Need help designing a system to heat my wood shop

barnstar

Hello to all.
I have a shop building that is 1000 sf, put 1/2 inch pex into the 4" concrete slab with xps foam underneath, four circuits at about 240' per loop. I have built the entire building myself, carpentry is my strongest but I have done it all from footer to the roof, including laying utilities into the building (h2o lines and 100 amp service line), also designed and put down the tubing in floor and finished the concrete slab (with a little help from pro finisher neighbor). I am now at the point where the building has insulation but the floor is not hooked up yet, so I would like to design a very basic RH system... seems I could do it myself if it's a simple system, with a little advice from someone more experienced in RH systems. I have done some homework already, but need a bit of guidance in my selection of the components.

so I am at square one, I need to select a heat source to run the hot water for the floor. I would like the boiler/heater unit to be propane and have two in my possession already: a Crown conventional boiler (BWF162), and also a BW propane 50 gallon tank heater. I am aware that the simplest system would prob utilize a tankless heater, I got the Crown boiler for a sweet deal and its new, was hooked up for a week and taken out by a contractor, but at the time I got it I hadn't done much homework yet other than figuring out how to insulate the slab and layout the tubing, so prob not the easiest source to install but it's what I have already so I'd like to use it if possible. I was told it would work fine for my application just need some way to lower the temp into the slab, that a mixing valve will do this (also realize that I'll need to raise the temp of return h2o to protect the boiler. I bought the BW tank heater for my house but ended up not using it, so I have that available also.

I have spent more than a few hours googling diagrams and reading threads in forums, in order to see if I could determine the proper way to install the conventional boiler. many different ways to skin the cat, as they say... but I came up with a system including a primary loop off the boiler, two closely spaced T's (one hot off boiler loop/ one cold return, upstream) off of that into a secondary loop which has mixing valve, feeds the manifold to the floor, a circulator on each loop and of course somewhere in there need a pressure tank, PRV, temp gauge for boiler return and also one ahead of the supply manifold, some shut offs and drains etc. but I suppose I am getting a bit ahead of myself here... get back to all that later, IF it applies. really what I'd like to know is, would I be better off getting rid of the boiler and getting a tankless heater to supply the system? If it's not unheard of and foolish to run a conventional boiler I'd like to stick with that... but I'm not opposed to going with a tankless (or the BW tank heater) if that makes more sense. My building has four circuits which will all run at the same temp, and it's a shop so my objective is to keep the building just warm enough to be able to work and keep pipes from freezing during the winter. I'm trying to do this at a low cost, this is not going to be a state of the art system with zone controllers or anything too technical.

If anyone here can steer me in the right direction, I am trying to first determine the right heat source and if my conventional boiler is ok to use, is it the right size (162k BTU) for my system? I am planning to get some professional help to consult with once the system is put together and it's time to start charging the system and running h20 thru the floor, purging the air out etc. I also have a friend who renovates houses who has offered to help me design the system, he has some experience in radiant and has built several systems for small homes. In addition to the boiler question, I was also hoping to hear some suggestions on circulators (what size motor/GPM etc.) and mixing valves if applicable and on what temperatures I should be running into the floor, back to the boiler, etc. I am the DIY guy here not a working pro, so I won't be offended by any suggestions on all the basics, I appreciate any help you all can give.

SWEI

First things first -- you need a heat loss calc for the building. Unless you live in Port Barrow or someplace similar, that figure will be under 30,000 BTUs/hr -- on the coldest day of the year. The other 97.5% of the time, you will need less. For a number of reasons, oversizing a heating boiler is a very bad idea.

What are your rates for LPG and electricity like?

barnstar

Okay, thanks for the input SWEI, you're absolutely right I should have started there... "first things first" as you stated. Totaled all the square footages of my building's walls, doors and windows etc. and the HLC I came up with was 37,522 BTU per hour. I get that radiant floor systems are complicated and require specific info. on the building specs to operate efficiently, and equipment (esp. the heat plant) must be sized properly. I had talked to a professional service/radiant products dealer before I bought my boiler asked questions about boiler output/size but HLC was never mentioned, now wishing I had discovered that info. before I bought the "good deal" boiler. The boiler in question is a conventional boiler @ .82 efficiency x 162,000 btu input= approx. 133,000 btu/hr. heating capacity, way oversized so I suppose I will be getting rid of it, and looking to get an LP gas tankless heater as those are more efficient than electric ones... is that correct?

