Would appreciate feedback.

nibs

We are building a new house with inslab 1/2 pex. Longest loop is 300' mostly around 9" o/c, the other 5 are between 200 & 300. Am experienced in construction both wearing the tools and in management, estimating and project management.
House is about 1200 sq ft on one level, 50% bermed, and has lots of thermal mass, interior walls are ferro cement etc. roof is r 50 or r 70, last winter we were able to keep the interior above freezing with a wood fireplace when outside temps were -10 C even tho the wall insulation is not complete. On a day that outside temps are 35+ the interior stays around 20 (70 F) with no A/C.
The slab is as follows Well drained sandy soil compacted Double layer poly 2" +/- of ground styrofoam entrained in concrete mix 1cement 2 sand 5 ground styro by volume. 3" foam 1/2 pex stapled or clipped in place.
2" concrete mix 1 cement 2 sand 2 crushed rock. no rebar or mesh, with fiber and super plasticizer for water reduction. because of age (we are in our 70's) we pour each loop in 2 pours 3 days apart which gives us control joints, Pex is sleeved at joints, we keep the latest pour wet for a week or ten days. by then we have prepped for the next pour. Because we are working so slowly we coil the pex needed to run to manifolds and keep it as protected as possible. until we pour the area of floor where it will run (kitchen & hallway etc). Each Pex loop is pressurized the day before we pour and is monitored until the day we need the gage for the next poor. So far no problems, tho reading the thread about the cement buggy made me laugh, we hand carry the cement in buckets so as to protect the pex, or we tip the mud from the mixer onto a piece of 5/8 plywood and rake it, mostly with a wood rake.
I calculate that we will need 35000 btus on a -20 deg day (we are very well insulated) I have gone into a bit too much detail because I have some questions and would like feedback.
I would like to use a modulating tankless water heater as boiler, the one I am looking at has a max output of 144000 btu's but will light at about 1/2 gpm. Will that be a good choice?
Layout is one large living room 25 X 35 a 16 x 14 bedroom an 8 x 9 spare bed/office, 8 x 9 bathroom and 8 x 9 utility room. Am thinking 2 zones one for the lving rm kitchen there is a fireplace on north side with a thermostat against the west wall which is 2X6 wood framed with large windows. The room has a clearstory with 6 3'X3' windows south facing. and the other zone bedrooms and bath, was thinking that two circulating pumps controlled by their thermostats would be the least expensive way of separating the zones, two manifolds on the pressure side and one manifold on the return side. Each loop to have a ball valve which may be used for balancing etc.
Cost is an extreme problem, we seem to run out of money long before we run out of month so are doing
95% of the work ourselves, and have been known to drive 600 miles to save money on insulation. My favorite wife did a rock wall over the fireplace, she does the cement mixing, we do hire a young lad to lift buckets into the mixer for her on pour days.
The feedback I seek is on the boiler, pumps, thermostats, zones.
Very fine site, this is my first post and really hope to get some hints, we have been building for 7 summers now and hope to move in next fall. 2019.

kcopp

What are your options for fuel?

ScottSecor

What is your location? Knowing it would give us an idea of weather, material availability, contractor availability (if ever needed), etc. Should we assume it will it be just you and your wife living in the house? Is electricity cheap or expensive?

As far as your heat loss calculations they seem about right. But please keep all of your design temp numbers in Fahrenheit for us dumb Americans, makes it easier for us to calculate.

nibs

Fuel options are Elec about $0.12/KW. Propane, NG, or wood. My preference was for wood, but my boss says schlepping wood in her 80's after I depart this mortal coil is not on, so we are going with NG.
Location is 100 miles North of Spokane just across the border.
Zone 4. Will edit the temperatures to show Fahrenheit asap.
Thank you for the responses.

hot_rod

I would have guessed a lower DD load on such a well insulated home? I've noticed on super insulated homes that you often do not have warm floors when loads are real low, be prepared.
Did you use a radiant specific load program, one that takes into account the berm?

I'm helping a friend with an identical size home, well insulated but not super insulated, not bermed in Whitefish Mt and the load came in under 30K

A tankless water heater is not a great choice for a hydronic appliance. I'd suggest a tank style to give you some buffering. HTP or Polaris are a couple brands.

