Posted By DarkNova on 24 Aug 2014 09:23 PM
Thanks for the comments and calculations.

And thanks to Borst Engineering for that steady-state room calculator. It works well.

It showed that at a -13F temperature, in a corner bedroom with good windows and good insulation, with 69F in the rest of the house, that room could get down to a steady-state of 57.5F. Unfortunately that is pretty low and makes me second-guess pursuing mini splits for our climate.

I will still look at them more, as coupled with fans it could still possibly work, but as jonr showed it takes quite a bit of air movement to even out the temperatures.

The reason I am interested in pursuing an electrical heating option is that this is a rural property, so it is either electricity or propane. Propane isn't cheap, and our electrical rates are really cheap (~ $0.06/kWh) so it seems like the way to go.

GSHP/geothermal has a high up-front cost that would probably not be paid back in decades on a well insulated house.

I would be interested in an air source heat pump that could be fed into a central ducting system, but I have not seen one so far that can perform down to cold temperatures like the Hyper Heat Mini Splits.

If anyone has any other suggestions to look at, I'd be grateful.

Unless it's below -13F for many-many hours during the heating season, using cheap baseboards or electric cove heaters to manage the peak loads in a bedroom backstopping the bedroom temp at 65F or something (keeping the mini-split at 72F or whatever)  is going to be pretty cheap both to implement & operate, and the  mini-split is still carrying the lion's share of the load.

At -13F a Mitsubishi mini-split is delivering a COP of 1.8-2, the use of resistance heating as the backstop might reduce the average COP to something like 1.5 during peak load periods, but the rest of the time the mini-split is carrying ALL of the load, at a COP well north of 2.  Over the course of the heating season you'd probably still average a COP of 2.5 or better using the -FHxxNA hyper heating units with baseboards as the "Hail Mary" backstop.

I don't know what the house design is, but looking at some rough numbers, a concrete slab (or wall) in the room should prevent > 10F temp drop over an 8 hour closed door period. Even gypsum wallboard will help a little.

Hopefully, at some point many of the air to water HPs that are available in Europe will make it to NA.

Where electricity isn't available, a propane generator with heat recovery (CHP) driving a HP (air or geo) might make sense. Preferably with thermal storage.

Most of those European air-to-water heat pumps won't cut it in US climate zone 7. IIRC When tested in Sweden a few years ago the Daikin Altherma led the pack on efficiency in a Scandinavian climate, which has mid-winter average temps more like zone 6 than zone 7.

The Fujitsu Waterstage is rated to -13F. And with to water heat pumps making storage (in tanks or slabs) easy, low temp performance is a little less critical (you can catch up during the day).

Jonr, your thermal mass logic again needs some refinement. Having interior thermal mass in a closed, unheated room will NOT “prevent” the room from reaching its steady state colder temp. This interior thermal mass will only increase the time that it will take the room to reach its steady state colder temp. However, this interior thermal mass will also increase the time that it will take the room to return to its desired warm temp once the room is again heated. So while this interior thermal mass will tend to stabilize the indoor room temp (i.e., reduce the rate at which the temp will change), there is zero economic heating benefit for using interior thermal mass if you are paying for the energy used to heat the interior thermal mass.

DarkNova: There have been many homes build in the northeastern US in the past few years using minisplit heat pumps. I've not heard of anyone mentioning a temperature differential more than a few degrees between rooms. There are many articles about these units and how they functioned during last winter on GreenBuildingAdvisor.com. I built one last year, a vacation house, and told the owner to keep the bedroom doors open. I went back a few times for various reasons - the doors were always closed and I noticed no difference in temperature. The key is to build a very tight house; ideally at or under 1.0 ACH50.

sailawayrb: You should notice that I wrote "over an 8 hour closed door period" and didn't say anything about economic benefit (the OP is concerned about bedroom comfort). My statements are correct and you are making up straw man arguments.

Jonr, your statement is unsubstantiated, which is all too often the case. A 100 SF concrete slab of 4 inch thickness initially at 70F and located in a room having a 57.5F steady state temp will cool to 64.1F in 6 hours and to 61.0F in 12 hours. More importantly, it will take a considerable amount of time and energy to reheat it back to 70F. This would NOT lead to a comfortable living space.

