Extremely Low-Load House

Mike T., Swampeast MO

<8 btu/hr sq.ft. loss @ -20F design temp.

Total lloss about 19 mbh for two floors of about 2,400 sq.ft. Ten rooms (three are baths and one of these rooms is combined entry/family/kitchen/dining that takes up about 2/3 of the ground floor.

One choice of emitters is <A href="http://www.mysoninc.com/mysPDFs/Decor_Tech_04.pdf">Myson Decor series H-11 two-tube</A>. Only about 64' of the baseboard which is already "oversized" compared to another suggestion of about 52'. <I>Approximately 300' of exterior walls on the 2 main floors.</I>

Homeowner desires TRVs and true constant circulation.

With a Manual-J loss in the neighborhood of 19mbh (5.6 kwh) <I>and expected heat load at design conditions of 12 mbh (3.5 kwh) or less</I>, I'm not seeing any well-suited mod-con.

Am <I>heavily</I> leaning towards a Bradford-White "water heater" with built-in space heating coil. While efficiency is certainly less than a mod con, I see the Bradford-White operating under nearly ideal circumstances (even the smallest model stores over 1 hour of heat at design conditions with 30F delta-t in the tank). Meanwhile I see any mod-con severely short-cycling in most weather with the emitters barely capable of absorbing MINIMIM boiler output at MAXIMUM temperature... With reset curves typical for baseboard I'm seeing < 6 mbh (1.75 kwh) output potential for the baseboard for at least 50% of their nine-month heating season. Just can't imagine <I>any</I> available mod-con being very happy driving such a system.

Suggestions please. I don't care how wild. As always, budget is a factor. Original budget based on the Myson Decor b/b and a Buderus GB.

Energy efficiency is a HIGH factor in design, but have serious doubts that a mod-con could operate near peak efficiency in this system.

As I've explained to the homeowner, it seems to me that he has produced a shell of such high efficiency and low load that trying to adapt a conventional (but "high efficiency") heat source is rather like chasing efficiency windmills with the added cost and complexity far greater than could ever be achieved.

Perry_3

Perfect application for geothermal hot water (with 120 Max water temp). Be sure that radiation is designed for 110 F water on a design heating day (so that it can handle the rare colder weather), be sure that compressor unit and HX is slighly oversized, and be really sure that the underground coil design is adequtely spaced with some extra capacity.

Perry

Unknown

buffer tank?

Mike T., Swampeast MO

Homeowner has not mentioned geo. VERY little time as they expect to move in within two months. Suspect that no experienced contractor could be found that that system material costs would rise multiple times. He did however mention that their electricity is extremely expensive and did not even want to use electricity for electric radiant floors in the baths.

Wayco Wayne_2

If not Geo thermal heat pump

then why not an air to water heat pump. Put a wind generator to make up the back up electricity. Hot Dam! WW

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Mike T., Swampeast MO

A buffer tank was my initial thought as well, but with constant circulation, TRVs and very low water content in the system it goes back to the problem of properly controlling that buffer such that it can be both a heat source AND a collector for heat. If I merely used a tank in series with the system it would effectively disappear once the system is maintaining space temperature.

Best ways I see to use a buffer here:

1) Use a single-coil "indirect" as the buffer tank. Minimum tank temp 120F or so. Second indirect required for DHW. At least this would work easily with readily available controls.

2) Use a dual-coil "indirect" as both buffer and DHW. Water in the tank for DHW; upper coil for space heating; lower coil for heating the tank. Again, minimum tank temp 120F or so. Since the boiler would only "think" it's supplying DHW, it would take some special control work to automatically increase tank temperature as the weather gets colder.

-----------------------------------------------

If the Bradford-White is used, I see an extremely simple system. One circulator. One differential pressure bypass valve. One warm-weather shutdown control. Two pairs of manifolds. No reset, no mixing valve(s), no thermostats--just TRVs.

Only drawback I see regarding control is that some manual adjustment (say 2 increases and 2 decreases per year) of the storage temperature dial would be desirable to reduce stand-by losses. If "set and forget" adjustment on the Bradford-White would suggest a motorized, reset-controlled mixing valve.

