekmar, Heat Timer, Caleffi and a few other have them.

I ALWAYS add a 12 hour spring wound timer, regardless of a slab or less expensive automatic control. This allows the homeowner to "call" on the snow melt in anticipation of a storm. Never use a plain on/ off switch for manual operation!

With a condensor all you need to do is make the "tt" conection with whatever type of mild, or wild, control you chose. Most boilers have pump contacts included. This could control one, or both pumps, depending on the rateing of that relay. worse case you add a realay for the system pump if you go P/S and have two pumps.

Contact Robert Bean, he is a snowmelt guru extrodinare. Instrumental in the RPA snowmelt guidelines and action commitee, and the updated ASHRAE snowmelt guidelines. He spoke here recently about Michelle Shocked concrete.
Funny guy, too

hot rod

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Kal Row

2 ultra's sized 70% total each, and 2 ultra plus indirects...

dont like to have all my eggs in one basket
also dont like to mix or feed supercooled glycol mix to a heat source without a large buffer - call me chicken!

recomend take total btu load for heat/dmhw/snow
get two utlra's each equal to 70 % of load, and
use am4 module for each and a tekmar 265 to control them,
(am4 is an extrnal mudulating interface to boiler,
tekmar265, can control and modulate up to three modulating boilers)

use a plus 40 for you dmhw needs - run it at 160 and antiscald mix it down to 120

and a plus 80 for your snowmelt

dont skimp on the boiler room pumps or pipes, use high GPM pumps and large 1-1/2+ pipes to the indirects - as the utra-plus is a tank within tank design, not a coil and needs high gpm to do it's thing

cant see how such a system will let you down



and please read siggi's artical about bottlenecks
http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,146193,00.html

leo g_13

Hey HR, what is this

post mounted ETI control, and who sells it? I had an electrician friend contact me about a job that he was on where the snowmelt, controlled by a Callifi, will not start automatically. The sensor is mounted in the driveway, that drops at about a 15 degree slope. I couldn't figure out a way to fix it without tearing apart this piece of the driveway. Couold this be the solution?

Thanx!

Leo G

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leo g_13

High end controls

do come in handy in my area. A common winter event here, is rain all day, clear up quickly and FROZEN roads and driveways. That of course then get a good dump of snow! The ability of these controls to pre-warm a slab or idle at a bit above freezing is an asset for times like that.

Leo G

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Kal Row

question for M.E...

why doesnt a plastic soda bottle crack at -5f, yet pex does?

Kal Row

glycol on the outside tank... as long...

as the pressure in the inside tank is gauranteed to be always higher than the outside tank - or you can get buckling and seam breakage of the inside tank


you can cut a 1/4 inch slice out of any tank, and get 4 people to pull outward and it wont break, but 1 person alone can collapse the cut ring inward


this is why you need to isolate the hot water heater when using a shop vac to winterize a house - even a little vacum will bend it enough to crack the glass lining

Mark Eatherton1

Here you go Leo...

http://www.networketi.com/

Put them somewhere that you can service it. The snow sensor reequires regular cleaning (as they ALL do...)

ME

Mark Eatherton1

Beats me...

My guys were trying to install some PEX at around 5 above F, and every once in a while, the tube would SHATTER...

Bottles are made of a different plastic, PTFE if I'm not mistaken. Could be they have more give to them.

ME

Kal Row

does pex-al-pex exhibit this cracking too?

Kal Row

on second thought..after reading the plus manual again...

and again...
make it a plus for DMHW and a solar coil type for snowmelt cause the PLUS might not be the perfect fit for a snowmelt buffer:

1)who wants to worry about having the pressures right - the "filling / draining" warning on page 19 of the plus line manual leads me to believe that 15psi higher in the outer tank is the limit for the outer greater differential – for the inner to outer – use info from pg 5 – 150 max inner and 45 max outer = 95psi inner greater differential

2)even the outside tank requires too much glycol

3)the flow requirements are too high for the pex world, while that’s ok for sourcing a huge snowmelt manifold (like this one) - but for the avg home - a coil in tank design, might be a better fit - specially the kind used for solar with the coil exiting up higher, and the coil part being the snowmelt loop

jwade55_3

I use the ETI..

In conjunction with a Ranco ETC-111000 thermistor based temperature sensor, have the installer run some conduit in between two tubes, insert the sensor, power the ETC thru the relay of the ETI, with the ETI relay bringing on the boiler, with a timer as HR mentioned for an override. Have got about 20 like this, and seem to work well. Cleaning the eti sensor is important.

Also most of these are using Condensing boilers, primary secondary the way HR showed with the boiler internal controls doing the temperature control.

J

Mark Eatherton1

I think...

that ANY semi rigid conduit (exception being rubber hose) is going to exhibit the propensity to burst due to the contained fluid expanding by 1/5th its original volume. If its not contained, then its not an issue. If it is tube locked, it IS an issue. It generates upwards of 20,000 PSI of pressure when it freezes and expands by 1/5th its original volume. There are not many materials that can withstand that kind of pressure, and concrete is NOT one of them.

As for rubber hose, I would think that even it might show the ability to spall concrete if it were filed with water, placed in cement and allowed to freeze. Due to its elasticity, it may not burst, but it probably would rupture the metallic oxygen barier, if it had one...

But then again, I'm just a stinkin' hot water heating plumber roamin' around on the plains of Colorado, lookin' for broken snowmelt systems.... What do I know:-)

ME

Kal Row

ah, ya kill me )

kevin_5

Thanksa bunch guys!

I really appreciate all the input! It's incredible how fast you can get educated at Holohan U. Kevin

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Tim Doran

800-3321-4739

Give me a call if you would like to discuss options.

Tim D.

Tim Doran

800-321-4739

Give me a call if you would like to discuss options.

Tim D.

Nick_16

Reply

I'd hate to see his gas bills! LOL