alternate heating and cooling

[muddstopper]

I know this is a firewood forum for discussing wood burning, but I dont belong to any forums where I can ask this type of question so I am hopeing someone here can comment on some questions I have about solar heating and cooling.

I am in the planning stage of building a new house. One of the things I want to do is eliminate as much electricity use as possible. I have some ideals on how to heat and cool the house using solar and I am going to throw this out there for discussion.

For cooling, I have access to a very good creek with lots of running water. Water temps are in the 55f to 60f range year round. My thoughts to take advantage of this cold water is to use a low voltage water pump and solar panel to circulate water from the creek to the house. There is about a 75ft elevation change from the creek up to the house site, but since the water would be in a closed loop system, it shouldnt take a lot of power to move the water. I will be installing a concrete tank at the creek to catch the cold water and something I can install a copper tube heat exchanger into. At each end of the heat exchanger I will be attaching pex tubing for the cooling system. The pump will pump water up to the house and thru another heat exchanger, either copper or aluminum, that is enclosed in a box. The box willl have a squirrel cage duct fan to blow air across the heat exchanger and into the house. I helped do this once with a loop of pipe in the ground, but the guy had problems with the soil becoming saturated by heat and the system stopped working. He had about 300ft of pipe just buried in the ground and the water in the pipe neutralized in temp differences. With a good continuing source of cold water, I dont think the water temp stored in the pipe will neutralize in my system.

My first concern would be heat loss of the pex tubing that is burried about 200ft to the house. Since soil temps below topsoil layer is typically also in the 55f to 60f range it shouldnt be a big problems, but the water temp going from the house will be slightly higher than the temp of the water going to the house. I have seen buried systems before that suffered from soil heat saturation because they where heating up the soil faster than it can cool. I dont think I will have that problems because I will have a constant flow of cold water running in the same ditch.

My second concern is the duct mounted heat exchanger condensing water and a possible mold problem in my duct work. I havent figured out how to combat that issue yet so any ideals or advice is welcome.

For heating, I have a unconventional ideal that may or may not work. I am not limited by lot space and am planning on having a solar hot water heater. I currently use my wood stove to heat my water, but that only works in the wintertime when I actually use my stove. I figure on having a solar water heater connected to my conventional electric water heater. I am thinking if I build a big enough collector, I could circulate some of that solar heated water thru my duct mounted heat exchanger and us the duct fan to put hot air thru the house. I am sure with a big enough solar collector and big hot water storage tank one could probably heat the entire house most of the winter, but my plans would be more modest and using the solar heater just to supplement my wood heat. See I aint trying to completely get away from wood heat

 

[svk]

This should be a great thread.

I don’t know much about this but I know thermopex loses very little temp per hundred feet.

 

[Mustang71]

How deep are u burying the pex? At 55 to 60 degrees you wont cool very quickly but it should work if you can keep that indoor coil temp at 55 degrees. With refrigeration, 410a, an indoor coil would run somewhere around 44 degrees at a 72 degree air temp. Now if you could run a low cost circ pump and a low cost blower motor all the time you hold a cool temp all summer.


They have some of those solar heating elements around here left over from the 70s and 1 person told me it worked good lol. Using solar to heat water would be a good supplement. Using solar to run an electric water heater might be a better heat sorce.

 

[ChoppyChoppy]

I'd think about pv panels and just use you existing water heater.

I have 18 panels on my roof, works well.

 

[Streblerm]

What your suggesting exists in water source heating and cooling. It is called a “water side economizer”. The idea is to use it when temperatures aren’t too high or in conjunction with the the refrigerant circuit to increase efficiency. They are very common in industrial cooling tower applications. I have read and heard of people using these with great success in residential geothermal. Of course I read and heard of people having great success with geothermal heating which wasn’t the case in my house.

From what I can tell they use large surface area heat exchangers with a condensate tray similar to a regular A-coil. There’s quite a bit of info out there. Most of it seems designed to sell a completed water side economizer but you may be able to glean some design info from some of the literature.


https://www.waterfurnace.com/literature/envision/sc1650ew.pdf

 

[Mustang71]

Cooling towers are used to remove the heat out of the building. The ones I've worked with were used to circulate water around the building to cool all the small heating/cooling refrigeration units with a boiler for heat pump purposes.

It's the same idea but I dont think he's going to be using refrigeration so it wont be the same effect. I think it would more like geothermal cooling. But you need to maintain that cool temp from the water to the coil in the house.

