Boxed heat pump

[Telco]

I'm ramping up the initial design phase for building a new high efficiency house, to begin in about 2 years. While considering the heat pump, got an idea about how to conserve winter heat with one. I have no idea if this would work or if it's competely off the wall but...

Since a heat pump draws heat from the air, and there isn't a lot of heat outside in winter, seems like building a box to go around the heat pump might help. Said box would draw heat from the motor spinning the blades. Not a lot there, I know. The box would also have a glass roof to collect sunlight. Even in winter, sunlight shining through glass into an enclosed area makes a lot of heat. This should make it easier for the heat pump to extract heat from the air and make it cheaper to heat the house. This would not work at night, of course, and the box would need to be removed in the summertime. This setup would also protect the heat pump from being stuffed full of snow in a storm. For summer, a simple sun/rain shade would be needed to keep direct sunlight from heating the unit.

Comments? Was thinking that a high efficiency heat pump might benefit from something like this.

[88HF]

??? My mom's house uses a water-source heat pump for the a/c. The well sources 1000ft. depth water and brings it up to cool the air in the house. Works really well, efficiently. Bad thing is the heat pump cost 4,000 and has to be shipped in from Fla. As far as heating, you could do one of those roof solar water heaters. Hell any kind of hose on the roof with water running through it in closed loop will heat really fast (unless its covered in snow). Then again, it might even melt a good bit of snow. You could always transfer the heat collected from a solar water htr to your a/c by putting the water through a radiator and having the blower push air through the radiator.

[Hockey4mnhs]

we have berm home you might want to consider one of them for your house.

[Snax]

A ground source heat pump is the only way to go. I can envision lots of problems with the box idea that I have had too many beers to articulate right now. ;)

[WisJim]

Unless you are in the tropics and "need" air conditioning, a heat pump for heating is a waste, in my opinion. A well insulated house, properly weather tight, with modest southern glass for passive heating, doesn't need much additional heating at all. Body heat and waste heat from lights and appliances is enough. An efficient small wood burning boiler with active solar and in-floor radiant heat will take care of heating needs, and the small pumps can be run by a small solar electric system.

Where are you located?

[koinos]

I don't think it is a good idea, I mean a heat pump. I can't say about "boxed". A "boxed" will be different issue. Anybody have any example of heat pump for a house heating or any other house application?

[Telco]

I'm in the Tulsa OK area. Summers average around 100 degrees, winters usually stay in the 40s but we do have weeklong snaps into single digits most years anymore.

Was very strong on ground loop heat pumps until I spoke with a fellow down in Louisiana who is an HVAC installer. He adv that the most common problem with these things is the loop breaking within 5 years. While there is a 50 year warranty on the loop piping, the warranty only covers materials, not labor. The pipes have to be "glued" into place with a special cement that promotes heat transfer, and is a major pain to get back out. Said that when the customers found out what this "warranty" repair was going to cost, they opted to get rid of the ground loop system in favor of a high SEER heat pump. Thinking this is the way I'm going to go with mine when the time comes. Going to try and stay away from wood burning stoves since burning wood puts pollution back into the air and requires my lazy butt and an axe in the "back forty." I won't rule it out, but going to try and stay away from it.

My dad runs a heat pump in his house 18 year old house, 1500 sq ft and only a little better insulated than my disaster, I mean just over 2 year old brand new house with 1750 sq ft. He keeps his place toasty in the winter and frigid in the summer, and has about a 100 dollar a month electric bill year round. He does live by himself, but does absolutely nothing to save energy. With a conventional air conditioner and gas fired furnace, I have a 130 dollar a month electric bill in summer and a 60 dollar winter electric bill, AND have a 50 dollar a month gas bill in summer and a 300 dollar a month gas bill in winter. My house is kept warm enough in summer than any activity will bring a sweat, and in the winter the house is cold enough that everyone has to wear sweaters and warm pants, and are constantly complaining how cold it is. I'm absolutely sold on heat pumps, wish I'd have made the deal dependent on them installing one when I bought the house. I know it isn't just the system though, there's also that Pop's house has all 8-9 ft ceilings, and over half of mine is cathedral ceilings. Never will I even look at a house with cathedral ceilings again, worst design for a house I've ever had the displeasure to live in.

No berm-style house for me. Don't want to mess with mowing the roof :D . I have about 2 years to finalize a design so there's no hurry.

[Bill in Houston]

I dunno. I guess putting the heat pump into a little greenhouse thingy might help. But isn't a heat pump relatively expensive when gas is available?

When you make your own house definitely spend the money to insulate it really well. And consider having a little vestibule/mud room at the entrance you will use most often to keep so much hot or cold air from escaping when you come into the house.

