Posted By Dana1 on 22 Apr 2011 05:10 PM
And yet...

"Tekmar is certainly acceptable but one of the most expensive ways to gitter dunnnn."

...implies there's a less expensive way to get outdoor reset with a HW based heating system???

(There's no ROI to any of it, at Santa Cruz heating loads.)

I am finding this to be the painful truth. ROI seems to be out the window here - it is now CPQ Cost Per Quality equation - Under $20k

Hey, I just want to get a simple system that won't cost too much, is reliable, meets our modest heat load, and can be serviced by the locals - The last item remains a question as I keep being steered towards Navien and other systems by locals.

Items still pending seem to be:
1. Finding the right (read "good enough") condensing tank heater.
2. Low cost Outdoor reset control & manifold design
3. Balancing the system between all radiant in floor downstairs and the correct amount of upstairs radiant "baseboards"

Posted By Montysc on 25 Feb 2011 11:52 AM
I have better energy numbers from now.

What should I post?

Based on my reading it looks like heat load looks is aprox 35k
Upstairs 14k
Downstairs 21k

I just stumbled across what on first blush looks to be a pretty good downloadable heat loss estimation freebie from Crown Boiler, (which also has a handy tab with the 97.5% heating design temps for a gazillion locations in N. America. The design temp for Santa Cruz is 38F, as I had expected.)

http://www.crownboiler.com/Support/...ler-Sizing

http://www.crownboiler.com/docu...ulator.xls

(Not that the heating pros in your area ever get it wrong, but) it's worth entering the data carefully and seeing what it comes up with as a sanity check. 

I've yet to vet this tool out against measured reality or other vendors' tools, but it's surely way better than a WAG or a "...lessee, ya gots 2400-2500 feet times 18BTU/foot gets ya..."   type number. 

I'd still be  surprised if your house actually came in at 35KBTU/hr @ 38F, even with your relatively high glazed area fraction.

Posted By Dana1 on 05 May 2011 04:25 PM

Posted By Montysc on 25 Feb 2011 11:52 AM
I have better energy numbers from now.

What should I post?

Based on my reading it looks like heat load looks is aprox 35k
Upstairs 14k
Downstairs 21k

I just stumbled across what on first blush looks to be a pretty good downloadable heat loss estimation freebie from Crown Boiler, (which also has a handy tab with the 97.5% heating design temps for a gazillion locations in N. America. The design temp for Santa Cruz is 38F, as I had expected.)

http://www.crownboiler.com/Support/...ler-Sizing

http://www.crownboiler.com/docu...ulator.xls

(Not that the heating pros in your area ever get it wrong, but) it's worth entering the data carefully and seeing what it comes up with as a sanity check. 

I've yet to vet this tool out against measured reality or other vendors' tools, but it's surely way better than a WAG or a "...lessee, ya gots 2400-2500 feet times 18BTU/foot gets ya..."   type number. 

I'd still be  surprised if your house actually came in at 35KBTU/hr @ 38F, even with your relatively high glazed area fraction.

Dana,

I redid the heat loss calcs (using the included worksheets from the original calculations I have as they have all of the values for sq/ft U-vaules, Delta T and infiltration calcs all spelled out - So all I had to do was repalce some of the values and run the nubmer.  I used the the new 38F number you suggested (which creates a DeltaT of 32 with an Indoor Dry bulb of 70F).

Results:
Upstairs = 13,675 btu/hr total heat loss
Downstairs = 10,348K btu/hr total heat loss

With that in mind - it seems I could easily meet my upstairs heat load with 3 or 4 Runtal baseboard radiators 6" or 9" tall - I have room for 1 14ft one, 1 12ft one, and 1 13 ft one.

I do need to look at what type of outdoor reset I could run on the Polaris or equivalent condensing tank boiler if we choose that round.  However, with some of the savings gained by switching to baseboard radiators upstairs we could go with a Munchkin 80 combi-boiler and a 50gal indirect tank.  I got a quote some time ago for the pair and it was probably only $1k more than the Polaris would run with the heat exchanger and such...plus by the time I start adding things like outdoor resets and others it might be closer.

Installing an over-sized condensing boiler will have it bumping off it's minimum fire burning more fuel, getting less comfort and creating service problems by wearing out switches. Best to let a professional, experienced in such work, perform a proper heat load, specify the equipment and then find a good mechanic to install it accordingly.

In the long run you will get what you pay for.