 

[Streblerm]

They are used with geothermal systems as well. It really doesn’t matter what the source of cool water is just that you have a source of cool water. Ground loop, body of water, well, cooling tower...the result is cool water. The water side economizer moves heat from the air into the cool water without the aid of refrigerant unlike traditional a/c which moves the heat into refrigerant.

In muddstopper’s system the stream fed cistern functions as his cooling tower. This makes all the data available on water side economizer useful in my mind. It will at least give you some guidelines as to capacity so you don’t have to start blind.

As far as loss of efficiency through the piping, I don’t think it will be a major issue as long as the ground temp where the pipe is buried is similar to the temperature of the water. If you are worried about the outgoing water affecting the incoming water temp then just make two trenches. 400’ of buried pex should do nothing but help.

 

[Mustang71]

It sounds like a great idea I just wonder how well it will work on a 90+ degree day with the house in full sun. I'm sure he will have some good insulation.

Might as well pipe an OWB into the loop.

 

[spyder62]

First I would have a heat gain/ loss calculation done so you know what size cooling coil you will need . Also blower and duct sizing. I’m also concerned about your water temp at the coil. 60 ain’t gonna cut it. What about solar panels powering conventional type cooling

 

[2412]

How is the creek water going to circulate through the concrete tank?

I know people that keep their wood fires burning all summer for hot water. I’ve also heard of using a large water tank for thermal storage, and firing once a day to get the storage up to temp.

 

[muddstopper]

Well, some of you are talking a little over my head, but thats ok, keep talking and I will learn a thing or two.
To answer one question, about how deep will I be buring the pex. My trencher will go 24in deep. Now I know you northernfolks have to go a lot deeper to keep from freezeing. Highest temps I have detected at that depth has been 60-62*f and that was in the middle of summer in really sandy soil, direct full sunlite. Clays, like I will be working in, tend to run a couple degrees cooler. I will be placing both pipes in the same ditch. Pex doesnt transfer heat very well and if it did, I think with a constant source of cold water running up on side would cancel out any effect of slightly warmer water running back down.

Getting the cold water to give up its cold is where I think my problems start. The previous system I helped with, the guy used the Atype heat exchanger out of an old heat pump. Using a low voltage water pump to circulate the water, he was only able to capture about 2degrees of that water temp. Measured going into the coil and measured out of the coil. While the air coming out of his ducts was a couple degrees colder than the air passing over the heat exchanger, The difference wasnt enough to really tell. I believe if he had of used more than just one of those A type heat exchangers, he would have been able to keep the air exposed longer to the cooler water and got a few more degrees of cooling. If you can get the air down to the 60 degree level off the exchangers, then keeping the house cool shouldnt be a problem. I shouldnt have a problem obtaining as many of those old Aframe style heat exchanger from old heat pump systems as I might want. Hvac places have them stacked out back just waiting to recycle. Now heres the catch, I am not convinced using old Aframe exchangers for cooling air is my best choice. I know they use single exchangers in Hvac, but they are using freon and producing a lot colder temps than I will be able to do just pumping cold water. Ideal system would be able to pump 60F water and 80F air into my exchanger, and get 80F water and 60F air out.

As for getting water into my cistern, it will be 24/7 piped in and out of the tank. This is another feature of my building plans. My creek has about 75ft of fall from where I plan to catch the water. I plan on a small hydrogenerator set up where I will be placing my cooling coil. The water coming out of the turbine will fill the tank for cooling and then overflow back into the creek. Keeping the cooling coil cold wont be a problem and efficiency wont be a factor as I dont expect the temp to vary much between water looped in and water looped out. If it doesnt cool the returning water enough, I will just add another coil. I spend a lot more cooling my house in the summer than I do heating in the winter. If I can get a system to work, then the payback would probably be less than a year. I know if I can get power bills in the winter in the $125 range a month and the bills jump to $225 a month in the summer, Thats a $100 a month anyway you look at it. If I can save even more a month using a little hydro electric, the saving start really getting serious. The hydroelectric is where cost start going up. Digging in 1000ft of pipe, buying the right generator setup, running wires, inverters, batteries, disconnects, it all makes my head spin and my billfold want to cry.

As for the solar heating, my main goal is to keep a steady supply of hot water. Personal experience tells me I spend about $50 a month just heating water. My main heat source is wood with a heatpump backup. My goal is to keep the heat pump and water heater not turned on. Having built and helping build a few solar water heaters, I know it doesnt take a lot of money to build a system that will heat water. The two main things one needs is surface area and storage. The more surface area you have the more water you can heat, and the hotter you can get it. If you are going to heat a lot of water you have to be able to store it. If you going to heat a house using solar heated water, you are going to need a lot of storage.

