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Thermally Efficient Home


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#1 Farming guy

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Posted 21 September 2017 - 05:22 PM

I've had the idea kicking around in my head that one day I would like to build a super energy efficient home, and for several years I have thought about either building a house within a greenhouse, or a house attached to a greenhouse with a heat pump in between.  

 

Has anyone here seen something like this?  Which way would be better?  Any ideas for the pros and cons of such construction?

 

 



#2 DrKrettin

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Posted 22 September 2017 - 04:20 AM

That sounds like a good idea. I imagine that the house within a greenhouse would either be very small or prohibitively expensive. Linking up a house to a greenhouse sounds much more realistic, and not such a large commitment to a project which might not work. What kind of temperature is it in the greenhouse in winter, when the heat requirement in the house would be a maximum? Would the heat pump cool the greenhouse, and if so, would it have a thermal capacity large enough to cope with it?



#3 exchemist

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Posted 22 September 2017 - 07:49 AM

I've had the idea kicking around in my head that one day I would like to build a super energy efficient home, and for several years I have thought about either building a house within a greenhouse, or a house attached to a greenhouse with a heat pump in between.  

 

Has anyone here seen something like this?  Which way would be better?  Any ideas for the pros and cons of such construction?

I'm not sure I understand the principle here. Are you seeing the greenhouse as a source of heat for energy? Doesn't that mean you end up cooling the greenhouse and, if so, does that matter? (Here in the UK the greenhouse has to get hotter than ambient, to enable us to grow things from a Mediterranean climate, so we wouldn't want to extract heat from it.) 



#4 Farming guy

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Posted 22 September 2017 - 03:51 PM

That sounds like a good idea. I imagine that the house within a greenhouse would either be very small or prohibitively expensive.

I like the idea of a tiny house, but doubt I could sell my wife on that idea. I suppose the ideal house size would be big enough to entertain guests, but not so big that they will want to stay.  You can buy inexpensive greenhouses through a catalog that have a metal tube arch that you pull a clear plastic cover over top.  Some have an inflatable roof.   They can either be anchored with a large auger type screw in the ground, concrete piers, or you can spend the big bucks and build a full concrete foundation.

 

I'm not sure I understand the principle here. Are you seeing the greenhouse as a source of heat for energy? Doesn't that mean you end up cooling the greenhouse and, if so, does that matter? (Here in the UK the greenhouse has to get hotter than ambient, to enable us to grow things from a Mediterranean climate, so we wouldn't want to extract heat from it.) 

The primary goal  of the greenhouse is to provide cheap heat for the house, but I suppose it would be possible to grow a winter wheat, rye, or oats or triticale that don't require warm temperatures to thrive.

 

In warmer times of the year, you would want to pull a shade cloth over the greenhouse to keep things cool.



#5 JMJones0424

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Posted 22 September 2017 - 10:52 PM

In order to answer your question effectively, we need to know your climate.  High thermal mass homes work great in relatively extreme latitudes where the structure stores solar energy during the day and releases it during the night.  As you get into warmer climates, you no longer desire thermal mass, instead the goal is to efficiently insulate the living area from the predominately warmer exterior and therefore thermal mass is undesirable.

 

In most climates, the most efficient solution is to live underground.  Few people find this desirable, though.

 

Greenhouses, even in colder climates, are excellent environments for growing plants, but they are decidedly not ideal for human habitation.  Warm, humid conditions are not ideal for human health.  If I lived in a greenhouse, I'd want far more fresh air circulation than plants require.  I frequently work in greenhouses and find them stifling.  Perhaps what you actually are looking for is a solar thermal home (assuming you are in a climate where heating is the major concern).  Fortunately for you, moderating low temperatures seems to be far easier than moderating high temperatures.

 

Assuming you are trying to moderate low temperature, I suggest that you research rammed-earth construction techniques and other constructions that incorporate solar thermal storage.  Other alternatives are earth bags, adobe bricks, concrete, structural brick, or any other high mass building material.  These types of materials are poor insulators, but they are great at storing solar heat and radiating that heat during the night.

 

In a warm environment like I live in, I have to avoid these materials and instead choose low mass building materials and thick insulation in order to prevent solar energy from overheating my living space.  In a warm environment, straw-bale walls, conventional stick-frame or pole-barn with thick insulated walls, and false roofs and wide overhangs are more beneficial.

 

Fundamentally, your construction material choice has to be made around whether you are trying to store solar energy or protect against solar energy.  Regardless, I would never recommend building a home within anything like a greenhouse.  High humidity is not desirable for a living space.  Any organic material in a high humidity environment will rot and promote mold growth, which will adversely affect your health.  Leave the greenhouse to the plants and construct a home that appropriately utilizes solar energy without the downsides of greenhouses.  Use a heat pump to transfer heat to or from the ground without dealing with the humidity issues of a greenhouse.