Paul Pollets

grinding up styrofoam and mixing it in the slab pour will make the concrete less emissive. Is that what you're doing? Like Hot Rod said, stay away from a tankless and go with a modulating boiler and indirect DHW or try a combi unit, since your home is not that large. Doing the calcs on a radiant specific software will take all the guesswork out of the equation. The design temp for Salmo, BC is 18 degrees F.

nibs

What a resource, wish I had found you guys a year ago.
Sorry about using C, was going to edit to put in F equivalents but the system won't allow it.
I agree about the tankless drawbacks, her highness is adamant that we do not have room for a tank in the room which will also have washer dryer, and DWH, Elec panel etc.
Bob, are you saying we may have to open the door to get the floor warm? (Laughs)?
So far the only criticism is of the boiler type so I guess there is nothing too drastically wrong with our plan so far, (floor 60%) poured.
Thank you again for the feedback, was feeling a little lost.
Tony.

hot_rod

So a dual slab with foam between the lower and upper slab?

nibs

Yes and the lower slab has ground up styrofoam particles in it, this helps with insulation but has a lower compressive strength, makes a very good base for the foam. We call it styro crete and have used it quite a bit for insulating fill. We tape the vapor barrier and the foam butt joins.

hot_rod

The challenge continues to be finding a small enough boiler for homes like yours. 50,000BTU/ are available with turndown around 18,000, which is still large for your application most of the year.

Also 50K is too small to provide DHW instantly, most Combis are 110,000 or larger, fine for DHW but will short cycle constantly on a load load home like yours.

That is the main reason a tank style, or a buffer tank is used by the pros. Electric boilers can modulate across that wide output range, but operating costs may be higher.

Often times a stubby buffer can fit under a wall hung boiler for a footprint of maybe 3X2'.

GBart

Once you are sure of your fuel and your load calc THEN you can decide, it sounds like you might want to consider a Weil McLain Ultra, I really like them because they are modulating and you can pipe an indirect to it and tell the control what the btu firing rate is for the indirect and when called it will ramp up to that, then modulate for heating. For example the 80 ranges (input) from 16k btu/hr to 80k, next up 21k to 105, etc. so if you need 32k for heat and 95k for hot water you pick the 105 and it dials itself in.

https://www.weil-mclain.com/sites/default/files/field-file/WM Ultra Series 4 Boiler Brochure 0717.pdf

hot_rod

I'd double check that load number; if in fact design is around 18F as Paul mentioned, your number sound high. I've seen loads in buildings like that in low teens or single digits, BTU/ sq. ft

nibs

Because the house is bermed we feared that it would be dark, so have a cathedral roof over the living room that is 9' to 16' high and allows for lots of windows.
I have a tendency to over design, so when I did the loss calcs, I used conservative numbers, and was amazed to come up with a low number like 35K BTU's. You guys are telling me that my number is high. LOL, I have a lot to learn.

hot_rod

Just a guesstimate on my part, based on the earth berm and small square footage. Big glass would be a load consideration, of course.

If you go with a Combi boiler, your sizing will be based on the amount of DHW you need or want.

nibs

What would be the smallest buffer tank you would recommend, I have been thinking that way already?
BTW, when we pour the first 'styro crete' slab, we press the foam boards into the wet cement, and press it with weights to get a bond and full support. setting up to do that tomorrow.

hot_rod

Wow, you sound like a concrete slab over-achiver!

I think when you start looking at blank insulated buffer tanks, 30, 40, and 50 are the price point, smaller capacity tend to be more $$, less demand I suppose.

There are a number of brands of buffer and reverse indirect tanks built for that purpose. With small loads, an electric water heater can make a nice buffer tank also. I look for scratch and dent 20 and 30 gallons at suppliers

Here is my home system a 120 Lochinvar Nobel Combi with a 6 gallon buffer. i had enough real estate, but the tank could slide right in under the boiler. So heat, DHW and a buffer in a small space. It has a solar preheat component to the right.

Is your glass wall south facing? Passive gains need to be considered also, some sort of shading detail might be a good idea. Seems passive well insulated slab homes have more of an over-heating concern. We struggled with passive design homes in summer, keeping them cool and livable, and also mild sunny winter days they could overheat.