 

[Mustang71]

If I were to build a water coil I would use 3/4 base board and make it nice and big. I dont think a refrigeration coil will do much for water the capillary tubes are very small. The only time I have seen close to a 60 degree coil temp in HVAC was when it was 90 in the house and we just finished the install. I dont think it's possible to blow 80 degree air past a 60 degree coil and have the air leave at 60 degrees. I dont think it will really condensate either. With real good insulation and constant running of the system it might work ok. I wish you the best.

I do think your long pipe run will help cool down the out going water and I would go with a decent pump not a low voltage pump. A 3 speed taco brand pump might work.

It's all a cool idea to become self sufficient in a way and use a natural source for power.

If its 60 degrees 24 inches below the ground then y not dig a basement and circulate that air through out the house, it should stay about 60.

 

[muddstopper]

The system can run 24/7 if I need it to. There are low votage deep well pumps that will produce over 200ft of head. I need to keep the pump low voltage because I dont want to run high voltage 200ft. Altho in a closed loop system, I guess it dont really matter where the pump is located.

Basement is out of the question. Stairs are a no go.

As for the 80 in and 60 out, I said that would be ideal, but I do think it would be very hard to do. Exchanger coils in the tank isnt that hard to do. I have seen just coils of copper tubing just more or less dropped inside tanks work very well for heat exchangers. I guess it has more to do with the amount of surface area you have exposed to the cooling liquid that what the system looks like.

One other thing I am looking at is a chilled beam for cooling. https://en.wikipedia.org/wiki/Chilled_beam. I just found out about these systems and dont a lot about them yet. They are designed to cool by pumping cold water thru them and using natural convection. It sounds like a simple setup to do just what I want to do, but I dont have any ideal of cost or how to mount in a conventional house ceiling.

 

[spyder62]

If I were to build a water coil I would use 3/4 base board and make it nice and big. I dont think a refrigeration coil will do much for water the capillary tubes are very small. The only time I have seen close to a 60 degree coil temp in HVAC was when it was 90 in the house and we just finished the install. I dont think it's possible to blow 80 degree air past a 60 degree coil and have the air leave at 60 degrees. I dont think it will really condensate either. With real good insulation and constant running of the system it might work ok. I wish you the best.

I do think your long pipe run will help cool down the out going water and I would go with a decent pump not a low voltage pump. A 3 speed taco brand pump might work.

It's all a cool idea to become self sufficient in a way and use a natural source for power.

If its 60 degrees 24 inches below the ground then y not dig a basement and circulate that air through out the house, it should stay about 60.

I couldn’t agree more with what mike said. The chilled water systems I work on (cooling) are all running about 45 degree water. If you could deliver 55 degree water at the proper flow and the correct airflow through the proper coil it would probably work. On the hottest days when you need it most and the temp in the creek rises I think you will have problems.google chilled water coils. There is some good info

 

[muddstopper]

I think we may be on to something. The chilled water coil looks like a kissing cousin of the Chilled beam. Where as the chilled beam is meant to work by convection, the chilled coil is made for forced air. Chilled coils such as this one, http://www.dhtnet.com/products/chilled-water-coils/, are meant to be installed in your conventinal air handling system or in your duct work. This is what I had in mind.. Now the difference I see in the chilled coil and the used aframe heat exchangers from old heat pumps is the size of the tube in the coils. The difference I see in chilled beam design and chilled coils is lenght, versus thickness. Chilled beams are long and thin, chilled coils are compact and thick. Both seem to have similar surface areas.

Now I have just found out about these two types of systems, so I sure dont know all I need to know about them. From what I have read so far, the chilled coil would be the better of the two systems for my use. Mounted in the duct work, it would be the easiest to keep out of sight, and the easiest to switch over the a hot water heating system.
I still worry about condensation and the mold that could result from it. @spyder62 How do you deal with any mold issues, or is condensation even an issue.

 

[Mustang71]

That coil in your link has a plastic drain pan under it. It's for a vertical air handler you would need a different coil for horizontal application. For people who are concerned about mold they sell a uv light that can be mounted above the coil in the duct work that "kills" mold. I dont think mold is an issue.

That coil would work for heating and cooling.

 

[muddstopper]

I didnt see that drain pan, glad you pointed it out. With a pan and drain, I think one could probably hook up a sump pump that would pump any water, that might accumulate from condensation, outside just like my current heat pump uses.

