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Heating Super-insulated houses
jp_2
Member Posts: 1,935
I agree with constant circ, but here you might be able to use setback to an advantage. higher ramp up temps in morning could give the feel of "warm floors", maybe a short ramp up in the evening too. then ramp down to normal floor temps to prevent large over swing.
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Comments
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Heating super insulated houses
I'm an architect working on a project that is basically a semi-detached condo building in Southern VT, near the Mass border. It is in the late planning stage. Each unit is roughly square and is approximately 1500sf. The walls are SIP Panels (R-40) and the roof is (R-60). The foundation is insulated slab on grade. The Owners of the complex hired a heating expert that recommended against radiant floor heating due to slow responce. It was suggested that rinnai units be used as point source heating. Several owners want to heat with decorative vented gas stoves. One wants electric baseboard due to allergies. To complicate matters, several owners have asked to convert their utility rooms into living space. I'm investigating flat panel radiators and TRV's as well as propane wall hung boilers. The proposed solution for domestic hot water is one gas instantaneous heater per unit, located in the bathroom. I worked on a hotel project several years ago using electric instantaneous heaters which did not work very well and were replaced. Each unit will have a HRV system. Any suggestions?0 -
Just one....
Punt! Chris0 -
Radiant- Hands Down (Feet Down Too)
Given a choice, radiant with excellent controls would win in a heartbeat.
The notion that there is slow response has to be qualified. If a high-mass masonry structure with so-so insulation and deep setbacks, yes. But with R-40 walls and R-60 roofs, a good baseline temperature and comfort can be maintained with very little effort and at very low temperatures. Imagine heating with 85 degree or lower water? Your construction might support that.
My only concern would be to find a small enough heating appliance to take on that small load. A small ModCon (modulating condensing boiler) coupled to domestic HW would be ideal but they seem to start at the 50-80 MBH range.
Using a domestic water heater "could" work but only if your local code permits AND the heating is on a separate circuit totally isolated by a plate heat exchanger from the domestic water. This latter part is good practice and transcends code regardless.
Electric resistance heat in any of it's forms for total building heat would be expensive in the long run, even with a small-ish heat loss. A water to water ground-source heat pump could be considered but first cost for wells and loops might eat into your bottom line in a hurry.
Nothing wrong with vented gas stoves, Rinnai and Monitor space heaters and such. Panel radiators are a good second choice to radiant, IMHO. You do have choices. But start from radiant and find reasons why you cannot.
My $0.02,
Brad"If you do not know the answer, say, "I do not know the answer", and you will be correct!"
-Ernie White, my Dad0 -
Use caution with super insulated buildings and radiant slabs
first off do a heat load for the home. Room by room ideally.
What you may find are some low loads oer square foot.
Let's assume a 16 btu/ square foot load for this example.
If you target a room temperature of 70F on a design day, you would need a mere 78f supply temperatures. As you get @ 2 btu/ square foot output for every degree difference.
Now that is at design outdoor temperatures, let's assume 0F. Run the numbers and look what hapopens at 32F outdoor, or if the loads fall below 16 BTU/ sq. ft. I've seen some SIP and ICF homes fall into the 12 BTU/ ft. range in my area.
You are entering a zone where the occupants may not feel warm floors, as 83- 85 is closer to skin temperature. Mid 70"s on thr floor surface will feel cool not warm to bare feet, even though it may be enough to warm the space.
So prepare the owners for lukewarm floors, not the toasty warm often "assumed" with radiant.
I've been trying to "design" around these low energy homes, I've found often times the lighting, refrigerator, and Viking range alone will warm the space without any floor output!
Perhaps just radiant floor panels under the sitting and traffic areas? Maybe leave a 2 foot perimiter areond outside walls un-heated to change the heat flux to the "walked on" areas.
Or TRV-ed panel rads with radiant floor in the baths and maybe kitchen.
Radiant ceiling or walls perhaps?