Here's more detailed info. on my project:
1. the building's interior space is approximately 925 sq. ft.
2. concrete is 4" thick, entire floor is insulated with 2" thick XPS foam (perimeter of foundation too).
3. pex tubing is 1/2" oxygen barrier, spaced 12" OC, direct runs from manifold go to the perimeters, there are 4 circuits each one is approx. 230 ft. in length.
4. I live in SE PA, where lowest average temps are in the single digits, so my if my ODT is 5 degrees and my IDT is about 60-65 (shop building don't need it much warmer) I have a TD of 60 degrees.
5. 2x6 walls are insulated to R21 w/ vapor barrier, tight build with attention to detail
6. ceiling is insulated with 3" poly-iso (not sure but I think that equals an R value of 14-15) * I should note that the ceiling is high, top of wall is 12' and the peak is around 19-20', approximately 25 x 25 room with cathedral style ceiling, remaining 12' of the bldg. has a loft/ 9' ceiling. the building is a "story and a half" like a small barn... not sure if this ceiling issue will affect my HLC?

I am going to reconsider my heat plant and get some info. on propane fired tankless heaters, probably a somewhat easier system to design/build than what I was going at. To answer your question, my current electric rate is about 8 c. per kw... and propane is cheap and available where I live. If anyone reading this can help out, point me to any good literature/ links on size/ capacity of heaters, also need to figure out circulators/ flow rates and what supply and return temps. are needed for my system? I am willing to do any necessary homework, if it means this gets done right the first time around.

I might have said it earlier but this is a wood shop, I am just looking to keep the inside temp constant at around 60 degrees. It's very hard on equipment in the early/ late winter periods when temps swing from day to night and it makes condensation happen to machine tops. I have to work on the building when I don't have deadlines for my ww clients, so it's taken me several years to get to this point but it's been very rewarding to see the building take shape. I have been working in unheated space for the last 11 winters (my previous shop was a shack!) so hooking up this system is going to be dream like, I'll be able to carry on thru winter with more productivity. I appreciate any help. Ben

SWEI

Radiant wood shops rock!

What indoor space temp did your heat loss calc assume? Most default to something like 65°F or 68°F.

In order to control that floor, you're going to need to vary the water temp going to it using outdoor reset and constant circulation. With the boiler you have, that will require a second pump, a motorized mixing valve, and probably a buffer tank.

A small electric boiler would cost less brand new. So, what are your prices for electric and LPG like?

barnstar

I forgot to mention previously, but I have embedded an 8' section of tubing in the floor for a slab temp sensor... and here's some photos of my wood shop.

barnstar

The boiler I originally planned to use was a bargain but I'm not set on using it, I could resell it and go with something else if that's a better plan. Would I still need the motorized mixing valve and auxiliary tank if I switch to a system that runs off a tankless heater rather than a boiler? you said I'll need constant circulation and varying water temp, does that remain true if I were to switch to a different heat source? Is a tankless heater going to be able to keep up with demand from my system?

my electricity is at roughly 8 cents per KWH reasonable rate I have it locked for next 6 years. propane is very affordable and available in my area. what do you mean by small electric boiler?

SWEI

Any tankless water heater (regardless of fuel) would still need the second circ, mixing valve, and a buffer tank. They're neither designed nor warranteed (much) for the application.

Thermolec makes the smallest electric boilers I know of with built-in ODR control The B-11TMB should work for your load.
http://www.thermolec.com/en/productview.aspx?type=product&id=62

barnstar

OK, I'll take all this into consideration... ODR and a buffer tank seem like a good idea. The system is going to be a bit more complex than I had anticipated but it makes sense if the system is going to circulate constantly it will need to have extra hot water on reserve. Thanks again for the input.