With typical design heat loads under 30K the population of experience local hydronic design professionals who would take that much care & precision might be a bit thin. (Hot air gas & heat-pumps probably the dominate the space heating market in Santa Cruz.)

MA has it right - an un-buffered Munchkin-80 running w/outdoor reset would be well-oversized for the load and prone to short cycling at part load with low-temp-low-mass radiation. Even at min-mod the Munchkin T80 is almost 2x the design day load of your smaller zone, and the 80MR2's min-mod output is as much as your whole-house design condition heat load. But you could probably make it work OK with fixed-temp and bang/bang flow control. A condensing tank HW heater would be simple (and probably cheaper even with a pricey Tekmar outdoor reset mixer thrown in), and simply can't short-cycle no matter how low the load. The heating loads are simply too small to derive benefits from burner modulation, so you have to rely on buffering/storing BTUs in thermal mass x temperature hysteresis to provide sufficiently/efficiently long burn cycles and to minimize the number of burns. Tank type HW heaters are inherently self-buffered, with a minimum burn time pre-defined by it's burner output, it's water volume, and the hysteresis of it's controls. Adding small or intermittent loads can't reduce the burn time below the minimum, and larger loads just extend the burn time above the minimum. Bigger deal condensing HW tanki combi like the HTP Versa use mass/hysteresis, modulation, AND outdoor reset control, but that's way overkill for this situation.

In my last post I think I went a bit high on the Combi Boiler route.

I will talk with my heating contractor - but I do think we will look at a possibility50k combi boiler (not 80 as above) with an outdoor reset - also paired to a small indirect tank. I think that is a good option to compare against a condensing tank heater.

Are there other combi-boilers with a lower than 18,000 btuh low end fire like the Munckin 50

You are mistaken and ignoring Dana's rather succinct analysis. You may be better served by getting a Certified Designer from a cold climate to specify the equipment and have a good local mechanic install it.

Here in Minnesota we have quite a lot of experience (if not knowledge of) heating systems. In climates such as yours - and small or super insulated homes here- we often use combi water heating and space heating systems, using domestic water heaters suitable for both.

As your domestic hot water load outweighs the heating load, it makes sense to focus on the former. If you require, or desire, high efficiency, GREEN, quiet, gas-burning appliance, a condensing water heater is the answer. It is easier to design, install and pay for, will likely last longer in your application and operate at lower cost than a ModCon with an indirect (I can't believe I am writing this).

And keep in mind, I am the ModCon zealot.

I hope no one thinks I am ignoring anyone's advice! I have taken Dana's expert help and looked again at the heat load, which is quite a bit lower with the higher design day temp of 38 degrees.

I really appreciate everything each has provided. I was sold on the idea of the condensing water heater based on the conversations and advice here.

The contractors locally are trying to steer me elsewhere...so I am at least trying to figure out why.

I did ask if there were better alternatives to the Polaris in a earlier post, but didn't get any suggestions...

Navien, Noritz tankless or a cheap old school tank heater are what the locals are suggesting.

I think we eliminated the tankless at it clearly will not store heat for those micro-zones. Any condensing tank type water heater will due. No one that knows what they are doing will specify the system over the internet, but you can find people who will do it for you for a fee (in fact several have contributed to this thread).

From experience I can tell you that there is more than enough accurate information here to satisfy your stated goal.

The Navien combi's mid-mod is about the same as that of the Munchkin T50, and still 1.5x the output of your smaller zone's DESIGN DAY heat load, which makes it 3-4x oversized for the average. Min-mod on the smallest Noritz NH boiler is 55K, ~ 2x your whole house design day heat load, 10x your average whole house load. With your heat loads you'd need a boiler that modulates down to under ~5K (about half the design-day load of your smaller zone) to get much benefit out of burner modulation. Most of the hours of the heating season your binned hourly heat loads will be less than 25% of your design day load, and no condensing burners currently available modulate that low. (Which is why we're breaking Morgan's mod-con-lovin' heart with this discussion, :-) )

When you're running at temps where the radiation can deliver the output of the burner you're fine, BTUs out=BTUs in , and it runs until the thermostat is satisfied without cycling the burner.

But running outdoor reset, at part load you're running at temps where the radiation puts out substantially less heat into the room, which is fine from a comfort point of view, but the burner's output is hard-limited to it's low-end modulation. Running at a temp where BTUs out is LESS than BTUs in, the heating water temps rise until the hysteresis control in the boiler turns it off. That's also just fine, if the burn length is still reasonably long, but in an all low-mass situation like yours you'd have to be able to run a HUGE hysteresis to keep it from short-cycling.