Mike T., Swampeast MO

Climate is FAR too cold for a traditional heat pump. See these average temperatures

Perry_3

The cost of the electicity is almost moot for Geothermal

A good geothermal system will cost about 1/5 in electricity what natuarl gas or oil based heat will cost.

All the electricity is being used for is moving the heat - not generating it.

As for timming: Look for geothermal contractors in your region (often they do jobs in a several hundred mile radius). Once installed, a local refridgeration service company can usually handle any maintenance (when I was looking at geothermal - I was going to pair the geothermal contractor from half way across the state with a local heating contractor; but I need 140 F water which is beyond normal geothermal equipment).

Perry

Nick S

Bradford White

I would think the Combicore would be fine. If you are looking for something similar but better (more expensive) you could go with a HTP Phoenix. I have never used one, but it seems like a good unit.

Unknown

Cripes, Mike. Check your degree days. 19k Sounds low, and it is, but efficiency in the heat source is certainly worthwhile up there. That's something like 9500 to 10,000 degree days a year up there. I have a hard time thinking you won't see payback if you get the efficiency up.

Run the boiler on ODR, maintaining a buffer tank with a 20 degree differential or something to leverage the mass of the tank. perhaps not perfectly ideal but still far better than a water heater.

Mike T., Swampeast MO

Yes, I know that 19mbh is EXTREMELY low for 2,400 sq.ft. in that climate. Others however have arrived at similar loss figures while with some saying "there's no way a house that size here can have losses that low."

I've used conventional triple-glazed windows for computation when in fact these are triple-glazed extremely low u "super windows" that the homeowner could only find in Canada. 12" thick R-50 walls. Double 2x6s with minimal thermal bridging (e.g. staggered studs wherever possible.) Rigid insulation plus "insulating" siding on the outside.

R-70 ceilings.

No attached garage. "Normal" door for access behind an enclosed "entry" area built external to the shell itself.

Know you can't compute for occupancy gains with regards to heat loss, but that doesn't mean I can't attempt to compensate for such regarding the actual heat requirement. Looks to me that even an "energy star" refrigerator would provide the majority of the requirement for the kitchen proper in nearly any weather.

There are a couple small baths that I seriously believe could be "overheated" in their version of "summer" with compact fluorescent lighting!

Unknown

You're missing what I'm saying.

Yes, 19k is low, but it's not THAT low, when you have that many degree days.

Put it this way: 19k in Texas vs 19k in northern maine. In Texas, who cares what you use for a heat source. In Northern Maine, you care. Even at 19k. Do a degree day fuel usage estimate and you should see what I mean. It may not need that much heat at any one time, but it needs it ALL THE TIME... so don't too glibly just throw a water heater at this thinking it doesn't matter, like the case would be in virginia or or something. It may not be huge, you are screwing yourself difference, but the mod/con buffer strategy should have payback if your numbers are in the ballpark.

Don't start second guessing your numbers and justifying heat source selection on "fuzzy" justifications. Run the numbers for real, then decide where you are at. Why, for instance, are you not using the real performance of the windows? If that knocks you down even further, ok, maybe the water heater makes sense. But at least run the numbers and see.

Mike T., Swampeast MO

Thanks Nick for suggesting the HTP Phoenix!

At least the minimum input rate of about 55 mbh is reasonable and very similar to the Bradford-White. s/s construction should give much longer service life and the system can still be extremely simple.

Mike T., Swampeast MO

Only problem I find with the Phoenix is the design of the HX coil for space heating. Not only is it confined to the bottom of the tank, but it is corrugated thus inviting to scale. While there's a tiny circulator to move the water in the tank itself, I believe the true capacity of the buffer will prove far less than the actual capacity of the tank.

The Bradford-White on the other hand has a large diameter, smooth HX coil running around the tank from nearly the top to the bottom. With nearly the same actual capacity I believe the true capacity of its buffer will be significantly larger.

Mike T., Swampeast MO

Not "my" region. I'm in SE Missouri. This job is in extreme northern Maine.