[Telco]

I dunno. I guess putting the heat pump into a little greenhouse thingy might help. But isn't a heat pump relatively expensive when gas is available?

Boy you'd think so, and this used to be the case, especially in Oklahoma. Prices spiked hard around 1999 - 2000, the price went up almost 700 percent overnight. Since then, a heat pump looks to be the most fuel efficient way to heat and cool a well insulated house, not that I've had one recently.

On top of this, I plan to live in the sticks, so gas would have to be trucked out. I'd far rather buy a few extra PV panels and maybe an extra windmill and run a heat pump than use gas. Gotta figure out a way to manage drying clothes too, a clothes dryer will take a lot of panels to run. I may wind up having to have LP when it comes down to it, but I really, really want to avoid it if I can. Clothes line will not be doable since the wife and I both work, then there's wintertime to think of.

When you make your own house definitely spend the money to insulate it really well. And consider having a little vestibule/mud room at the entrance you will use most often to keep so much hot or cold air from escaping when you come into the house.

Excellent idea. And for the summer, there will be an attic fan. A strong attic fan will generate a breeze through the whole house, which is wonderful when outside temps are between 60 and 90 degrees. After that would have to be air conditioned.

[Bill in Houston]

And for the summer, there will be an attic fan. A strong attic fan will generate a breeze through the whole house, which is wonderful when outside temps are between 60 and 90 degrees. After that would have to be air conditioned.With your relatively low humidity and the way it actually cools off some at night there, you will be able to save a lot with the attic fan. We had one in Denver and it was great.

[WisJim]

When we built a new house in the 1970s, we superinsulated it, and we used a couple of face cords of wood each winter to heat it. As I mentioned before, there is no substitute for good insulation and proper weathertiteness in a house. You don't need lots of expensive equipment to heat the place if you insulate, seal, and ventilate properly.

[Snax]

You also don't need expensive cooling with the same planning.

One of my favorite concepts is a foundation heat storage bank. Adequately sized and insulated from the surrounding ground, a large mass of sand can be used to store up heat in the late cooling season for later return in the heating season and vice-versa. Heating is provided by solar panels and a closed loop water/coolant circuit. And because the ground temperature surrounding the foundation is below normal household cooling temperature, there is no system required to cool the mass itself, as the extraction of heat through the winter is enough to provide cool mass through most of the summer.

[Ryland]

You also don't need expensive cooling with the same planning.

One of my favorite concepts is a foundation heat storage bank. Adequately sized and insulated from the surrounding ground, a large mass of sand can be used to store up heat in the late cooling season for later return in the heating season and vice-versa. Heating is provided by solar panels and a closed loop water/coolant circuit. And because the ground temperature surrounding the foundation is below normal household cooling temperature, there is no system required to cool the mass itself, as the extraction of heat through the winter is enough to provide cool mass through most of the summer.

When I was building energy efficent houses that is the basic concept that we used, use solar hot water panals to heat a mass of sand under your concreat slab, insulate that slab, and the ground around the slab, and around augest or september you turn on the hot water panals to start heating the floor, and turn them off around april, that mass stays warm, and by the time it's cooled off in the spring, it's starting to keep your house cool, even if you leave home for a few weeks in the dead of winter a system like this will keep your house 65-70 degrees, like was said befor the heat from cooking, having lights on, and other parts of daily life help keep it warm, and if that is not enough you design the system with propane or natural gas back up for those that don't like to clean the twigs out of their yard, as that is about as much wood at some of the houses I've worked on use, a pickup truck load of small firewood and kindling.

I spoke a while back to an enegner about heat pumps, and he basicly said that a single family home is too small, that they will cycle on and off to much, and that they don't operate efficently when cycling on and off like that, that the best use for them would be a multi family appartment building, or office building, not a house.

[Telco]

Very interesting. So how large a sandbox do you need for this? Any links that describe it in more detail, like maybe with pics and efficiency reports?

[Snax]

I believe that a more industry standard term for it is High-mass Solar Heating. In 'Solar Water Heating: A Comprehensive Guide to Solar Water and Space Heating Systems' (http://www.amazon.com/Solar-Water-Heating-Comprehensive-Systems/dp/0865715610), the author suggests 10.5 tons per 100 sq ft of space (or about 2' deep under the foundation).

I highly recommend that book.

[Telco]

Excellent, thanks! Mother Earth is an excellent resource.