Rich_49

Swei's idea of an electric boiler makes sense if the rates math out . Sell the boiler you have and if you have to use something you already have use the water heater . 37.5 BTU sq ft seems awfully high for the mid atlantic region considering the Wall R values you state . My bet is that it is more like 20- 25 BTU per sq ft . How did you perform the heat loss or whose calculator did you use ?
Remember also that as you go thicker with PolyIso the Rvalue per inch changes for the better .

http://c.ymcdn.com/sites/www.polyiso.org/resource/resmgr/Technical_Bulletins/PB_PIMA_PerformanceBulletin_.pdf

You can really leverage the mass in that water heater and if you purchase an outdoor reset mixing valve you will have a hell of a system for a shop . A modulating / condensing water heater would be best though . That type unit allows you to set up tank differentials to hold out the burner till it makes most sense and the heat exchanger is much more efficient than any run of the mill water heater .

barnstar

Hi Rich, I had used a HLC from USboiler's website... so I backed up and refigured with new value for ceiling insul and a few other minor changes (reassessed the quality of my windows) and came up with a HLC of 27,320 btu/hour, which is closer to the 25 btu/ square foot figure.

At this point I am convinced that the way to go for heat source is a hot water heater since they are designed to make the lower temp needed for RFH and can withstand a lower temp return. Going to look at condensing heaters if I can afford one of those I will sell both my other units and get one of those. If not then I think I will be using the BW heater (50 gallon, rated at 36,000 btu input). going to be doing some more research over the next few days on water heaters, both tankless and tank ones, will also look into the ODR idea. Thanks for the response and the advice.

hot_rod

Just be careful trying to run a traditional water heater at low temperatures constantly, they need to heat up enough to dry out the venting at least.

If you hear dripping and hissing inside them as they run, it's running too cold, below the dew point of the fuel. It will eventually corrode away the burner and flue piping. I'd guess mid 70 to low 80% from a standard water heater.

A condensing appliance at typical slab SWT would get you 90+% efficiency and not have issues running at low returns.

Rich_49

Here's what you need . No need to worry about the things hot rod mentions either .
http://www.htproducts.com/phoenixldwaterheater.html

Mark Eatherton

Rich said:

Here's what you need . No need to worry about the things hot rod mentions either .
http://www.htproducts.com/phoenixldwaterheater.html

I think what Rich is saying is that with the HTP product, what HR says doesn't need to be worried about. Feel free to correct me if I am wrong Rich.

The common misconception that water heaters are good for low temperature operation is a fallacy. I had a 40 gallon WH as my heat source back in 2000 (Y2K compliant system...) When I finally got tired of hearing the water heater running full bore even when it was tepid outside, I replaced it with a real modcon boiler. My fuel use dropped 30%. Upon inspection of the flue, it was in terrible shape, and had been exposed to long term condensation in the upper parts of the flue that never caused it to drip down on the burner. It took vise grips and a hammer to get the flue baffle out of the heater...

As HR pointed out, these devices are NOT meant to condense long term, which when coupled to a high mass system they most probably WILL condense, even if you don't hear it, and WILL have a significantly shorter life expectancy. They are considered a "throw away" heat source, because you will most probably be throwing it away in 7 to 10 years, or less.

As has also been previously noted, the use of a DHW tankless heater, will also have "issues" due to misapplication. It was intended for a fixed flow with a large differential in temperature between inlet and outlet. When misapplied as a heating appliance, it short cycles, and never really gets hot enough to dry out the heat exchanger, and will also have s short life expectancy with a lot of problems when it does work.

What appears to be a cheap energy source will cost a lot more than a properly applied product in the life cycle costs. Maintenance, fuel consumption and short life expectancy will consume any potential savings in the initial investment.

Do yourself a favor, and spend the extra money to do it right the first time, and you won't regret it. If you opt for the lesser alternative, this conversation IS going to come back to haunt you eventually... And don't forget to have it maintained on a regular basis. Maintenance is required, not optional, unless you feel the need to violate your manufacturers warranty.

ME

barnstar

HR, Rich and Mark-
thank you all for taking the time to write, I really appreciate and value your input, it has been great help to me in planning the design of my shop's RH system. I may have to wait until my tax return comes in Feb. to afford the cost of a mod con water heater, but it seems like the right component to purchase when you consider the long term costs, environmental impacts and reliability of the system.
regards, Ben

Harvey Ramer

Modcon on a slab can easily attain 96% to 98% efficiency when properly set up.

SWEI

At 8 cents per kWH (unless you have NG available) you really should give serious consideration to a small electric boiler. Cost should be roughly 1/3rd of what you would spend on a quality mod/con.