Mike T., Swampeast MO

Rob,

I'm giving the HIGHEST possible consideration to the heat source. Just spoke with one of my mentors (who has used both the Bradford White and a Phoenix--not to mention nearly every mod-con) and we both arrived at the conclusion that currently available mod-cons are not well-suited and that the design and output of the Bradford-White "Energy Saver" DH1-75S6BN make it the most suitable heat source.

"Siggy Software" shows less than $100/year fuel savings (with L.P. at $1.80/gallon) when comparing the Bradford-White to a condensing heat source. With about 28mbh of emitter output capability at 150F average water temp no mod-con I'm aware of would do much modulating except via a buffer. This agrees fairly closely with my annual fuel consumption estimate of the heat source ONLY for space heating where I included some occupancy gains.

This mentor also agreed that given the two general emitter choices (6" Myson Decor b/b) or horizontal Runtals (most about 8" wide x 6' tall) and considering the climate that reset is virtually unneeded as 140+ supply temperatures will be needed 6+ months of the year with 160 or so desirable for their brutal months. While I suspect that 110F average panel temperature will meet the design heat requirement (not heat loss), the system will truly need a decent sized reservoir of heat available for unusual weather conditions or occupant desire. If reset curves anywhere near typical for emitters of this design were used, response to a call to increase heat in even a single room would be extremely sluggish even in moderate weather.

Am using HVAC-Calc for computation. It does not include constructions for a home like this and I have had to interpolate some data. I can't consider such to be "fuzzy" justification. Even Siggy Software where you can "build" walls can't handle this some of this construction.

Unknown

Sounds good mike, then I would be interested in the assumptions on that figure, because I find it hard to believe that a water heater with 80% combustion efficiency (then, subtracted for the chimney effect of the tube in the tank) stacks up to even a cycling mod/con.

Further, by what rationale is "reset virtually unneeded" with design temps that high? The higher the design temp, the more useful reset is, isn't it? I could see if you were maxing out at 140 and using a conventional boiler that can't go lower than that, but even in that case I'm starting to look at mixing even for high temp emitters.. they can put out heat at lower temps, if you can give it to them after all. And as you well know.

So if your temps are really that high, and THIS system doesn't need ODR, then what system ever does??

You have a crazy envelope here. Why are you concerned with response time? you have a low load at any one time.. that means a small amount of energy will change the temperature of the space. This is the home LEAST worried about reset curves limiting response, short of high-mass wall homes.

right? or is this a weekend home?

I'm not trying to trash you Mike, just hashing it out for fun, but I'm not following the design logic here at all. which might be my failing, of course!

Mike T., Swampeast MO

Rob,

Believe me--I GREATLY appreciate yours (and others) input.

I agree that this is a "crazy envelope". He's even doubled ALL of the interior drywall for additional thermal mass!

I CERTAINLY won't say that a "water heater" at 80% combustion efficiency could EVER stack up to a mod-con but I just don't see the need for thousands of dollars of additional equipment (not to mention installation labor) costs in attempt to save a relatively tiny amount of fuel. The envelope itself is the TRUE fuel savings...

Some day we MIGHT get small mod-cons here in the U.S. When that happens one could easily be dropped into this system with nothing removed and [possibly] nothing added with little more labor than merely replacing the "water heater".

Why am I concerned with "response time"? I'm not joking that the opening of the front door (not the normal entry door) of this home in cold, windy weather is truly a significant event! I want INSTANTLY available water temperature suitable to get convection "cooking" when/if the need arises. I genuinely suspect that even a moderately tight reset curve in this situation would result in unacceptably sluggish response without manual adjustment.

My initial design idea--even after I arrived at the Bradford-White as the most suitable heat source--included a motorized, reset controlled mixing valve. Once the ENTIRE system was in my head, I saw such as little more than needless complication and expense. My mentor who has lived in a designed systems for cold climates completely agrees that reset has little meaning for this system.

Not at all a "weekend" home. "50 something" empty nesters expecting to live there for dare I say the rest of their lives.

Unknown

buffer

why couldn't you pipe & control the buffer like a large low-loss header where the supply sensor would be in a well in the tank? if you did this with a vitodens (which i believe modulates down to 18000 btu or so) this should work very effectively.