Sweet! Did a search on "High-mass Solar Heating", and came up with this site. (http://www.thenaturalhome.com/passivesolar.html) Methinks I need to start rethinking my overall design now. Better now than 3 years from now, eh? :D

[Ryland]

most of the houses that I worked on had a vapor barrier, 2" or more of foam, and 12" of sand, one house was built on an old foundation with part of the basment filled with 6 feet of sand and hot water tubes in the bottem, and in the middle, that was over kill and altho it never got cold, it never got really warm either, 1 to 2 feet of sand seens reasonable, and putting the hot water tubes in the sand not the concreat gets rid of hot spots, and reduces the chance of the tubes cracking if the slab shifts.

[Telco]

Hmm, looks like my boxed heat pump idea may not be a bad idea. This site (http://www.dulley.com/docs/f442.htm) describes a solar heater for a window that is kind of what I had in mind for a preheater for a heat pump. Essentially what I was looking at was a greenhouse for the heat pump, let the sun heat the air inside the enclosure, then let the heat pump extract that heat to warm the inside of the house. The main problem with a heat pump is it is always working against the outside, it is either trying to extract heat from cold air or push heat into hot air, this would at least help with the wintertime part of it.

[theCase]

I've got mixed feelings about a boxed-in heat-pump. I can understand the idea of preheating the air surrounding the heat pump making it work better, but remember a H/P would rapidly cool down any enclosed space it is in. If the space is too small isn't it possible that a H/P could drop the temp in the space below ambient causing the H/P to be less efficient than just being outside?

Obvious factors affecting this would be the climate, size and mass of the enclosed area, duty cycles, etc. How about a large cheap plastic open-ended lean-to covering the H/P on the south side of the house? maybe?

And here's a great link covering lots of DIY solar projects.

http://www.builditsolar.com/

Good luck!

[Telco]

Yeah, I was thinking about the heat pump depleting all the heat too. It would have to be a fair sized cover for it, yet not so large that the cover never gets warmed up. Guess it will need an engineer to come up with what size that cover would need to be to allow the heat pump to get a boost. If the cover could retain enough heat when the compressor were off that it was still warmer inside the cover when the compressor cycled off though, it would save energy having the cover vs not having it, even if it were only 1 degree warmer.

Thanks, I'll dig around on that solar website. I plan to start building a new house in about 2 years, and if at all possible I want it to be offgrid, with the backup generator doing nothing but gathering dust between monthly maintenance test runs.

[Snax]

One thing to keep in mind about this idea is that air is a horrible medium for heat storage. It doesn't really hold much heat, and it readily releases and absorbs it. The heat pump would exhaust the stored heat energy in the surrounding air as quickly as it would the transfer that heat to the same volume of inside air which doesn't really count for much since it's the ambient temperature of the structure and what it contains that really needs to be affected, thus a more dense mass for storage would be far more effective.

[Telco]

Even so, it would have a 1 time cost, and any heat that could be pulled would be free. Was also kinda playing with the idea of a solar water heater for the house, could run the line from the solar heater through the heat pump's little hut, and have a radiator to add extra heat to it.

I know these are off the wall ideas, but perhaps from the BS I spread on this topic an actual good idea may grow :D.

So far as the house goes, was looking at a metal building with an inner shell house, with a ton of insulation in the middle. Now I'm kinda looking at doing a passive solar house with high thermal mass, (http://www.thenaturalhome.com) building the place out of cement with a nice, thick floor. One thing I really like about this site's ideas in particular is building the house larger than I intended, and having an indoor garden area for year round fruits and veggies. The wife is always trying to grow stuff in the house anyway, might as well build a larger area suited for it and get some real use (and food cost savings) out of it. Would be nice to need a tomato for dinner, and just step from the kitchen's cooking area to the garden to pull one off the vine without having to go outside, or even better doing this in December. And, by doing this dry stack cinder block (http://www.thenaturalhome.com/drystackblock.htm) build method, I'd save even more since stacking blocks and filling them with concrete is something anyone can do.

[Telco]

If anyone wants to try this idea of enclosing their heat pump I'd be interested in hearing the results. While researching alternative heating and cooling methods, I found that another possibility would be to build a Tromb wall inside a fixed enclosure for the heat pump. A Tromb wall would provide a more stable, radiant heat for the heat pump to draw on, which would effectively make the heat pump a solar pump. From what I've found, a Tromb wall can raise the temperature inside a small enclosure to some 160 degrees or more. Surely the heat pump wouldn't be able to pump all that out of the air before the house was warm enough, and the wall could recharge between pumping sessions. A thick enough wall would also store heat during the day for night time use, for even more savings. It would require that the heat pump's enclosure be permanent and well planned though, you'd want a way to shut down the heat absorption in the summertime and just use the enclosure to supply shade to the heat pump. Best of all about this plan, there is no additional energy or expense required once the wall was installed, and really all you'd need is some cinder blocks, insulation, and the plans for a Tromb wall with a heat pump facing the south.