Posted By ICFHybrid on 24 Aug 2014 10:45 PM

They probably only need 2kw. It doesn't make sense.

I doubt very much that the contractor is putting arrays on that are larger than what the home needs A 2 kW array would generate roughly 8-12 kWh per day. Since the average home uses 1200 kWh per month, 240-360 kWh would represent a substantial shortfall. In addition, the homes are using electricity for the heat pumps, so it is likely they use at least the average.

You can doubt all you want, but here is another article about Carter Scott.


http://solartoday.org/2013/03/energy-positive-homes-in-devens-mass/

DarkNova: I think my family could tolerate around 60F in bedrooms

jonr: ... should prevent > 10F temp drop over an 8 hour closed door period.

No Jonr, I would never support a statement that doesn’t first provide some basis of fact to support it. So I ran the numbers using the thermal mass software on our website to actually determine the temp decay of this example slab in accordance with Newton’s law of cooling. Only DarkNova can say if having to wait a prolonged time to heat the room back to 70F from 62.9F (i.e., approximate temp after door has been closed for 8 hours) would be acceptable to his family. Furthermore, I don’t know if DarkNova has anything like this high level of thermal mass planned for this room. Using less mass would reduce the time to reach the steady state temp and the need to have to reheat from a temp even lower than 62.9F.

Bob I, while I didn’t see what DarkNova actually ran to obtain his steady state room temp of 57.5F, the software didn’t include any infiltration/ventilation modeling at the time. So any infiltration from the outdoors into the closed, unheated room would have only lowered this steady state temp further. However, I suspect that it is more likely that there will be significant infiltration from the heated living space into the closed, unheated room which could significantly raise this steady state temp and perhaps explain your experience of not seeing a very great temp differential. Interior doors often have significant gaps and interior walls are often not well sealed.  Of course, there would need to be some pressure differential to create this interior infiltration.  Anyhow, I updated the software on our website to allow entering infiltration/ventilation parameters.

Posted By eugenep on 24 Aug 2014 04:11 PM

Posted By ICFHybrid on 23 Aug 2014 10:45 AM

I think that $330,000 for that house is pretty expensive

The house you are referring to didn't cost $330,000. It sold for $195,200, which included the land and builder profit. What it says in the article is that Mr. Scott's company plans to build a number of other very efficient homes, some with 4 bedrooms that will sell for up to $330,000.

You could easily build a much larger house for less using a normal hvac system

That's the same greedy thinking that has caused the very problem people are trying to solve. A major tenet of Green Building is to build homes that don't waste energy just because it is unaccountably cheap. BTW, Carter Scott notes that a "normal" HVAC system for this house would have cost his company about $14,000 and they did this one for $7,500, or about half. Building more efficient envelopes pays off in terms of spending less on the heating plant to begin with.

I don't think most people are looking at a 2-story that small.

That's exactly the kind of home a number of new families are looking at, as well as a number of older couples where the kids have moved out and the parents are looking to downsize. The difference might be in the level of finish afforded. A nice feature of the energy-efficient homes for both couples starting out and for retiring couples is that the energy costs are more predictable and controllable, making it easier on budgets.

In one town, the houses start at $330,000.   Of course, you picked the town which says they go up to $330,000.  Whatever.  They don't specify the size.  It isn't greed.  It is the the concept of diminishing returns.  He is putting 17kw on some of these houses.  They probably only need 2kw.  It doesn't make sense.

I found a few more articles about his homes, and they say they are saving $500/month in utilities.  My sister who lives in Massachusetts in the crappiest house in the world with hardly any insulation, wet basement, minimum attic insulation, 2 story house with a basement, doesn't use $500/month in utilities, so it would be impossible to save that much/month.  Her house is 1450 sq ft and 45 years old.

So, I am doubtful of most of the numbers that people quote.  Maybe, he gave us his highest quote that he wouldn't use.  Who knows.