Mike T., Swampeast MO

With the constant circulation and TRVs, such a buffer would effectively disappear once the system was fully heated and maintaining space temp. Were such buffer also under reset control anywhere near "normal" for emitters of this type/size I believe it would prove to be nothing more than a needless drag on the system should the occupants want/need to increase space temperature.

Tom Hopkins

I wouldn't rule out a Prestige

Given that my design temp is 4°F and my gross consumption at it's highest was 40K - if I looked at my overall heating season since Mid-December to a 59° WWSSD, I had 67 days where it was greater than or equal to 30 HDDs (equiv. to 15-20K and up) and 75 days with very low loads that would be similar to heating that proposed house. There were no issues for the Prestige except at the lowest of loads some slightly varying indoor temps from having to deal with thermal gains that exceed the 5-6K it gives each 10 minute firing cycle - the variations could have been handled through TRVs - I envy your TRV'd setup.

Given that it had to run this over way half the season as it is, I see no issue why it wouldn't be a reliable and economical solution for the entire winter while being able to make a lot of hot water.

singh

A possible answer

http://www.heatinghelp.com/greenpdfs/52.pdf

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Mike T., Swampeast MO

This combination of extremely low load in a harsh environment where even an "efficient" envelope has more than twice the loss has forced me to re-think some things.

I've read about "perfect" commercial shells with HIGHLY controlled ventilation in far more moderate climates that can utilize large radiant panels (floors/walls/ceilings) at a constant year-round temp of about 75F. I believe this shell would achieve could achieve such in a 10,000 or so heating degree day climate!

Were it say 10 times the size (25,000 sq.ft) I would be designing for the highest possibile efficiency of the heat source with sophisticated control of such. At 2,500 sq.ft. I simply cannot find such to be in any way justified.

Far, far, far different than the usual systems I work with--gravity conversions in century-old homes...

Mike T., Swampeast MO

What's your calculated Manual-J (or similar) heat loss at such (4F, 40K output) conditions?

I sincerely expect the true load on this system to be no more than 12-14 mbh in their most brutal weather with less than 10 mbh load 95+% of the time.

It's almost like putting a VW "bug" engine into a zero wind resistance car the size of a Cadillac limousine and cruising the interstate at 100 mpg! Who cares if the engine is primitive when the system as a whole operates with exceptional efficiency?

hot_rod

The coil in the current Phoenix

is really more for a solar input, as it is at the bottom of the tank, below the burner.

HTP is working on adding and additional coil at the top for a radiant take off. That would be the better HX coil location as the tank stratifies.

It's the HTP Voyager tank that needs the small mix pump on the tank to get the performance out of the lower mounted coil. Two pumped flows helps the HX efficiency in the tank perform. The Voyagers extra HX really doesn't have much output at all when that mix circ fails. I have first hand experience with that concept.

With the Phoenix" solar" version you really don't want to "blend" the tank so the solar coil stays in the coldest possible part of the tank to leverage the solar panel efficiency. Make sense?

hot rod

Mike T., Swampeast MO

Very interesting...

I have the highest respect for "the Bean" and will only say that this system will do essentially the same thing with one "plain-Jane" device instead of three.

Nick S

Ahh, I see. That's too bad, the Bradford White is ok, but it would be nice to have a stainless tank for those not so good water areas and sealed combustion.

Mike, what are you doing for ventilation? ERV? HRV? A house this tight needs some fresh air! Right? Did you account for ventilation in your heat loss calcs?

hot_rod

The Bradford White Combi2 TTW

is a sidewall (through the wall) power vented appliance. I'd guess the "stack effect" losses would be similar to a mod con with a side vent application.

I'd agree the based on 19,000 design load in Caribou, Maine 70F at -13, 9770 degree day climate the BW Combi 2 would be a fine choice.

Either system would have a tank at 140F for DHW. The simplicity of the BW CombiCor 2 would attract me, and possibly the homeowner. It is very user friendly and repair-able by most any plumber.