I have noticed several different configuations of the chilled coil for duct work applications. I wonder if there is any advantage of using one like this, http://www.dhtnet.com/products/water-coils/ over the Aframe type in my first link.

 

[4seasons]

I just skimmed through most of these posts but I didn't see the key answer to the problem of using 60° water to cool a house. That answer is volume. If you think about it for heating with fire like we are all familiar with, you have a small firebox, say 4 cubic feet, and are heating 10,000 cubic feet. But because the firebox is 500° it can pull the 40° difference between freezing outside up to 70-80° inside. But you are talking about a 470° temperature difference.
On the cooling side if you are using the same math, in order to use 60° water to cool in 90° weather, you would need 10,000 cubic feet of water to reach 75°. Of course good insulation will help, but you still need way more heat exchange that your typical A/C coils that run close to 35°.
Have you thought about using long loops of pipes in the floor like some use for radiant heat with a boiler.

Sent from my XT1254 using Tapatalk

 

[muddstopper]

I think I am formulating a plan on how to make what I want, to actually work.

First thing I see as a disadvantage of using a creek water cooled system for air conditioning and solar heated water for heating is actually changing the temp inside the house if it is extremly hot or cold inside. I think using solar heated water would be very slow in warming up a very cold house, and cooling a hot house would take a equally long time using the cold water system. I also believe that once the house is at the desired temp, maintain that temp shouldnt be that hard to do using solar heating and water cooling.

I dont plan on being totally off grid and will have a heat pump as well as a electric hotwater heater. If I install a chilling coil in the return air side of a normal forced air system I should be able to cool or heat the air before it reaches the heat pump. This way I would have the benefit of instant heat and cooling of the heatpump and also be able to maintain the desired temps using the chilled coil. This should result in a lot less use of the heat pump and a significant saving in electrical use. I would be able to use the fan that comes with the heat pump to continually recirculate the air across the coil. To switch from cold to heat I can install selenoid valves operated by a wall mount thermostat to switch from hot water to cold water, or simply cut the pump off completely.

Does this sound like it will work?

 

[muddstopper]

I just skimmed through most of these posts but I didn't see the key answer to the problem of using 60° water to cool a house. That answer is volume. If you think about it for heating with fire like we are all familiar with, you have a small firebox, say 4 cubic feet, and are heating 10,000 cubic feet. But because the firebox is 500° it can pull the 40° difference between freezing outside up to 70-80° inside. But you are talking about a 470° temperature difference.
On the cooling side if you are using the same math, in order to use 60° water to cool in 90° weather, you would need 10,000 cubic feet of water to reach 75°. Of course good insulation will help, but you still need way more heat exchange that your typical A/C coils that run close to 35°.
Have you thought about using long loops of pipes in the floor like some use for radiant heat with a boiler.

Sent from my XT1254 using Tapatalk

I think I touched on that a little in my previous post. With a fire or airconditioner, we are looking for instant heat or cold. The faster we can get the heat of the fire or cold of the air conditioner into a house, the faster that heat or cold has to be exchanged. With the chill coil design, I think the goal is more along the lines of just maintaining the temp of the air being circulated. With building a new house,insulation will do more toward saving electricty and keeping a house warm or cold than all the gizmos we could use to get the house to the temp we desire. I like my house around 72* year round. Altho my wife will drop the thermostat to 71* in the summer and 73* in the winter. Once the house gets in those temperature ranges, the alternative heating cooling system only has to make up the difference in the amount of heating and cooling loss thru the walls, ceiling, windows and doors, not the temp outside. With that in mind, we are only talking about changeing air temps by one or two degrees, not the 20degree difference between inside and outside air. As I said, I think this type of alternate heating and cooling would be very slow in cooling a hot house or heating a cold house, but once the house is at the desired temp, then this type system should be able to maintain a stable temp. Tieing this type of alternate heating and cooling into a more conventional HVAC system should allow one to heat or cool a house as fast as the conventional system would allow and reduce the amount of electricity it would take to maintain a comfortable inside temp. I made the statement that and ideal system would change 60* water in to 80* water out and 80* air in to 60* air out. To do this it would take a lot more tubing as you are suggesting, than is found in any type of heat exchanger. Heat pumps and furnaces use extreme temps to change the temps inside a house. They cut on and blast hot or cold air into a room and then cut back off until the temps change enough to trigger the cycle to repeat. With a chilled tube. you would have a constant flow of moderately heated or cooled air.