How many circulators needed ??

JEM

I am in the process of building a new building with 4" concrete slab on grade, 3000 sq. ft. I was lured in by the "Vermont" company I see mentioned on the Wall from time to time and purchased 10, 300 ft. coils of 1/2 pex with the O2 barrier. Planning on 10 circuits @ 300 ft. each. Since this building will be pretty much 1 large room with only a bathroom I want to treat it as just 1 large zone. Will I need more than just one circulator? Also as far as manifolds go do they need split up or will a 10 outlet hot and 10 outlet return do the job? Ever since I thought about going radiant I have been reading the "Wall" daily, I seem to find a lot of knowledge hear and a bunch of downright "good" people. Thanks for any help, JEM

Weezbo

hello.

*~/:) that seems like easy enough question,3000 ' sounds like Plenty of Tubing.now depending on your control stradgey...and some times the heat plant,...the recirculators may be 1 to <11 id probably use one for the boiler and one for the system.and two zone valves one for the field and one for the boiler. one with outdoor reset and the other with set point.

Dan Peel

more stuff

Aside from the slab full of tubing what equipment do you have?
Your nominal 12"OC,1:1 density in the slab is probably fine if the heat loss is generally balanced across the floor area - are we talking about a garage/workshop type space or a living space? What geography?
The short answer to your question is one circulator may do the job from a low temperature tolerant heat supply. When you get into return temperature protection you may find it easier to work with 2 or 3 smaller circs and regionally split manifolds.
What is the design heat loss # ? What are the building use operating conditions - doors open/closed, cold equipment meltoff etc.? What have you selected to heat the fluid? Will the fluid be water or blended glycol? Is outdoor reset included in the design? Is there a DHW component?
Flesh out the package and design constraints and you will get the types of opinions you've requested here. Enjoy......Dan

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

JEM

More stuff

Dan and Weezbo, thanks for the reply. As far as equipment goes I have available an AO Smith gas fired boiler, I believe it is in the 195K BTU range. I would rather use a gas fired hot water tank to keep things simpler as this is a closed system. This will be a living space. Geography is the NE part of Ohio, average in winter months in the 30* range. Yes was planning on 12"OC possibly 6" at all exterior wall areas. 2" thick polystyrene in 4' and 1" thick in the next 4 ' from exterior walls also 2" thick up the sides to help heat loss out the sides. As far as a heat loss calc this is were you guys will give me #!**. I spoke with a local contractor that was to get this for me over 2 months ago and i am still waiting. Operating conditions will be a closed area with some thermal pane windows and doors. Fluid will be a glycol mix and as far as outdoor reset & set point I'm listening or should I say, reading! Thanks

Constantin

Have a look at Dan Holohans book...

... IIRC, he observed that concrete floors with in-place radiant systems will usually work despite bad installations, no insulation, etc. As a mere homeowner myself, I appreciated the approachable style of his book.

You might also have a look at Siegenthalers book on hydronics, there is more info in there than you'll probably need. However, it is quite hands-on and may very well answer your questions re: the manifold sizes. With that large of a floorplan, my inclination would be to have at least two manifolds, to simplify tubing layout and promote temperature eveness.

Furthermore, you could discover that some parts of the slab need more heat than others due to windows, exposure, etc. Therefore, it may make sense to allow for zoning in the future by incorporating a manifold and tube-location strategy to do so. For example, in our basement (where we have similar conditions to yours), we have a seperate loop for every room.

Also consider using a reverse return in the manifolds, i.e. the first tube on the manifold on the supply side will be the last one on the return manifold. That simplifies getting the pressures to balance across the system.

As to the number of circulators, that's another question that Siegenthalers book would answer for you. My personal inclination would be to use two manifolds with one variable-speed circulator on each. That way you can do all sorts of nifty things WRT to control strategy later on.

However, if you're only going to treat the whole place as one zone, there may be no justification for going variable-speed on the circulators. Instead, focus on a boiler that is happy to modulate and condense (if you're going to heat with gas) or (when oil) which can handle very low return temperatures (either via control strategy or piping design). Cheers!

jerry scharf_2

ready, fire, aim

Sorry to be blunt about it, but you bought the boiler before you got the heating load calculated. Go the the left pipe section of the web pages and click the free heat load calcs link. Slantfin offers a good program for free and you should get it and use it to do the calcs. If you're brave enough to order things on-line, you should be able to do this as well.

Just an intuition is that with new construction, modern insulation (vapor barrier/R19 walls/r30 ceiling) and 3000 sqft, the boiler is oversized.

10 loops of 300 feet sounds fine, and it sounds like the slab insulation is fine. As for tightening up the loops near the walls, it's partly a function of the amount of window space and wall infiltration. Feeding the hot water to the outer edge of the slab and taking the return in the middle can often deal with this using consistent tube spacing.