One failed computer module, inducer fan, etc, etc would make the fuel saving between the 90%, $5000.00 mod con/ indirect system and the $2000.000 Combi, even at a 10% efficiency difference all but go away.

I can't get into the ASHRAE site right now, I be interestd in seeing their Table 1 "Hours of Temperature Occurance" for that location. I'd doubt design conditions of -13 are a winter's long episode?

This home could very well be heated with just the internal gains from appliances, lighting, occupants, etc for quite a bit of the winter if the load numbers are accurate, possibly even fudged to the high side by 15% or more by nature of the load calc program.

I think the Canadians did some extended testing with super insulated buildings like this a few years back, in regards to actual heating system loads. I'd bet Mr. bean could put his hands on that study?

hot rod

Tom Hopkins

Low Load - Small Input

Manual J was mid-50s.

Loads of 12-14 MBH or less showed the highest BTU/HDD - with a conventional boiler, the opposite is usually true.

I totally agree on the marginal nature of the fuel savings with a super insulated house (and I'd seriously go electric if my fuel bill for an electric boiler was under $1K), but still, I see no reason not to maximize FE in this application by minimizing stack temps and the related inefficiencies of bringing conventional boilers up to temp.

A mod con provides a small well controlled intermittent heat source that can also heat a lot of domestic hot water quickly. Very light loads are when mod cons have their best efficiency and where conventional boilers are at their worst.

Larry Weingarten

There was a question...

... earlier about whether or not this house has a heat recovery ventilator (HRV). Also, was that factored into the heat loss calcs? http://www.passivehouse.com/ is a site to have a look at. It sounds like your client is building the third passivehouse in the US! Any chance of using solar with a well insulated tank and low temperature emitters?

Yours, Larry

mars_4

T 50 Heat Transfer Products boiler

Mike it seems to me that the wall hung T50 from heat transfer products might fit in this situation. you could very easly mate it up with a 40 gallon super store inderect for dhw production and still have the cappilibility of running it on out door reset. I belive you can run this boiler down to a very low operating temp and gain the most energy efficieny out of it, with the vision controll that they offer. just my two cents.

Mars

Unknown

the numbers might bear out the heat source selection, that's fine. But I am taking umbrage with two of your statements here.

1. If your supply temp requirements are what you say they are, then reset is called for. If not at 140 to 160, then where would you ever use ODR? ODR gets less useful as the maximum supply temperature falls, not vice versa. Perhaps you might say that it's not as necessary for comfort due to the low mass emitters and supertight envelope, but I would expect the supply temperature requirements to also be commensurately lower in that case. I can't see periodically pulsing high temp as a great choice, and you need SOME kind of heat injection/modulation if you're doing constant circulation. So why not make it reset? It's cheap and it's easy.

If you say the envelope makes ODR unnecessary, then wouldn't it also make sluggish response nearly impossible? Opening a door may increase the percentage of heat loss, sure, but it's still made up by the refridgerator More seriously, the opening of a door for a reasonable period of time is NOT going to lower the MRT of all this wall, floor, ceiling, etc, ever. I think your response time concern is a non-issue unless you are completely unable to get the clients to understand the constant heat methodology, which especially in super insulated homes is the strategy of champions! But even if they attempt setback (with TRVs.. somehow), in this envelope they won't lose enough heat for it to really matter.

Unknown

Also, the buffer tank idea is not invisible (I was thinking about this last night).

If your heat source were actually in modulating mode, then it's invisible... which is fine, because you're already modulating.

If your heat source is NOT in modulating mode, it fires on a differential. The differential spread is what utilizes the buffer capacity of a buffer tank. And when it is not in modulating mode, that's when you want to start thinking about buffer capacity anyway.

I would do as zac suggested IF the numbers defend the choice of a mod/con, and use a boiler buddy or other buffer tank as a LLH.

Mike T., Swampeast MO

Yes, there is definitely an HRV (three outlets) and it is factored in.

Mine is the third heat loss calculation. One (specified Manual-J based by a heating contractor) came in at 18mbh. Another (unspecified method by a supply house) came in at 28 mbh.