I don't think most older people want to buy a small 2 story house.  Maybe, in your part of the world, but most people say when they get older, they don't want to climb steps.

Carter Scott's typical Net Zero Energy houses have between 5-10KW of PV on them- the 17KW example is an outlier. (Trying to cover the pool heating energy too, mayhaps? ) 

I've never met anybody  in MA who could heat & light their house on the annual output of 2KW of PV array- that would barely cover the annual lighting & entertainment equipment loads at my house (even if I DIDN'T have the limiting shading factors), and wouldn't come close to covering the heating & cooling loads even with the best-in-class heat pumps.

Your sister apparently is not heating with #2 oil or propane in the crappiest 1450' house in Massachusetts. Plenty people in central MA living in 1200-1500' 1960s vintage houses with R19-R30 in the attic and at least R11 in the walls are spending more than $3000/year just on heating oil or propane, and another $1000/year on electricity. (I know several of those people personally.)

In the same area people are living in ~3000' 2x4 framed houses with no wall insulation (none!) and at best  R19 in the attic, heat the place with 70% efficiency steam boilers and pay maybe $400 on the coldest month for heating, and maybe $2000/year total, by virtue of being on the gas grid. (I know several of those people too.)

Those living off the gas grid have quite a bit more financial incentive to go with high-performance houses & heat pumps, given that propane and oil BTUs cost about 3x as much as natural gas at local grid pricing. The marginal cost of ductless heat pump BTUs is cheaper than 70% efficeincy gas, but more expensive than condensing gas, but still well under half the cost of heating with oil or propane (or resistance electricity, at 15-20 cents/kwh.)

But I don't know anybody in MA living in a barely insulated ~1450' house off the gas grid who is spending less than $500/month during the winter in heating fuel + electricity to stay warm in January. With a mini-split in a municipal owned utility town with low-cost electricity, or somebody who cuts & splits their own cordwood could probably duck under that bar...

Posted By Dana1 on 25 Aug 2014 05:38 PM

Posted By eugenep on 24 Aug 2014 04:11 PM

Posted By ICFHybrid on 23 Aug 2014 10:45 AM

I think that $330,000 for that house is pretty expensive

The house you are referring to didn't cost $330,000. It sold for $195,200, which included the land and builder profit. What it says in the article is that Mr. Scott's company plans to build a number of other very efficient homes, some with 4 bedrooms that will sell for up to $330,000.

You could easily build a much larger house for less using a normal hvac system

That's the same greedy thinking that has caused the very problem people are trying to solve. A major tenet of Green Building is to build homes that don't waste energy just because it is unaccountably cheap. BTW, Carter Scott notes that a "normal" HVAC system for this house would have cost his company about $14,000 and they did this one for $7,500, or about half. Building more efficient envelopes pays off in terms of spending less on the heating plant to begin with.

I don't think most people are looking at a 2-story that small.

That's exactly the kind of home a number of new families are looking at, as well as a number of older couples where the kids have moved out and the parents are looking to downsize. The difference might be in the level of finish afforded. A nice feature of the energy-efficient homes for both couples starting out and for retiring couples is that the energy costs are more predictable and controllable, making it easier on budgets.

In one town, the houses start at $330,000.   Of course, you picked the town which says they go up to $330,000.  Whatever.  They don't specify the size.  It isn't greed.  It is the the concept of diminishing returns.  He is putting 17kw on some of these houses.  They probably only need 2kw.  It doesn't make sense.

I found a few more articles about his homes, and they say they are saving $500/month in utilities.  My sister who lives in Massachusetts in the crappiest house in the world with hardly any insulation, wet basement, minimum attic insulation, 2 story house with a basement, doesn't use $500/month in utilities, so it would be impossible to save that much/month.  Her house is 1450 sq ft and 45 years old.

So, I am doubtful of most of the numbers that people quote.  Maybe, he gave us his highest quote that he wouldn't use.  Who knows.

I don't think most older people want to buy a small 2 story house.  Maybe, in your part of the world, but most people say when they get older, they don't want to climb steps.