Just be careful what you promise with radiant floor heat in low, low load spaces
hot rod
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Hi effecient homes
> first off do a heat load for the home. Room by
> room ideally.
>
> What you may find are some low
> loads oer square foot.
>
> Let's assume a 16
> btu/ square foot load for this example.
>
> If you
> target a room temperature of 70F on a design day,
> you would need a mere 78f supply temperatures.
> As you get @ 2 btu/ square foot output for every
> degree difference.
>
> Now that is at design
> outdoor temperatures, let's assume 0F. Run the
> numbers and look what hapopens at 32F outdoor, or
> if the loads fall below 16 BTU/ sq. ft. I've
> seen some SIP and ICF homes fall into the 12 BTU/
> ft. range in my area.
>
> You are entering a zone
> where the occupants may not feel warm floors, as
> 83- 85 is closer to skin temperature. Mid 70"s on
> thr floor surface will feel cool not warm to bare
> feet, even though it may be enough to warm the
> space.
>
> So prepare the owners for lukewarm
> floors, not the toasty warm often "assumed" with
> radiant.
>
> I've been trying to "design" around
> these low energy homes, I've found often times
> the lighting, refrigerator, and Viking range
> alone will warm the space without any floor
> output!
>
> Perhaps just radiant floor panels
> under the sitting and traffic areas? Maybe leave
> a 2 foot perimiter areond outside walls un-heated
> to change the heat flux to the "walked on"
> areas.
>
> Or TRV-ed panel rads with radiant floor
> in the baths and maybe kitchen. Radiant ceiling
> or walls perhaps?
>
> Just be careful what you
> promise with radiant floor heat in low, low load
> spaces
>
> hot rod
>
> _A
> HREF="http://www.heatinghelp.com/getListed.cfm?id=
> 144&Step=30"_To Learn More About This
> Professional, Click Here to Visit Their Ad in
> "Find A Professional"_/A_
0 -
I second Hot rods statements
> first off do a heat load for the home. Room by
> room ideally.
>
> What you may find are some low
> loads oer square foot.
>
> Let's assume a 16
> btu/ square foot load for this example.
>
> If you
> target a room temperature of 70F on a design day,
> you would need a mere 78f supply temperatures.
> As you get @ 2 btu/ square foot output for every
> degree difference.
>
> Now that is at design
> outdoor temperatures, let's assume 0F. Run the
> numbers and look what hapopens at 32F outdoor, or
> if the loads fall below 16 BTU/ sq. ft. I've
> seen some SIP and ICF homes fall into the 12 BTU/
> ft. range in my area.
>
> You are entering a zone
> where the occupants may not feel warm floors, as
> 83- 85 is closer to skin temperature. Mid 70"s on
> thr floor surface will feel cool not warm to bare
> feet, even though it may be enough to warm the
> space.
>
> So prepare the owners for lukewarm
> floors, not the toasty warm often "assumed" with
> radiant.
>
> I've been trying to "design" around
> these low energy homes, I've found often times
> the lighting, refrigerator, and Viking range
> alone will warm the space without any floor
> output!
>
> Perhaps just radiant floor panels
> under the sitting and traffic areas? Maybe leave
> a 2 foot perimiter areond outside walls un-heated
> to change the heat flux to the "walked on"
> areas.
>
> Or TRV-ed panel rads with radiant floor
> in the baths and maybe kitchen. Radiant ceiling
> or walls perhaps?
>
> Just be careful what you
> promise with radiant floor heat in low, low load
> spaces
>
> hot rod
>
> _A
> HREF="http://www.heatinghelp.com/getListed.cfm?id=
> 144&Step=30"_To Learn More About This
> Professional, Click Here to Visit Their Ad in
> "Find A Professional"_/A_
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Combi
First of all, if there is any way to keep the utility rooms, please do so. Just because they don't want a utility room, doesn't mean they don't need a utility room.
