Combined domestic hot water and house heating system

[Ronmar]

Lot of potential health issues with earth tube cooling as Bruce mentioned.  If I was going to earth cool, I think i would do it like the geothermal heat pump systems do.  Pipes buried and circulate water thru them.  Use a air to water heat exchanger(radiator) to transfer the dwelling heat into the water and ultimately into the ground.  Then you only have one condensation point to worry about maintaining cleanliness on, just like with conventional A/C...

My .02

[BruceM]

Water and fan as Ron suggests wouldn't work for my location as the water temperature would be too warm (68F+). I do think Ron's approach is a good one and it's a lot safer than earth tubes.  It all depends on your soil temperature.  

Another cooling scheme for the right climate is using  in-floor pex for a cooling heat absorber.  (Assuming you're using it for heat already- as you should!)

This won't work in a humid climate, as dehumidification is needed, and you'd have wet floors.

The water temperature can be only a few degrees below the desired room temperature with this method.  Earth source is possible in some areas.  Since I'm in high desert, where it's almost always cool and dry at night, I was planning to use a night time water cooling tower (big bong cooler), and just run the cooler and in-floor circ pump at night to chill out the house. With mid 60's outside temps that would give me 50F water for ch-ch-chilling. Only a few hours of run time at night would be needed. (House is super insulated, can hold the cool through the hot part of the day.)

By doing double wall construction, R38 sidewalls, R80 ceiling, and other design features to increase interior thermal mass and improve thermal performance, it ends up that I won't need cooling at all. I can get away with less air exchange during hot summer days because of special interior finish/material selection. (No carpets, no latex paint, no synthetic materials even in furniture, no particleboard or plywood, etc.)

[mbryner]

All good points.

I'm putting the perforated drain pipe under the foundation anyway.   Why not just have them elbow up into the basement?   If there are problems with condensation, I'll just cap them in the basement.   BruceM, what kind of climate did your friend live in?  The friend who tried earth tubes with poor results?   

Here in Southern Oregon the humidity is quite low in summer.   The HVAC guy thinks it will work great in our climate because I'll be taking maybe 30% humidity warm air and cooling it to 50%(?)-60%(?) humidity, without much condensation on the pipes.   Hope he's right...   At least he's not trying to sell me a heat pump or some other kind of energy ludicrous A/C system for my off grid house.   And since they are perforated pipe on a 2% downhill slope away from the house, any condensation *should* drain away or flow into the ground.  It won't be like the southeast where you would be taking 90% humidity air and trying to cool it underground, resulting in wet moldy drywall.    I think it will have some benefit in our area to increase the humidity, for both wood and humans.

Ronmar, your method is good, but then there's one more pump and controller.   With earth tubes, one can open an upstairs window and (hopefully) create a chimney effect to cool the house passively.


edit: spelling and readability

[mbryner]

also:

Another cooling scheme for the right climate is using  in-floor pex for a cooling heat absorber.  (Assuming you're using it for heat already- as you should!)

It would be wonderful to put in a radiant floor w/ PEX in a thin concrete pour, but there are budget constraints and I have to pick between the masonry stove (see www.heatkit.com) or radiant, and we'd rather have the masonry heater.   The rock mass of the masonry heater will help cool the house in summer, as long as the sun doesn't shine on it, which it won't because of the window overhangs upstairs and wrap around porch downstairs.   

Marcus

[Lloyd]

Hay Marcus,

I would think twice about the cooling tubes, if you think about it the tubes proposed are drains and thereby intended to have moisture, so that will raise the humidity of the house. One of the principle of a heat pump is that it also dehumidifies, thereby taking less energy to make the occupants more comfortable even at higher ambient temperatures, in summer, and lower ambient temps in winter.

It sounds to me that a water pipe exchanger cooling system would be smart. It's unlikely that you will be using that giant storage tank under the basement for heat during the summer time. So that can become your cold sink, then run a pump cycle at night time much like the ancient Egyptians did, and allow the heavens to provide the cooling. This will require a roof mounted cooling matrix.

Liang has some great 12 or 24 volt circ pumps, the pumps are designe to run off an PV & mmpt or bat bank, they draw low amperage, and are rated for 50,000 hours up to 212 degrees.

Passive design can also reduce both heating and cooling costs, so they are great. I designed and built a Solar Envelope house in the NW back in the early 80's. It was the first house that the county ever permitted that didn't require a mechanical heat source. We had to do a complete energy audit before they would issue the permit. The insulated basement was the cold/heat sink, it wasn't for habitation, there in lived a basement full of 4 man basalt rock.

We had to add mechanical dampeners to close of the envelope on the North side of the house connected to fire and smoke alarms. Because this was  a super insulated house, that was very much air tight, we had to add an air to air heat exchanger that also had a built in dehumidifier. This kept the air in the house and the basement dry, and fresh. In the summer the Solar Chimney design drew the cool air from the rock storage through the house, and in the winter the warm air was created and stored in the rocks, by the same design, just by closing the vents to the heavens.

just a thought.

Lloyd

[Ronmar]

He probably did.  I know from experience that 100f at 20% humidity is way more comfortable than 100f at 80% humidity...

[cgwymp]

I'm putting the perforated drain pipe under the foundation anyway.   Why not just have them elbow up into the basement?

Any radon problems in your area?