Carter Scott's typical Net Zero Energy houses have between 5-10KW of PV on them- the 17KW example is an outlier. (Trying to cover the pool heating energy too, mayhaps? ) 

I've never met anybody  in MA who could heat & light their house on the annual output of 2KW of PV array- that would barely cover the annual lighting & entertainment equipment loads at my house (even if I DIDN'T have the limiting shading factors), and wouldn't come close to covering the heating & cooling loads even with the best-in-class heat pumps.

Your sister apparently is not heating with #2 oil or propane in the crappiest 1450' house in Massachusetts. Plenty people in central MA living in 1200-1500' 1960s vintage houses with R19-R30 in the attic and at least R11 in the walls are spending more than $3000/year just on heating oil or propane, and another $1000/year on electricity. (I know several of those people personally.)

In the same area people are living in ~3000' 2x4 framed houses with no wall insulation (none!) and at best  R19 in the attic, heat the place with 70% efficiency steam boilers and pay maybe $400 on the coldest month for heating, and maybe $2000/year total, by virtue of being on the gas grid. (I know several of those people too.)

Those living off the gas grid have quite a bit more financial incentive to go with high-performance houses & heat pumps, given that propane and oil BTUs cost about 3x as much as natural gas at local grid pricing. The marginal cost of ductless heat pump BTUs is cheaper than 70% efficeincy gas, but more expensive than condensing gas, but still well under half the cost of heating with oil or propane (or resistance electricity, at 15-20 cents/kwh.)

But I don't know anybody in MA living in a barely insulated ~1450' house off the gas grid who is spending less than $500/month during the winter in heating fuel + electricity to stay warm in January. With a mini-split in a municipal owned utility town with low-cost electricity, or somebody who cuts & splits their own cordwood could probably duck under that bar...

I exaggerated a little bit.  She is on the gird.  She lives in Lexington.  I really want to say that she doesn't live in a super insulated house.  She did replace the windows I believe a couple of years ago, but mostly it is the same home from 45 years ago.  I am pretty sure she doesn't pay $500/month on utilities.  My point is that when someone says that they are saving x dollars based on something, it is almost a much higher number to make themselves feel better.  I think going from a code minimum house at ~2000 sq ft to a super insulated house, it would be impossible to save $500/month on utilities.  Maybe, if they compare to a house with the windows opened all of the time, and during the winter they have the house at 78 degrees, and in the summer they still have the windows and doors open, and they are trying to cool to 60 degrees, compared to keeping their super insulated house at a normal temperature with the doors and windows closed, maybe, you could get $500/month difference.

Posted By Dana1 on 25 Aug 2014 05:38 PM

Posted By eugenep on 24 Aug 2014 04:11 PM

Posted By ICFHybrid on 23 Aug 2014 10:45 AM

I think that $330,000 for that house is pretty expensive

The house you are referring to didn't cost $330,000. It sold for $195,200, which included the land and builder profit. What it says in the article is that Mr. Scott's company plans to build a number of other very efficient homes, some with 4 bedrooms that will sell for up to $330,000.

You could easily build a much larger house for less using a normal hvac system

That's the same greedy thinking that has caused the very problem people are trying to solve. A major tenet of Green Building is to build homes that don't waste energy just because it is unaccountably cheap. BTW, Carter Scott notes that a "normal" HVAC system for this house would have cost his company about $14,000 and they did this one for $7,500, or about half. Building more efficient envelopes pays off in terms of spending less on the heating plant to begin with.

I don't think most people are looking at a 2-story that small.

That's exactly the kind of home a number of new families are looking at, as well as a number of older couples where the kids have moved out and the parents are looking to downsize. The difference might be in the level of finish afforded. A nice feature of the energy-efficient homes for both couples starting out and for retiring couples is that the energy costs are more predictable and controllable, making it easier on budgets.

In one town, the houses start at $330,000.   Of course, you picked the town which says they go up to $330,000.  Whatever.  They don't specify the size.  It isn't greed.  It is the the concept of diminishing returns.  He is putting 17kw on some of these houses.  They probably only need 2kw.  It doesn't make sense.