There are a few "Combi" wall-hung boilers that provide both heating and domestic hot water. These boilers are made for situations like this where space is at a premium. A Vitodens 200 6-24C would fit well.
Constant circulation with outdoor reset helps reduce the effect of the mass of the concrete radiant floor. Panel radiators with TRV's would be a good match to the radiant slab for upper levels.0 -
I second Hot rods statements
I built a 1-1/2 storey 1800 ft home three years ago, 1140 sq ft on the main floor level with ICF walls, stick frame second floor with icynene insulation. My design temp here in Manitoba
Canada is Minus 27f design heat load is 16 btu per ft but in
use has turned out to be closer to 10btu's per ft, the floor temp is very often cool to the touch even at very comfortable
room temps of 72f. I have had times where the floor has not been on for 2-3 days even at outdoor temps of -15f, because of the heat gain from lights fridge people etc.
I wish I had put in the floor sensor before pouring the floor but in the rush it got forgotten minimum floor temp could have helped maintain a more comfortable floor.
The other problem is cooling,because of the way the building
retains heat, cooling can be need at very low outdoor temps
ie: low fourty's and above so would recomend heat pump over A/C0 -
Slabs are one thing
Your points regarding "expectations" are right-on, Hot Rod. And if concrete slabs are part of the picture, there is that flywheel effect.
It goes as standard practice that you start from calculations (you know this obviously, not meant as a challenge) so the floor layout becomes critical as does the temperature of the water supplied and the ability to control it.
From what I see of this project, I would think a low-mass underlayment system such as Climate Panel, RAUPANEL or others with faster response would be the choice, using very low water temperatures and micro-flows.
Use of PID or PWM limiting control would be key. High solar areas and a good refrigerator pretty much take out the heat loss of nearly any space.
The SIP construction pretty much wipes out the MRT (mean radiant temperature) effect so a lower setpoint should yield equivalent comfort compared to a conventional structure.
That said, low density radiant would still be my choice.0 -
this is superinsulated. The floors will never be warm anyway.
Provided the floors themselves are insulated, I would use whatever works, it won't make much of a difference, and train the clients not to set back at night.
If you want "uber deluxe", Slab radiant with indoor feedback systems will work fine, much more cheaply than any panel product, they just can't CHANGE indoor temperature fast. I would only do this to make sure the floor isn't cold and to make sure they are not setting back at night which would allow the floor to get cold and compromise comfort long term, radiant or not. The key here is going to be consistent heating of any kind.. if consistent, the floor will get to room temp eventually. I myself lived in a superinsulated house with a rinnai, and the room with the rinnai in it (not the rest of the the otherwise unheated house, but the big open 1st floor) was very comfortable once I got my then-fiance to stop turning down the heat at night.
A cheaper radiant ceiling with simpler controls, or panel radiators if visible heat are ok, are good hydronic options as well.
There is absolutely no need to go to expensive panel products in this case though. That's a whole lot of cost for no real benefit here.0 -
SIPS home
Last year,we completed a 4000SF home with SIPS walls R40 attic/roof insulation and radiant heat throughout with overpours and a slab at grade. A Vitodens 6/24 with an 80g VitoCell indirect tank do the job. The actual radiant heat loss was 24K Btu's. The heating curve is set at .5 The heating bill last winter was $500.00, which includes the potable hot water. Most of the time, the Vitodens modulates at low idle, ramping up for DHW recovery only.
The owner (a Boeing engineer) says the home stays within 1 degree of setpoint in any room.
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The windows
Funny nobody asked about the windows. In a super-insulated building, the windows had better match the rest of the envelope performance, otherwise you're using screen doors on a submarine. I hope that the windows have a centre of glass U value of at least 0.24 or better with a really good thermally broken frame in order to minimize their impact on the thermal loads, and mean radiant comfort of the space. Also- are the solar gains policed up? The biggest design problem with these types of homes is the large differential transient thermal loads created by poor fenestration and solar control.