Edited by JMJones0424, 23 September 2017 - 12:15 AM.


#6 Farming guy

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Posted 23 September 2017 - 04:21 AM

Humidity is a factor that I had failed to consider!  Thank you JMJones!

 

It gets cold where I live, although the last couple of winters it didn't get to -20 degrees F, but I do recall a time or two when the early morning temperature hit -30.  I have also had the idea of just putting up a south facing porch with a glass wall, and putting in some sort of solar heat collector that could store and radiate heat at night.  (I live in the Northeast US)  



#7 DrKrettin

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Posted 23 September 2017 - 05:56 AM

I was going to ask about humidity as well, because I have the opposite problem of how to cool our house in summer. I have excavated a cave a few metres away from the house which is wonderfully cool, and was wondering how I could use this to cool the house, whether I could pump air into the house from the cave, something like that. The humidity of the air from the cave is something which is putting me off, because I suspect it could bring problems (without my knowing exactly why). There is also the unlikely but lingering possibility of harmful gases sucked out of the cave, carbon dioxide for example. There are caves not far away which are deadly because of this.

 

Your idea of a house inside the greenhouse also has an equivalent for me, because I was considering a structure over the house to prevent direct sunlight on the roof, which acts as a heat reservoir. I've dismissed this as too expensive, apart from planning permission issues.



#8 Farming guy

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Posted 25 September 2017 - 01:05 PM

I was going to ask about humidity as well, because I have the opposite problem of how to cool our house in summer. I have excavated a cave a few metres away from the house which is wonderfully cool, and was wondering how I could use this to cool the house, whether I could pump air into the house from the cave, something like that. The humidity of the air from the cave is something which is putting me off, because I suspect it could bring problems (without my knowing exactly why). There is also the unlikely but lingering possibility of harmful gases sucked out of the cave, carbon dioxide for example. There are caves not far away which are deadly because of this.

 

One possibility for your situation would be to  put an air intake of some sort outside of the cave to draw in fresh air from outside, and run the air through a heat exchanger in the cave and run some duct work underground into your house..



#9 DrKrettin

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Posted 26 September 2017 - 12:38 AM

One possibility for your situation would be to  put an air intake of some sort outside of the cave to draw in fresh air from outside, and run the air through a heat exchanger in the cave and run some duct work underground into your house..

 

That's a nice simple idea, and I'll think hard about it. You would not use the word "underground" if you knew how impossible that is when you live on a volcano. Nothing is underground (except my cave), not even mains water pipes. But I don't want to hijack your thread.


Edited by DrKrettin, 26 September 2017 - 12:38 AM.


#10 Farming guy

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Posted 26 September 2017 - 04:08 AM

That's a nice simple idea, and I'll think hard about it. You would not use the word "underground" if you knew how impossible that is when you live on a volcano. Nothing is underground (except my cave), not even mains water pipes. But I don't want to hijack your thread.

I have a great love of simplicity.  No volcanoes where I live, but in some places we have granite.  When the road by the farm was rebuilt, they dug down below the frost line to build the base, and they used a lot of dynamite!  I don't suppose your neighbors would like you blasting a trench.  It's too bad, because soil is a good insulator.  If you have to run the duct work overground, you will obviously want to insulate it well.  Perhaps you could build a raised bed and grow a garden on top of it?



#11 DrKrettin

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Posted 26 September 2017 - 06:42 AM

I have a great love of simplicity.  No volcanoes where I live, but in some places we have granite.  When the road by the farm was rebuilt, they dug down below the frost line to build the base, and they used a lot of dynamite!  I don't suppose your neighbors would like you blasting a trench.  It's too bad, because soil is a good insulator.  If you have to run the duct work overground, you will obviously want to insulate it well.  Perhaps you could build a raised bed and grow a garden on top of it?

 

Nah, there's no way  I could bury the pipes, and explosives are unobtainable (Europe being an extremely dangerous place, as we have been told). They would have to be large diameter pipes and a lot of insulation, making it quite expensive as well as very unattractive. More thought needed.


Edited by DrKrettin, 26 September 2017 - 06:42 AM.


#12 Farming guy

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Posted 26 September 2017 - 07:28 AM

Nah, there's no way  I could bury the pipes, and explosives are unobtainable (Europe being an extremely dangerous place, as we have been told). They would have to be large diameter pipes and a lot of insulation, making it quite expensive as well as very unattractive. More thought needed.

It looks like the more practical method for you would be to use a heat pump.  In my area there are companies advertising heat pumps for both heating and cooling, although I am skeptical about their effectiveness under more extreme weather conditions.



#13 exchemist

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Posted 26 September 2017 - 07:54 AM

It looks like the more practical method for you would be to use a heat pump.  In my area there are companies advertising heat pumps for both heating and cooling, although I am skeptical about their effectiveness under more extreme weather conditions.