[mobile_bob]

the only part of the statement i would disagree with is

in winter it is beneficial to have higher humidity because it will make you feel warmer
at a lower thermostat setting.

bob g

[mbryner]

As a radiologist, you would think I would know about radon, but it's an entirely different thing, so here's a reference.   According to this website, http://oregon.gov/DHS/ph/rps/radon/county.shtml , average radon levels for Josephine Co. are 1 pCi/L.  That's about 4x lower than the recommended max in a living area.

I'm talking about taking in really low humidity air through dry gravel under a slab.   Do you guys really think it will cause that much condensation?   (I'm asking for advice not criticizing.)

re: the giant storage tank as cooling: yes, possible, but then where would I put the heated water from solar panels?   Maybe I need 2 giant tanks, 1 for hot and 1 for cold?   

[Lloyd]

One of the principle of a heat pump is that it also dehumidifies, thereby taking less energy to make the occupants more comfortable even at higher ambient temperatures, in summer, and lower ambient temps in winter.

Ummmm .... I am sure you didn't mean to say what you said ??

I did mean what I said, just for the record. If you ever lived in the south, you'll remember running the air condition in your car, even when it's in the mid 70's, because of humidity. A house with a heat pump kept at 78 degrees is very livable, and your elec. bill will be less, than if you try to keep in the low to mid 70's.

In winter an easy experiment is set your thermostat to 68, then pull a shirt from the dryer that is about 90% dry, after cools try wearing it around the house, you'll soon learn that you are more comfortable in a completely dry shirt.

Marcus, I seriously doubt there will be any benefit to making all that hot water and storing it under your house for the summer, you can easily heat the water you need for domestic use and store that in a large conventional hw tank, just ad a summer valve. As a matter of fact you could add a hot water heat pump, get a heat bump to the water, dehumidifier bump, along with some cooling bump. I use to sell the E-Tech units, for res, and apartments. They were a great investment, which lowered energy cost from the gird, and made life more comfy. They were at that time one of the best return on investment, even comparing with conservation

In the early 80's I was quiet involved in the solar movement, but the market quickly flattened when the crisis was gone.

Lloyd

[BruceM]

No way I would bring air into the house through rock or gravel.  Virtually very system that has done this has always resulted in health hazardous mold.  Even systems with just plastic tubes (like former work friend's Mesa home) have become dangerously moldy.  Good luck to the family that lives there, especially the wife and young children who spend more time in the home and may have a less robust or developing immune system.  

Even if the rock/gravel system is very dry, there are plenty of molds that don't need much moisture.  When I made some modifications to the down ducts in my existing solar hot air system, I found that while bone dry, the mold levels in the rock storage were very high.  Fortunately that air isn't brought into the home, it is just recirculated.  

As for condensation-  you have to find out weather data for your location, to find the typical humidity levels during the months and time of day of operation, and compare to the temperature of the soil at the depth of your proposed air tubes and dew point.  20% humidity is plenty of water, if dew point temperatures exist at the tube walls.  My friends house was in Mesa, AZ, with much lower humidity during periods of operation.  (He did not operate it during the monsoons.)  

I'll have to go take a look at some climate data for your county. 

I don't see running a heat pump for heating water as something I'd want to do for an off grid home; the impact on the power/battery bank/PV system size and cost is too great.  The battery bank is a significant ongoing operating expense.  Solar with propane backup seems more appropriate for most locations.

[Lloyd]

I don't see running a heat pump for heating water as something I'd want to do for an off grid home; the impact on the power/battery bank/PV system size and cost is too great.  The battery bank is a significant ongoing operating expense.  Solar with propane backup seems more appropriate for most locations.

Hi Bruce,

A properly sized unit combined with a solar water heater is going to be very efficient, and will not be a big load on the system, as it will be 1st supplemental...the amp draw is going to be on the magnitude of a small under counter refer, when it's running.

It could even be built with the new rolling piston design compressor, run on bat voltage or off a PV/mmpt.

Lloyd

Lloyd

[BruceM]

I guess it depends on your perspective on the size of your off grid power/PV systems.  Here most people view their (high efficiency) electric refrigerator as a major load for their electrical systems. There are a couple folks systems that are so big they would laugh at such a load as insignificant.

A heat pump for hot water heating is a relatively expensive system;  I  don't see the value as a backup system to solar hot water, but I'm sure there's situations where it might be great as a primary system such as in a climate where solar isn't viable.

My backup propane hot water heater requires no electricity at all, and cost $350 at the local ACE hardware store. No trouble finding a local guy to service or replace it, should I get too incapacitated for that myself.

 

[mbryner]

Heat pump for AC is out of the question.   Until we had to dig deeper for the foundataion.  I wasn't going to even have AC, because it cools down enough at night in summer to open the windows, and the thermal mass of the masonry heater should temporize temperature swings inside in the daytime.

Have to remember, our house is 2600 sq ft, w/ ~3000 watts of solar panels.   Every little load counts.   Every circulator pump, etc.   The fridge will be the major load as Bruce says.

[Ronmar]

If these tubes have perforations in them to collect drainage water and remove it from under the slab, I don't think it is a very good idea to use them for cooling.  Being from southern oregon, you have probably been in a lava cave/tube?  If the tubes you are burying have holes in them and are exposed to earth, the air that comes out of the tubes is going to smell like that which you find in a cave or in a house crawlspace...

Pumping air(you mentioned low wattage fan) and pumping air both cost energy...