That being said- I'm with the others- radiant is the best solution for low energy, comfort, and allergy issues. I'm with the post that suggested limiting the radiant floor to traffic zones to enable higher floor surface temps at the low loads. There are a number of different radiant floor systems as well: high-mass systems with slabs or concrete topping, with their slow response, or lighter mass systems which have a "quicker" response time, with manufactured sub-floor systems like Warmboard, Raupanel, Quik-Trak, to name a few.
The trick is to design the right kind of heat emitter to match the nature of the transient loads in the room and building. With good solar control and good window thermal performance, the transient heat losses and gains will be fairly small and not as "quick-acting", so a slow response radiant system is a good match. If you have crappy windows, and lots of them, then the windows and solar transients will create a need for a quicker response heater/emitter to respond to those fast-acting transient thermal loads from the windows. The air side ventilator can also be used as a quick-reaction force to heat and cool those fast-acting thermal loads as well, if you have an astute controls guy working with you to set up the staging of the thermostatic controls.
As a last note, and as an allergy sufferer, electric baseboards are the LAST type of heater that should be used for allergy people- the dust and crap that collects on the fins and then gets toasted every time the electric element turns on is horrible. Electric baseboards also provide most of their heating by convection, which can entrain floor level dust into the convective air coming off the baseboard, and can create a lot of floating dust compared to floor radiant systems.
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Hmm...
Given the location and the insulation schedule of the structure, I doubt that the load is going to be very high, as long as the architecture is done right.
By that, I mean sufficient overhangs over south-facing windows to keep the summer sun out and the winter sun in, triple-pane windows and well-insulated doors, etc. Even with overhangs you might have heating loads that are so low that even the winter sun on a design day toasts the place.
If the insulation is consistently good, I would be surprised if the heat loss on a design day was not below 10BTU per square foot. To put things in perspective, our 130-year-old girl has R25 walls and a number of R2 windows and still manages 12BTU per square foot on a design day. To go lower would have meant abandoning historic windows...
It's conceivable that point-of-use heating appliances like gas fireplaces will do the job, though I'd like to limit building envelope penetrations as much as possible.
From an aesthestic point of view, the baseboards from Hydronic Alternatives would allow you to install a effective heating system along the outer perimeter without resorting to RFH. These baseboards may also be more effective than RFH at countering "the cold" of radiant heat transfer via the windows.
If you end up using RFH, I'd consider using some BTU meters and a single boiler plant instead of individual units. That minimizes space requirements and should be cheaper than installing individual heating units. You could install two small boilers for redundancy and super-efficiency. With stainless IDWH tanks, you'll never have to worry about running out of hot water and it keeps the utilities out of the units themselves."Let me control you"
Lost in SOHO NYC and Balmy Whites Valley PA0 -
another kal on the wall - o-boy...
the Brooklyn kal says, use electric radiant where people are going to be bare feet such as baths - and radiant panels for the rest - if you do high mass radiant in a super insulated house you better have slab sensors and drive the mean temps ramp ups and downs, 12 hours in advance with input from the weather channel good luck with that
- the only complaint I ever got on a high mass radiant was too hot in a super insulated house - it took three days to cool it down to desired temps so subtract at least 20% from the heat loss calc results, the other option is low mass radiant with aluminized subfloor panels that the pex tubing presses into expensive but quick response but, if I build a house again its will be cast iron rads under windows simple radiant heat the dead men were onto something!!! 0 -
Right on with the floor temps..