For example: With 10F of hysteresis assuming 15KBTU/hr min-output and you've tweaked it all in so that it'll run at min-mod most of the time, assuming also~5 gallons of water in the boiler + zone (it's probably less), it only takes ~100 seconds to raise the water temp that 10F, and the burner trips of. In outdoor reset operation, assuming your running a water temp where the radiation is putting out 7.5K (half the design day load of your baseboard zone), that's only increased to ~200 seconds, which is still less than 3 minutes. No matter what, you're screwed. But if you insert 40 gallons of water as a buffering mass (for 45 gallons total) you're suddenly up to 15 minutes of minimum burn time at min-mod, or a half hour when the radiation taking 7500BTU/hr out of the system. You get the same amount of heat into the room in an hour on ONE BURN that would have taken 20 burns without the buffering mass. As the heat load and operating temp goes even lower with even less radiation output, the total number of burns goes up in the un-buffered system,

If you set it up with enough radiation such that either zone on it's own delivers the boiler's min-mod output to the room with with ~110F or 120F water you can probably run it just fine (and condensing) at a fixed low temp, no outdoor reset, and the T-stat's hysteresis & the thermal mass of the zone/house will determine burner run times rather than the system mass on it's own.

To run it with outdoor reset with an oversized burner, only solution is to have sufficient system mass to run efficiently at a modest temperature hysteresis. Neither the Navien, Noritz, or Munchkin has much mass in the boiler, and the mass in the Runtal is also pretty minimal (you'd get more out of cast-iron, but not necessarily enough.) In outdoor reset mode it'll short cycle- count on it! The thermal mass of radiant floors other than concrete or gypcrete slab-types is also pretty low. You need to buffer it.

Lapses of understanding of and dealing with these issues is not unique to the mild climates of northern CA- there are ample cases here in central MA (6500-7000 heating degree day climate, design temps in the +/- low single digits F.) It's even worse when the only fuel option is oil, where even the smallest boilers are 2x oversized for the whole house heat load, and the house has been divided in to 2-3-4 or more zones, and the radiation is all low mass. Systems with central buffers are rare, yet the mass of even a cast-iron boiler still isn't enough to keep them from short-cycling to death on zone calls. Yet these systems abound, running even the best triple-pass 87% AFUE boilers with outdoor reset controls at 60-65% as-used efficiency due to lack of appreciation of the whole-system design. Push the contractors for the approximate minimum burn-time number on the proposed installation after tweaking- if they can't calculate a range pretty quickly, (or look it up in their design notes) they haven't really done the design. If it's 5 minutes or less there are maintenance & efficiency issues in play. At 10+ minutes min-burn you needn't much worry- the efficiency won't get any higher with longer burns, and the cycling wear on equipment is pretty low.

As for other condensing tanks, IIRC I had recommended at least looking at the HTP Versa series. The Polaris is easy to design a system around, and less sophisticated/cheaper than the HTP Versa series (which are also easy to design a system around, but have their own outdoor reset control function, as well as fully modulating burners.) You can probably tweak a percent or three better efficiency out of a Versa, but it's likely to come in at something of a premium over a Polaris based system, (unless the system designer is a hack, not a designer.)

Posted By Dana1 on 09 May 2011 02:52 PM
The Navien combi's mid-mod is about the same as that of the Munchkin T50, and still 1.5x the output of your smaller zone's DESIGN DAY heat load, which makes it 3-4x oversized for the average. Min-mod on the smallest Noritz NH boiler is 55K, ~ 2x your whole house design day heat load, 10x your average whole house load. With your heat loads you'd need a boiler that modulates down to under ~5K (about half the design-day load of your smaller zone) to get much benefit out of burner modulation. Most of the hours of the heating season your binned hourly heat loads will be less than 25% of your design day load, and no condensing burners currently available modulate that low. (Which is why we're breaking Morgan's mod-con-lovin' heart with this discussion, :-) )

When you're running at temps where the radiation can deliver the output of the burner you're fine, BTUs out=BTUs in , and it runs until the thermostat is satisfied without cycling the burner.

But running outdoor reset, at part load you're running at temps where the radiation puts out substantially less heat into the room, which is fine from a comfort point of view, but the burner's output is hard-limited to it's low-end modulation. Running at a temp where BTUs out is LESS than BTUs in, the heating water temps rise until the hysteresis control in the boiler turns it off. That's also just fine, if the burn length is still reasonably long, but in an all low-mass situation like yours you'd have to be able to run a HUGE hysteresis to keep it from short-cycling.