Sounds like you are doing your research.

nibs

So, based on information garnered here from the Mayor and others, I am building my own boiler, gonna put a 1/2 copper pipe with a candle underneath. Can anyone recommend a candle that will burn overnight????
No seriously though thanking all for their help, we are thinking about using a Takagi T-KJr2-IN-NG 6.6gpm 144K btu tankless,
coupled with two variable speed circulators, if we find we get short cycling we will add in a small buffer tank AKA electric water heater. We plan on having each circulator driving its own zone/manifold but using only one return manifold, comments please.

Zman

You are going to need to get the pressure drop of the heat exchanger in the Takagi in order to size your circulators. You may need to go primary/secondary.

Zman

It's pretty brutal. http://www.takagi.com/media/19489/TRGSS01613.pdf
I think primary/secondary with a boiler pump like a Taco 009 would be needed on the boiler side.

nibs

So with your help, and some discussion SWMBO (She who must be obeyed) has agreed to allow a tank type boiler for our space heating.
Would appreciate someone looking over my shoulder at my calculations being a howling neophyte in a forest of experts.
Based on a load requirement of 15000 btuh I estimate that we will need 1.5 gpm @ D20.
6 loops 300' max 1/2" pex = .3 gpm each.
rounded up for my conservative brain
= .19 psi per 100' or .57psi per 300' loop.
= 3.42 per 6 loops times 1.5 for fittings and bends 5.13 psi total.
= 12 ft head loss.
I make it that 1 Taco 7 or equal should be adequate.
Given that we can adjust the boiler output, and the pump DT to tune the set up. I almost shudder to ask if my numbers are within a sensible range.
Thank you.
Tony Aldridge AKA Nibs.

Ironman

I know I'm late to this party, but I would also highly recommend that you scrap the tankless water heater idea and go with a mod/con boiler. The tankless is not designed, controlled or approved for space heating and it will die a very early death if used that way. Then, you'll have to buy the boiler that you needed and have to pipe it in.

The tankless has a very high resistance to flow (head) that the small hydronic circs you're considering can't overcome. It's designed to have 60 psi coming in and an open faucet going out. Hydronic circs are designed for a 5 -7 psi drop.

A 20 gal buffer tank should be more than sufficient if you use a boiler in the 50 - 80k btu range. As hot rod stated, an electric tank water heater can be utilized.

HTP has a 20 gal S.S. buffer tank that's reasonably priced and I'd highly recommend their UFT boiler.

Here's a pic of one we did recently:

nibs

Ironman, my last post says we are going with a tank type, due to the advice we received here. The choice of tank has to be a function of cost/fitness for use.
My post asks that one of you experts, sprinkle holy water on my head loss calcs and size of circulator pump.
Thanks.

SuperJ

At 0.3gpm thru 300' of 1/2" pex what is your temp delta going to be? You might be out of heat before the end of the circuit leading to uneven heat distribution. Make sure you consider the temp delta when designing your tubing layout, some methods are more forgiving to high deltas.

Some sort of ECM pump would be a good choice, for efficiency and tuning flexibility.

nibs

Correct me if wrong please, an ECM pump modulates based on Delta T, so if it is seeing water that is too cold, it will speed up.
Also the delta T can be raised and lowered, as can the water temp from the tank. My 1/2" pex is at 9" centers in a very well insulated house with a lot of thermal mass.
I feel like a rank amateur here.
Thanks.

SuperJ

You can get Delta T ecm pumps that may or may not be appropriate for your job, but not all ECMs are delta T, in fact most commonly people use delta P (pressure), or multi-speed ECM pumps.

If it's piped counterflow spiral you will have alternating spacing of hotter and cooler piping that can help to negate the effect of high delta t for interior rooms. But sometime you can take advantage of the high delta to bias the heat where it's needed (against outside walls) without overheating the interior of the room. So one layout pattern isn't necessarily universally better than another.

Here is a mathy article on the subject.
https://www.pmengineer.com/articles/84671-pushing-the-circuit-length-envelope

Ironman

@nibs,
You only factor in the head loss of the longest loop plus the boiler, other piping, fittings, valves, etc. When calculating gpm, you factor all of the loops.

Gordy

I’m question why the styrofoam aggregate in your mix design? As @Paul Pollets pointed out it will hinder the heat transfer of the pex in the concrete.