One frustrating part of the internet companies is that you would think by reading their stuff that once you have the boiler and the tubing, it's all simple from there. It's as easy to screw up a heating system with wrong near boiler piping as wrong runs and tubing. With a boiler that isn't designed to accept 80F return water, you could lose that boiler in a couple years without correct piping. That's an expensive mistake.

Be careful on the one zone fits all control. If you have significant solar gain from windows, that can give you one area cooked while another freezes. I'd at least look at something that breaks it into a few zones. Outdoor reset is nice, it will make things more comfortable and save energy to boot. I'd think about a tecmar controller that can do all of the functions (zoning, outdoor reset, boiler protection) in a single box and get an installer who can show you prior jobs that work right using the chosen controller.

hope that helps a bit

jerry

Constantin

Oh gosh...

Have a look at the HVAC-Calc heat-loss/gain program. For $50 you can do your home and enjoy the license to do so for up to two months. Plenty of time for most homeowners to get it done, IMHO. A good second opinion at the very least.

The boiler seems completely oversized unless you're living in a uninsulated home. The reason I say this is that our home will have 5,000+ sq ft and at a design temperature of -15°, the heat loss is estimated at around 106kBTU. So unless you plan on taking a lot of long, hot showers with an indirect water heater, I see no good reason to have a boiler that large.

Your plan on insulating the edges and slab is a good one. We're going 2" XPS throughout below ground, for simplicity. Presumably, you will insulate the walls and ceilings too, right? Were I to build a new home, I'd investigate SIPS as a possible wall/ceiling solution, ICFs are interesting too. Traditional stick construction is probably best suited for spray-in foam, that reduces infiltration to next to nothing (that's what we're using).

Also, remember to get a boiler that features sealed combustion. In a tight house, you don't want to be drawing air from inside the home for combustion. Not only is it inefficient, it can be downright dangerous under the right circumstances.

Lastly, I'd stay away from glycol unless it is absolutely necessary. The stuff requires some baby-sitting, pH testing and whatnot and could reduce the inside of your pipes to dust if it is allowed to go bad. Nevermind the increased head pressures and other headaches.

JEM

Ready, fire , aim guy. Hey Jerry and Constantin, only said I have AVAILABLE an AO Smith boiler, I have only purchased the tubing at this point. As far as heat calcs through Slant Fin I tried that twice with 2 letters sent to me stating that version 2.o or something would be out soon. I like the Tecmar controller idea and will check into that further, thanks for that advise. This is pole type construction with R19 in all the walls and ceilings. Now knowing that this size boiler is over kill I will need to reconsider my heat source. Still would like to use a designated gas fired hot water tank for the radiant. I will have a SCORCHED AIR back up at any rate that I Have Already purchased. It is an outside combination A/C unit and furnace unit, Mainly have it for the A/C only. Thanks again

Constantin

Umm JEM...

...where did I imply or categorically state that you were using that AO smith unit? I only stated that such a large unit would probably be overkill.

Coming back to the topic on hand, while you wait for version 2 of HE, you may want to spring the $50 for the HVAC-Calc program. Read the manual, you may discover the need to re-evaluate the purchasing decision on the AC unit, as oversized AC units spell trouble as well.

As a further suggestion, take a look over at the Insulation DoE web site and see what the recommendations are for your ZIP code. Roof systems are usually insulated more than walls to limit heat gain and loss (depending on the season).

Instead of considering water heater like the Polaris as your radiant heat source, I would consider a boiler like NYT Trinity or HTP Munchkin instead for your radiant heat source. Both will do a great job heating the place and saving you money by condensing and modulating their output.

Lastly, if you have scorched air as a backup, I would seriously stay away from the glycol in the water loops. In fact, you could institute a two stage-thermostat, where the hot air kicks in with a quick blast of hot air whenever it is needed.

Unknown

well

If you have one 3000 sq ft room, you might want to consider averaging or multiple zones. If the 3000 sq ft is simply the entire project size with a big room on one floor, then a single zone will be fine there.

Never put more than one room on a loop. Equal loop lengths are not important if you have balancing capabilities on your manifold. Leave yourself able to adjust output via balancing at least or adding zones later by isolating the rooms on their own loops.

You can do this with one pump, just calculate your pressure losses and flow rates to make sure you size it correctly. You are probably in the 6-7 GPM range at about 10 feet of head or so unless your manifold feeds are long or skinny. but calculate to be sure.

Definitely go with indoor and outdoor feedback. Your slab response times will improve dramatically without losing efficiency and you should gain efficiency that will pay back the cost of the controller easily.

also do not skimp on tubing. I would guess you have lots of marginal heating periods which means the system will be "off" a lot and then "on" again. Perhaps consider slab minimum temperature sensing, or tighten up the tubing install (especially around the perimeter) to let the slab react even faster.

Good luck! be glad you figured out what was up before you put in 3000' of non barrier pipe with a ferrous heat source!!!!

_______________________________

Northeast Radiant Technology, LLC

Robert Brown, Co-Owner, RPA certified Radiant Designer

207.899.2328
NRT@maine.rr.com