For example: With 10F of hysteresis assuming 15KBTU/hr min-output and you've tweaked it all in so that it'll run at min-mod most of the time, assuming also~5 gallons of water in the boiler + zone (it's probably less), it only takes ~100 seconds to raise the water temp that 10F, and the burner trips of. In outdoor reset operation, assuming your running a water temp where the radiation is putting out 7.5K (half the design day load of your baseboard zone), that's only increased to ~200 seconds, which is still less than 3 minutes. No matter what, you're screwed. But if you insert 40 gallons of water as a buffering mass (for 45 gallons total) you're suddenly up to 15 minutes of minimum burn time at min-mod, or a half hour when the radiation taking 7500BTU/hr out of the system. You get the same amount of heat into the room in an hour on ONE BURN that would have taken 20 burns without the buffering mass. As the heat load and operating temp goes even lower with even less radiation output, the total number of burns goes up in the un-buffered system,

If you set it up with enough radiation such that either zone on it's own delivers the boiler's min-mod output to the room with with ~110F or 120F water you can probably run it just fine (and condensing) at a fixed low temp, no outdoor reset, and the T-stat's hysteresis & the thermal mass of the zone/house will determine burner run times rather than the system mass on it's own.

To run it with outdoor reset with an oversized burner, only solution is to have sufficient system mass to run efficiently at a modest temperature hysteresis. Neither the Navien, Noritz, or Munchkin has much mass in the boiler, and the mass in the Runtal is also pretty minimal (you'd get more out of cast-iron, but not necessarily enough.) In outdoor reset mode it'll short cycle- count on it! The thermal mass of radiant floors other than concrete or gypcrete slab-types is also pretty low. You need to buffer it.

Lapses of understanding of and dealing with these issues is not unique to the mild climates of northern CA- there are ample cases here in central MA (6500-7000 heating degree day climate, design temps in the +/- low single digits F.) It's even worse when the only fuel option is oil, where even the smallest boilers are 2x oversized for the whole house heat load, and the house has been divided in to 2-3-4 or more zones, and the radiation is all low mass. Systems with central buffers are rare, yet the mass of even a cast-iron boiler still isn't enough to keep them from short-cycling to death on zone calls. Yet these systems abound, running even the best triple-pass 87% AFUE boilers with outdoor reset controls at 60-65% as-used efficiency due to lack of appreciation of the whole-system design. Push the contractors for the approximate minimum burn-time number on the proposed installation after tweaking- if they can't calculate a range pretty quickly, (or look it up in their design notes) they haven't really done the design. If it's 5 minutes or less there are maintenance & efficiency issues in play. At 10+ minutes min-burn you needn't much worry- the efficiency won't get any higher with longer burns, and the cycling wear on equipment is pretty low.

As for other condensing tanks, IIRC I had recommended at least looking at the HTP Versa series. The Polaris is easy to design a system around, and less sophisticated/cheaper than the HTP Versa series (which are also easy to design a system around, but have their own outdoor reset control function, as well as fully modulating burners.) You can probably tweak a percent or three better efficiency out of a Versa, but it's likely to come in at something of a premium over a Polaris based system, (unless the system designer is a hack, not a designer.)

Thank you very much for the informative post Dana! I did take a look at the Versa-Hydro units when you posted about them before - they are way over our budget at $9K-10K.

I don't think I could approach that price with a Polaris and outdoor reset, valving, HX etc...

I guess I was looking for opinons on the pros/cons between the different "lower end" condensing tank heaters - the models I have found include the Polaris, Vertex, Phoenix etc...

Both the Polaris and Phoenix have been out there for awhile with decent track records in combi systems. The Vertex is fairly new, can't say whether it's better or worse than the others, but the setup for space heating with any of them is basically the same.

The Phoenix has a fully modulating burner with boiler-like turndown range with a ~35K min-mod, which differentiates it from the bang-bang burners of the Polaris & Vertex , but like the Polaris it lacks features like outdoor reset, which would still have to be done externally. You''ll get longer burns out of the Phoenix, but whether that's going to add up to a much more as-used efficiency in your case isn't a slam dunk, since even your design condition heat loads are still below the min-mod of the burner. The Versa series are basically the same technology, but with internal heat exchangers for isolating the heating system from the potable, but with much more sophisticated control.

Dana thanks again for your information!

