Hydronic Floor Heating System

[sailawayrb]

While designing the subject system for our new home, I came across this website:

http://www.pexuniverse.com/

I was very pleasantly surprised to learn that the components are relatively affordable and I expect to DIY our 1700 SF place for under $5K.  The most expensive item is the condensing boiler for about $3K.

I have calculated that our annual home BTU heat loss will be 46 million BTU's (R29 walls, R49 ceiling and Medford OR climate).  The house passive solar design will provide 25 million of these BTU's (about 55% of our total heating requirements).  When we are home, the 90+% efficient masonry heater will backup the passive solar design and provide the BTU difference.  When we are away, the hydronic floor heating system will backup the passive solar design and provide the BTU difference.  The hydronic floor heating system will also be used during the winter months to keep the floors in most rooms at a comfortable temperature and to keep the bathroom floors nice and warm.  Since the required hydronic floor heating system water supply temperature is only 94 deg F, I can use a condensing boiler that is 95+% efficient (the exhaust temperature is so low that standard PVC can be used).  Either the masonry heater OR the hydronic floor heating system is each fully capable of providing 100% of our total daily/monthly heating requirements, if necessary.

I have attached the Excel spreadsheet that I developed to perform the necessary calculations should someone here have a similar interest.  The hydronic floor heating calculations are based on the information from John Siegenthaler's "Modern Hydronic Heating".  The passive solar calculations are based on the information from Edward Mazria's "The Passive Solar Energy Book Expanded Professional Edition".  The solar celestial calculations used to design roof overhang and corresponding south glass solar exposure are from NOAA.  The masonry heater calculations are elementary and can easily be derived.  

Bob B.

[Lloyd]

Hi Bob,

Good job, the pex is a great product...may as well do all your plumbing while your at it. My project was on a scale smaller, but the pex for both hydroinc and domestic water was easy and 9 years later not one single issue.

Check out this link it's right up your alley and perfect timing for your project; http://www.atkinsonelectronics.com/energy/pdf/openhousebulletin.pdf Also look at thier product range, you will find everything you need for automation and control http://www.atkinsonelectronics.com

And this link to their HW SyS http://www.atkinsondemo.com/ord?file:^px/HotWater2.px
Lloyd

[sailawayrb]

Thanks for the positive feedback and the links Lloyd.  Yes, we will be using pex for the domestic water too.  Since our water is also from a well, it wouldn't make much sense to use anything else these days...especially since we already used about 800 feet of pex to get from the bottom of our well to the homesite.  

I drafted the preliminary hydronic control law, which will be PID using slab temps, room air temps, outdoor air temp, solar radiation (pyranometer), day of the year, and hour of the day as feedback.  Been using Mathlab/Simulink to evaluate the control law, but I haven't considered/selected H/W yet since it will be a few years before I tackle this.  My focus now is to make sure that I get everything in the slab design and construction drawings that I will eventually need later.

Bob B.

[sailawayrb]

Updated and attached a much improved version of this Excel spreadsheet.

Cheers,
Bob B.

[Tom Reed]

Hi Bob, how's your system coming? We use a listeroid to heat our light weight concrete floor and the heat is fantastic!

[sailawayrb]

Hi Tom,

I'm envious, my system is still very much in the design phase and I won't get to enjoy the joy for some time...

Last year was spent getting the well to home site and getting the hydro ram pump irrigation up and running.  The house and garage/shop(with guest quarters) design is done, but I need to transform it into actual construction drawings.  The new septic for the new place gets constructed in June.  Permitted it as a "repair" to 45 year-old existing septic even though the new tank and field will be quarter mile away from the existing system...big permit savings there and also avoids hassle/expensive of needing a sand filter system.  

Made a last hour decision to go with ICF walls in lieu of 2x6 construction.  I was surprised how affordable ICF has become.  I estimate about $15K for each building if DYI or $20K if subcontract out.  The ICF structural design (for seismic loading requirements and to address unique passive solar design aspects not in prescriptive building code) is nearing completion.  I will still put real cedar log siding on exterior which will result in the walls being about 15" thick.  The roof structure will be cantilevered trusses (48" overhang) with a 24" heel and this design was just completed this week.  As soon as new septic is done, I will submit everything to the county planners so I can show I am just hooking up to an existing septic that already meets the bedroom requirements for new place and that I am just replacing the existing mobile home with a new house so as to retain existing desirable setback from creek.  My plan is to build the garage/shop next summer and build the house a couple years later when I retire.  I also need to build the hydro electric plant in the next 5 years too assuming none of this doesn't kill me first...

Bob B.

[Tom Reed]

Sounds like you are moving along. It took me about 2 years to get our water system and once that was done things moved fast.

We used ICF's for the construction of our daylight basement. Having done it I would now do the whole house with it. Just be careful using the vibrator.

[sailawayrb]

Right, avoiding concrete voids is important...and I wish the Indians did a better job with that on our cast iron...  Glad to hear you are an ICF fan and enjoying your warm floor!  I hear about 18% of new construction in the states is now ICF.  Europe has been doing ICF and hydronic floor heat for a long time.

Bob

[sailawayrb]

Updated to incorporate some refinements and reflect estimated fuel usage.

Cheers,
Bob B.