The house I just finished has the spray in insulation and it was designed for floor WARMING under the traffic areas and bathrooms only. I find that if the floors go much over 75* on the milder days it gets too warm, so they ARE cool to the touch. I explain it beforehand by saying, "The floors won't feel warm , they just won't feel cold. If the floors feel warm, it get's too hot in the room." Sun can be a problem on the cool days when the A/C is off and the sun is beating through the family room's two story wall of glass that happens to face west. They aren't living there yet but we'll get more info once they move in and time goes by. The floors are supplemented by hot water fan coils and so far we've been running the whole house on 110*F water with an 8* differential. (102*-110*) So an average of 106*.0 -
I am the Rinnai rep for your area
I will be happy to meet to examine the plans/site etc to advise as to the application of the on-demand water heater and the Rinnai DV wall furnaces. May I help you? My cell is 617 834-87510 -
superinsulation
I live in a superinsulated home with infloor heat (2" of concrete on wood subfloor on TJI's. 8-12 btu/hr/ft2 is definitely the range I'm in as well, considering internal heat gain.
Temperature swing is never a problem, even with a lot of solar gain. The control system is dead simple: bang-bang thermostats, 5 zones.
However, considering how little the boiler comes on, and how seldom the floors feel warm, next time it's forced air for me because I like to be able to filter and humidify the air. You still need A/C of some sort anyway.Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments0 -
That's why...
I like to do radiant warming on key floors and the rest hydro air. Now I can humidify and filter during the winter. I'm putting in the air handlers for A/C anyways, why not use them for part of the heat too? I also knock some $ off my quote because I'm not putting tube in all the floors. Keeps me competitive.0 -
SEE Chris...
I wasn't lying at 6 this A.M. PUNT!
You've got almost as many answers as responses...The BIG factor in the equation is (Dunt DA DA DA !)) THE OCCUPANT!
If these units are "pre-sold" and the OCCUPANTS have any say....MAKE THEM SIGN A DISCLAIMER!!!!!
Give them what they WANT...but make yourself "unavailable" if the suspected "PROBLEMS" arise.
I have to agree with Brad and Hot Rod on most points...but there have been some other well respected points brought up also....
Make the OWNER responsible for their decision and take all necessary actions to give them what they want, without being held accountable for their discomfort because of all the points spoken of.
You've got the information..let THEM make the decisions!(Bow gracefully!) The other Chris.0 -
not radiant
I think that the reasoning for staying AWAY from radiant is that units like this are frequently weekend stay units. The heat is set low all week, then cranked up on Thurs. night or Friday for the weekend.
Along with htat usually comes an extremely high DHW demand, as everyone wants a shower after the day's activities (skiing, hiking, etc.).
I have sevearal communities like this in northern Maine, although not as hyper insulated, and they were a bear to size for equipt.
I would think that a modulating combi unit with either conventional baseboard or panel rads would be the best fit. Comfortable, efficient heat and DHW, and fairly fast response.
Guy Woollard
N.E. Regional Sales Mgr
Triangle Tube Corp.0 -
A phone switch can solve the rapid response issue as well, just as one other option.0 -
Find a new contractor
Radiant and super-insulated homes are meant for each other.
I built such a home and installed such a system. Where? Same state! I invite you to take a look at my fuel bills, the heating system in use and the nature of both SIP and ICF construction.
One of my fellow Champlain Valley ASHRAE members mentioned this project to me recently.
If I can help, call or e-mail me.
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absolutely
You are right about that, however those in charge often look at that as excessive run time as well, despite the overall savings of the radiant. Having the heat rising for the day before seems wasteful to them. Besides, where's the spontanaiety! ;-)
Guy Woollard
N.E. Regional Sales Mgr
Triangle Tube Corp.0 -
they are partially heating an unoccupied house for occasional weekend use, and one extra day of heating up is wasteful??
Someone should have a more frank conversation with them about conservation, if so!0 -
> I agree with constant circ, but here you might be
> able to use setback to an advantage. higher ramp
> up temps in morning could give the feel of "warm
> floors", maybe a short ramp up in the evening
> too. then ramp down to normal floor temps to
> prevent large over swing.
These units are year used year-round. The owners are mainly older. Thanks for the suggestions. I meet with six of the owners tommorrow. The heating solution may be wall hung boilers in the bathroom in most units. Rinnai in others.
Chris0
This discussion has been closed.
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