If you do that you will of course heat the cave up. What you are doing in effect is installing air conditioning in the house, and rejecting the heat extracted into the cave. Which will save on electricity compared to rejecting the heat into the ambient air, but at the cost of losing the coolness of the cave. My guess would be that the cave is only cool because it has a large "thermal mass" and therefore averages night and day, even possibly winter and summer. If you introduce a heat source that may be lost.  


Edited by exchemist, 26 September 2017 - 07:56 AM.


#14 DrKrettin

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Posted 26 September 2017 - 09:11 AM

If you do that you will of course heat the cave up. What you are doing in effect is installing air conditioning in the house, and rejecting the heat extracted into the cave. Which will save on electricity compared to rejecting the heat into the ambient air, but at the cost of losing the coolness of the cave. My guess would be that the cave is only cool because it has a large "thermal mass" and therefore averages night and day, even possibly winter and summer. If you introduce a heat source that may be lost.  

 

Yes, of course. But heating up the cave is an acceptable loss if it cools the bedroom. When there is a heat wave, the temperature in the bedroom can be around 36 degrees, and it takes some getting used to, plus plenty of wine. I've tried sleeping in the cave, but can't get used to the intense silence, and the wife won't use it (which would certainly solve the silence problem) because the access is difficult and (shock horror) it has no bathroom.



#15 exchemist

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Posted 26 September 2017 - 09:18 AM

Yes, of course. But heating up the cave is an acceptable loss if it cools the bedroom. When there is a heat wave, the temperature in the bedroom can be around 36 degrees, and it takes some getting used to, plus plenty of wine. I've tried sleeping in the cave, but can't get used to the intense silence, and the wife won't use it (which would certainly solve the silence problem) because the access is difficult and (shock horror) it has no bathroom.

Yes I recall the challenge, from my time in Dubai and then again in Houston TX. Like you perhaps I resisted the temptation to run AC all the time, as I thought it better to adapt as far as possible. (In DXB, people who used a lot of AC always seemed to have colds.) But in both places, I did resort to an hour of AC to cool the bedroom before turning in. Are you not better off just to do the conventional thing and get an AC unit fitted in your bedroom, plus maybe a ceiling fan, rather than all these pipes to the cave etc.? Or would that offend your sense of waste?   



#16 DrKrettin

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Posted 26 September 2017 - 09:45 AM

Yes I recall the challenge, from my time in Dubai and then again in Houston TX. Like you perhaps I resisted the temptation to run AC all the time, as I thought it better to adapt as far as possible. (In DXB, people who used a lot of AC always seemed to have colds.) But in both places, I did resort to an hour of AC to cool the bedroom before turning in. Are you not better off just to do the conventional thing and get an AC unit fitted in your bedroom, plus maybe a ceiling fan, rather than all these pipes to the cave etc.? Or would that offend your sense of waste?   

 

The annoying thing is that we tried Air Conditioning in the bedroom (I typed AC in the bedroom, but that sounded kinky) and it was ineffective. It's a small house with a wooden roof with a concrete layer on top, covered with tiles, and the bedroom is just a mezzanine immediately below it. With a week's worth of direct sunlight on the roof, it acts as a heat radiator at night, so no amount of freezing air from the AC had any effect apart from giving us sore throats.** So you may ask what the point of cool air from the cave might be. I was thinking possible large amounts of cool air would be better than cold from the AC.

 

My other idea was to install a water spray directly onto the tiles of the roof to prevent it heating up, but the water is metered and not cheap, plus the residue from evaporated water might might a mess. All in all, I'm rather stumped.

 

** so a ceiling fan would just draw hot air down. I have installed a powerful fan which blows air sideways into the bedroom, having removed all the security grills to make it very quiet.


Edited by DrKrettin, 26 September 2017 - 09:47 AM.


#17 exchemist

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Posted 26 September 2017 - 09:52 AM

The annoying thing is that we tried Air Conditioning in the bedroom (I typed AC in the bedroom, but that sounded kinky) and it was ineffective. It's a small house with a wooden roof with a concrete layer on top, covered with tiles, and the bedroom is just a mezzanine immediately below it. With a week's worth of direct sunlight on the roof, it acts as a heat radiator at night, so no amount of freezing air from the AC had any effect apart from giving us sore throats.** So you may ask what the point of cool air from the cave might be. I was thinking possible large amounts of cool air would be better than cold from the AC.

 

My other idea was to install a water spray directly onto the tiles of the roof to prevent it heating up, but the water is metered and not cheap, plus the residue from evaporated water might might a mess. All in all, I'm rather stumped.

 

** so a ceiling fan would just draw hot air down. I have installed a powerful fan which blows air sideways into the bedroom, having removed all the security grills to make it very quiet.

Reflective film over the roof? And maybe some insulation tiles on the ceiling?