He has not mentioned solar at all. My only mention is that it is not well-suited for passive solar gain. Porches completely cover the N, E & S sides and the long sides of the rectangular footprint face E & W. Very little southern glass--none on the ground floor save the in the good-sized enclosed entry (unheated) built external to the shell.

The exterior walls are complete but the attic is not yet insulated. They're already having nights in the low 40s. His wife told me that it's perfectly comfortable and windows are routinely opened. Windy, exposed location. Wife reports "not even a hint of a draft" and almost deathly quiet inside.

Were construction not so far along and time so tight, I may well have suggested that your modern gravity radiant walls be "borrowed"--even if it didn't include the solar drive.

As is, I'm trying for the next best thing. Well-heated "ribbons" hanging on the walls...

Their heating season runs from September through May. Based on their average temps, I suspect it will be passive from late April through early October.

Mike T., Swampeast MO

Just heard from "the Bean" and given three choices of heat source--Bradford-White; Phoenix; mod-con--he chose the Bradford-White.

Larry Weingarten

It'll be fun...

... to measure "imported energy" in BTU/sq foot(of living space)/year, once the house is complete and has had time to gather some data. Normal new construction uses 100,000 to 130,000, passive house homes use no more than 38,000 and my house so far uses 12,000. Yes, I'm pleased ;~) Imported energy measures all energy input, not just heating/cooling... so it's both structural requirements and lifestyle choices. In my book, solar is not imported energy, but if one covers the roof with photovoltaics, the house price will jump, so there must be a balance between efficiency and cost. I'm getting by on 630 watts of PV.

Yours, Larry

PS_2

BIN hrs

I'm not going to enter all the data points, but the annual BIN hours for Loring AFB (15 miles away)shape up this way:

3,591 hrs @ 32 degF or less
~ 600 hrs @ 0 degF or less
< 30 hrs @ -20 degF

Mike T., Swampeast MO

I'm in this project at the very end. Specifying the space/DHW heating system based on info provided to me.

Architecturally designed with significant homeowner input.

Homeowner found me at "The Wall" and as best I can tell was at near wits end with nobody near him really comprehending his requested method of heat (TRVs with true constant circulation) or being able to identify a "proper" heat source--or even emitters--given the extremely low losses. At least one pro told homeowner that it was "impossible" to have a house that size in that area with that low of a heat loss. I haven't asked, but homeowner appears to be acting as his own GC with the project ongoing for more than a year. He reports "obsessive" attention to detail regarding infiltration.

When I asked if the doubled 2x6 exterior walls were installed without thermal bridges, his reply was "pretty much". At that point I knew he was rather like me--utterly "perfect" plans in his head, but finding that reality required concessions of "close enough".

DEFINITELY an HRV (no need for a ERV in a cooling climate with no A/C planned or needed).

Mike T., Swampeast MO

Rob,

I'm not trying to duck your questions, but I'm so far into theory regarding actual heat requirement vs. calculated heat loss as modified by human comfort desires that I can only give Billy Joel's best words:

"You may be right. I may be crazy. But it just may be a lunatic you're lookin' for. Turn out the lights--don't try to save me. You may be wrong, for all I know but you may be right."

Something tells me the Catholic church had such things in mind when they gave him an honorary doctorate degree in "good letters" (or something like that) even after "...don't make me wait.. Catholic girls start much too late..."

It's often fun to be an inegmatic dichotomy--JUST LIKE ENERGY TRANSFER VIA RADIATION.

Mike T., Swampeast MO

If you'll grant me the contention that huge gravity piping is virtually the same as a series-connected buffer then I can assure and verify that such buffer "disappears" in a TRVd constant circulation system once the heat requirement is less than about 50% of minimum modulation. And that's when my Vitodens operates with 40+F differential temperature. (Remember that the Vitodens 200 does NOT have a fixed differential--the control does its best to adapt the differential to best suit the system to which it's connected.)

Mike T., Swampeast MO

Homeowner's previous house in northern PA USED a geothermal heat pump. Wife watched the indicators and found "lots" of pure electric resistance backup.

Cannot comment about the system--ONLY the homeowner observation...