We are finalizing our under slab insulation this week and I had to steer my GC away from the local "preferred" use of Insul-Tarp! Both the heating contractor and the local supplier of radiant heat products have suggested this!

Apparently everyone in the "know" here locally is in love with the stuff. Here in Nor Cal there is very little knowledge on the correct way to do radiant under slab it appears...As far as I can tell anyway.

I requested 1" XPS foam instead - we now have 1" pink fomular foam being laid down!

Based on advice from my Structural Engineer, and research here, I requested that the XPS foam be put down over the vapor barrier which is on top of the graded gravel layer.

My question is how much of a gap (if any) should be allowed between the foundation stem walls and the foam?

Right now based on my observation it looks like there is a 6"-9" gap between the slab and where the stem walls will form - I don't want to over think this, and with our mild climate it seems like we don't need to go up the foundation wall sides with the foam as would be required in other colder climates. Basically, the foam might not be extending all the way to the edge of the slab - but somewhat close to where the stem walls will end up being.

Man I feel Obsessive Compulsive - OCD!

The edge of slab is the most critical . More energy can be lost at this point than beneath slab. Yes you are probably over thinking job. Insulate at least a foot or more above grade.

Hello,
long post string here, stopping lateral heat loss is important.
Sad to say.... you are close on the foam, but the correct choice is 2 inch, and yes watch the edges.
Said another way;
Fill to 6 inches top of slab
6 mill plastic
2 inch foam
Snap with red chalk line your top slab height on perimeter for reference. Red is more durable than blue.
Contractor trick for edges; rip foam with table saw to 2"x 6" X 8' strips (45deg bevel top 2 inches if exposed edge) use the field 2 inch foam to press the 6 inch strip around the perimeter of the slab. Glue vertical 6 inch strip with cheep Dap acrylic caulk to help hold in place for pour.
Staple pex to foam
4 inch slab, wa la
Best to all,
Dan

You have done a great job! Blanket are for beds and are not use or specified by radiant floor heating professionals. It is a gimmick to make the labor cost go down at the expense of long-term efficiency.

The XPS covers slab under and edge and may sit on the foundation ledge and must go up to protect the edge from the outdoor temperature.

Well I found some pretty bad info about the blanket systems - seems like they would be only marginally better than zero insulation.

The slab and foundation edge are monolithic so there is no way to extend the foam all the way out to the edge of the slab - as it would isolate the slab from from the footings...

We don't have stem walls like I thought and there won't be any curb walls just a final concrete surface all at the same level - so no way to insulate the ends that I can see, beyond putting foam on the outside, which I don't think we would need here in Northern California...

We are ending the foam about 9-12" away from the outside finished edge as that is where the re-bar ties for the slab tie in to the rebar in the footings.

In climate zone 3   R5 under the slab is long-term cost effective even WITHOUT the radiant heating in the floor.  R10 is definitely cost-effective long term with radiant, even in a mild climate.

See table 0.2, p10: http://www.buildingscience.com/docu...mate-zones

Taking the R10 right up the stem walls  fully continuous with the sub-slab R10 also the right thing to do.  Even though the linked document specifies R7.5 for the slab edges, a heated slab would be quite a bit lossier than an unheated slab at the edge. They're recommending R10 on basement walls too, so consider the stem wall  just an extremely short basement, eh?

An alternative approach for the stem walls would be to use insulated concrete forms for the stem walls, which will have at a minimum R8 inside, R8 on the exterior, and running the sub-slab foam right up to the inner stem-wall EPS.

Bubble pack roll products may run a high as R2 when tested in a ASTM C 518 test plate, but that will drop to less than R0.5 after a couple of years under a real-world slab.

I must have been typing while you were posting...

You DEFINITELY need to insulate all the way to the exterior edge in N.Cal (or even SoCal- see the table referred to in the previous post). The compressive strength of XPS is sufficient under-footing insulation on timber-frame walls (and even 10strooy concrete.) If the engineer/contractor/inspector doesn't want to do the math and balks, make the footings 6" wider for more surface area to float on.

Every break in the insulation is a thermal bridge to either the earth or the exterior air, and the outer foot or so' of the perimeter essentially IS the exterior, from a weekly-average temp point of view. A foot of dry dirt is still less than R2, wet dirt, less than R1. Building a decently insulated house and leaving a big heat leak at the bottom would be a mistake, since retrofitting at the bottom can be prohibitive. Only in places as warm as south Florida would insulating the slab or slab edge prove not-cost-effective in a 25 year present-value analysis. In NoCal it's cost effective in shorter years than that.