Last time I saw ground styrofoam in concrete was an engineer who thought it would be a good mix design for a water craft competition. It didn’t work out so well.

nibs

Gordy, you are absolutely correct it would slow the heat transfer, Our slab consists of compacted sand, a VB then 2" +/- of sytrofoam 'crumbs' entrained in cement at a ratio of 1 cement, 2 sand, 5 styrofoam grindings, on the VB. Then we place 3" styrofoam boards into the wet 'styrocrete' and next day tape the styrofoam joins, the result at this point looks like the typical pex ready insulated surface.
Then we staple the pex onto the foam boards and cover with high strength cement at a mix design of 1 Cement, two sand, two washed 3/4"- gravel, adding fiber and super plasticizer to help with flowability. we add 20% fly ash if available, there is no styrofoam in the layer of cement that covers the pex.
We have been experimenting with 'styrocrete' for 6 years now, we estimate that it gives us an insulating non structural fill with about 2 R per inch, we have pavers and blocks made this way that have been in use for years, performing as expected. We love it it takes used styrofoam out of the waste stream and gives us a very useful material. for example our fireplace has a 1foot thick styrocrete wall behind a thin concrete wall, it slows the heat migrating outwards through the wall. Beneath the floor foam board it is easier to level than sand, adheres to the foam board, has a PSI that is much higher than the foam board and adds a little insulation at very low cost. The fact that the styrofoam crumbs take up a little water during the mixing makes the cement very hard as it allows more long chain molecules to form. One university study I read indicates that we can expect a lower PSI but about equal tensile strength to regular 3500 psi concrete.
You asked, but these days hydronic design for my house keeps me awake at night, I worry about pump sizes controls thermostats etc a whole new field for me. Too bad I am too old to ever be able to help others with their hydronics, but I can refer people to you folk.
Thank you,
Tony

Zman

You don't multiply the head.The resistance stays the same, only the flow increases.
You are going to have a hard time finding a circ for 2.1 feet of head and 1.8 gpm. Thats good news because a tighter delta will give you more even heat.
The 007 has a pretty flat curve for radiant.
The Grundfos 15-58 is an inexpensive versatile circ for radiant.
Speed 1 would give you about 4 gpm and 6.5 feet of head.

Solid_Fuel_Man

The Taco equivalent of the Grundfos 15-58 is the 0015. Both very well suited to residential sized radiant type of head and flows.

nibs

At the expense of sounding like the village idiot, if one uses a tank type gas boiler why not just leave an air space at the top of the tank for expansion?
It would be simple to fit a small tube onto the pressure relief valve to allow it to operate safely while maintaining such a gap.
Built a pair of simple fittings for my sailboat that allowed the space heater to thermosyphon hot water into a small electric HW tank while at sea.

Larry Weingarten

Hello, If it's a glass lined tank, allowing air to build up will prevent the anode rod from protecting the steel tank and it could rust out prematurely. In a stainless tank, it would be less of a problem

Yours, Larry

Alan (California Radiant) Forbes

This seems like the perfect job for a Rinnai e50C combi boiler. Load matches boiler output. Order it with the low-loss header to allow your micro zoning. I've installed two of them and have been very happy.

nibs

What a great site, thanking all here for their help.
Alan, if we can get the Utility company's rebate for the 50C it ha became the front runner. SWMBO loves that it takes up so little space for DHW and radiant.
The older model 50 had its own expansion tank, but if we are reading the tables correctly (always a problem) the newer model does not.
Your thoughts about the Rinnai 50C, and any info you can pass on would be appreciated.
Tony

Alan (California Radiant) Forbes

Here is a picture of the last one we installed and it did not come with an expansion tank.

You can see the low-loss header just below the boiler.

Just make sure you can get along with the 2.1 gpm max hot water flow rate. This one serves a 1-bathroom in-law unit. They have one of those 12" diameter overhead rain-style shower heads and there's plenty of hot water for it.

The connections at the boiler are very close together; fat fingers may be a problem.

Their installation instructions used to be really bad, but they are much better now. There are specific instructions on how to adjust your fuel mix. As with any new boiler installation, check it with a combustion analyzer and also check your gas pressure with a manometer. If you don't have one, find someone that does.