I found a few more articles about his homes, and they say they are saving $500/month in utilities.  My sister who lives in Massachusetts in the crappiest house in the world with hardly any insulation, wet basement, minimum attic insulation, 2 story house with a basement, doesn't use $500/month in utilities, so it would be impossible to save that much/month.  Her house is 1450 sq ft and 45 years old.

So, I am doubtful of most of the numbers that people quote.  Maybe, he gave us his highest quote that he wouldn't use.  Who knows.

I don't think most older people want to buy a small 2 story house.  Maybe, in your part of the world, but most people say when they get older, they don't want to climb steps.

Carter Scott's typical Net Zero Energy houses have between 5-10KW of PV on them- the 17KW example is an outlier. (Trying to cover the pool heating energy too, mayhaps? ) 

I've never met anybody  in MA who could heat & light their house on the annual output of 2KW of PV array- that would barely cover the annual lighting & entertainment equipment loads at my house (even if I DIDN'T have the limiting shading factors), and wouldn't come close to covering the heating & cooling loads even with the best-in-class heat pumps.

Your sister apparently is not heating with #2 oil or propane in the crappiest 1450' house in Massachusetts. Plenty people in central MA living in 1200-1500' 1960s vintage houses with R19-R30 in the attic and at least R11 in the walls are spending more than $3000/year just on heating oil or propane, and another $1000/year on electricity. (I know several of those people personally.)

In the same area people are living in ~3000' 2x4 framed houses with no wall insulation (none!) and at best  R19 in the attic, heat the place with 70% efficiency steam boilers and pay maybe $400 on the coldest month for heating, and maybe $2000/year total, by virtue of being on the gas grid. (I know several of those people too.)

Those living off the gas grid have quite a bit more financial incentive to go with high-performance houses & heat pumps, given that propane and oil BTUs cost about 3x as much as natural gas at local grid pricing. The marginal cost of ductless heat pump BTUs is cheaper than 70% efficeincy gas, but more expensive than condensing gas, but still well under half the cost of heating with oil or propane (or resistance electricity, at 15-20 cents/kwh.)

But I don't know anybody in MA living in a barely insulated ~1450' house off the gas grid who is spending less than $500/month during the winter in heating fuel + electricity to stay warm in January. With a mini-split in a municipal owned utility town with low-cost electricity, or somebody who cuts & splits their own cordwood could probably duck under that bar...

even your bad case is only $4000/yr, so how can someone save $6000/yr when you believe these bad homes are only paying $4000/yr.

You can doubt all you want, but here is another article about Carter Scott.

Maybe you didn't see that the "extra" solar produced is enough to power a couple of EVs for the year.

Posted By ICFHybrid on 25 Aug 2014 10:53 PM

You can doubt all you want, but here is another article about Carter Scott.

Maybe you didn't see that the "extra" solar produced is enough to power a couple of EVs for the year.

i am not sure of your point.

i am not sure of your point.

If you read the articles, you will see that these are experiments, designed to explore the parameters of building these kinds of homes. Maybe you didn't realize that there are people who actively resist Green Building. It commonly comes from ignorance. One of the things I heard locally was that homes can't support enough PV panels to provide self-sufficiency, Obviously, with a combination of attention paid to insulation, heating efficiency and design, not only can it be done, but it is possible to produce enough power to support the driving needs of the household as well.

Posted By ICFHybrid on 26 Aug 2014 09:26 AM

i am not sure of your point.

If you read the articles, you will see that these are experiments, designed to explore the parameters of building these kinds of homes. Maybe you didn't realize that there are people who actively resist Green Building. It commonly comes from ignorance. One of the things I heard locally was that homes can't support enough PV panels to provide self-sufficiency, Obviously, with a combination of attention paid to insulation, heating efficiency and design, not only can it be done, but it is possible to produce enough power to support the driving needs of the household as well.

i guess he took down his data, and then tore the houses down, so that he could run another experiment.

i guess he took down his data, and then tore the houses down, so that he could run another experiment.

You'd have to show us what part of the articles indicate the houses were torn down upon completion.