For myself though, I've decided to ditch the whole heat pump idea in favor of radiant heat. Been hammering the web pretty hard over the last few days, and I think I found the way forward. Looking at using an outbuilding with a solar water heater on it to heat a water/antifreeze mix, which will be stored in a heavily insulated tank. No idea on the correct sizing yet, but just for grins I'm saying 1000 gallons for now.

The water will be heated by a whole wall of heaters during the day, with a pump to circulate heat back into the house into the house's hot water heater. This should mean that my in-house water heater should effectively be just a hot water tank, although it will have heating elements inside to keep the temp from falling off too far.

The water from the heater will be pumped through a heat exchanger that will be connected to a water powered radiant water heater that will keep the interior of the house warm. This also frees up my design method. The reason for a heat exchanger is so that I can use the radiant heating system as an air conditioner of sorts as well. I still have to figure out that part of it.

Using this setup, with the pumps being run off solar panels, means I should be able to keep the whole house toasty using only the power of the sun. Of course there will be a diesel generator onsite for backup power, and the outbuilding will have a wood fired stove to heat the water when necessary, but I kinda think that it will only be necessary on the coldest days of the year. And, considering it'll cost approximately 8 grand, if not more, to install a high efficiency air exchange heat pump that will then require lots of electricity and lots of extra solar panels, I think that building a radiant heating system into the house as I go will make for a huge savings to both me and the environment. Not to mention I'll no longer be responsible for stinky coal fired power plants and brownouts!

Alternative water heater source (http://www.radiantec.com/contact/)
The outbuilding water heater (http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/collectors.htm)

[2TonJellyBean]

Telco, one thing you may want to keep in mind is that if you go super-insulated then radiant heated floors might not even feel warm. They won't have to give off many BTUs and you have to consider all the parasitic pumping losses (higher electrical bills), especially if the tubing is smaller and more restrictive.

For a superinsulated home, my preference would be panel rads with TRVs (except perhaps the kitchen and baths). The TRVs allow non-electrical room by room heat control and automatic compensation to prevent solar heat gain - it's a purely mechanical control.



I'd love to do what you're doing. My outer walls would be concrete, then continuous XPS inside that and then a wood structural frame inside that possibly insulated with Roxul (no VP because the XPS is it). With high performance windows. the heatloss would be pretty low, even in the Great White North (although this design would work in suth'rn climes as well). The key idea would be to prevent thermal bridging everywhere...

[Telco]

I may be calling a duck a goose here. When I say radiant heat, I'm speaking of those little water radiators that go along the wall at floor level. They would be inside the insulated shell. I'm not too big on the in-floor heaters, since a pipe breaking means pulling the flooring out where a radiator simply requires turning a valve, then replacing the offending unit. Older tech, yes, but still very effective.

The pump should be covered by solar. When you look at the cost of a high efficiency HVAC system on a new install, like 10-12 grand, I'm figuring that going this way won't cost very much more even when you take the extra solar panels that would be required into account. And worse comes to worse, a diesel generator can provide the power on those few days per year when there wouldn't be enough sun to provide power. Winters in the Midwest are pretty mild overall, we usually have no more than 2 really bad weeks.

[Snax]

Don't let the fear of pipes breaking hold you back from the idea of radiant floor heat. In a well tested and sealed system constructed of Pex tubing, there really is no known definate lifespan. So long as you don't damage it by drilling through it or something, the possibility for a properly constructed system to leak is virtually nil.

[Telco]

Hmm, interesting. How well does it handle weight? My intent is Pergo-style flooring throughout the house, except in maybe the master bedroom, with large throw rugs in the living room and other bedrooms. Mater bed also will have a king size waterbed, one of the ones that looks like a regular bed but has a single bladder for the water. I'd like to do throw rugs in all rooms due to my wife's allergies since throw rugs can be either cleaned outside with soap and water regularly, dry cleaned or replaced when needed. I've heard of nasty stories where a large, heavy piece of furniture has crushed the lines under the floor causing a nasty leak, but as I say they are stories and may not be true.

Also, what happens if there is a power loss and the piping freezes? With the radiant heaters along the wall I know I have the option of draining the lines in an emergency. Would suck to take a weeklong cruise in the Bahamas to come back to no heating system. If the water bed freezes the bladder will stretch to accommodate some, and has a built-in retaining wall to catch most of the water so leakage would be minimal, if any in the event of a freeze.