Heat Pump In Encapsulated Crawlspace instead of outside?

DogFather

DogFather

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Odd Crazy question - my crawlspace is sealed off with a monster of a dehumidifier that runs about 10 hours a day. Remote monitor tells me the humidity is maintained at about 55% - is that about right? Should I set it lower?

Also, the main question, the temp seems to stay about 55 - 65F so it would seem more efficient to have the house heat pump pull heat from the crawl space in winter and dump heat there in summer. Or am I missing something? Currently the heat pump compressor is outside so it obviously has to work hard on cold days & hot days.

I've also thought about trying to put a heat pump water heater in the crawlspace but that will be a challenge with only 4 feet max clearance.
 
DogFather said:
Odd Crazy question - my crawlspace is sealed off with a monster of a dehumidifier that runs about 10 hours a day. Remote monitor tells me the humidity is maintained at about 55% - is that about right? Should I set it lower?

Also, the main question, the temp seems to stay about 55 - 65F so it would seem more efficient to have the house heat pump pull heat from the crawl space in winter and dump heat there in summer. Or am I missing something? Currently the heat pump compressor is outside so it obviously has to work hard on cold days & hot days.

I've also thought about trying to put a heat pump water heater in the crawlspace but that will be a challenge with only 4 feet max clearance.
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It will take about 10 minutes of running and the Temps in the crawl space will be higher than the outside Temps in the summer.

I can't think of anything more ridiculous to do with an ac system than that.
 
Taking the heat from inside the house and putting it under the house to rise back into the house and vice versa? That sounds like a null sum game.
 
The dehu discharge air is about 10 degrees warmer than the air coming in so no need to add heat in an encapsulated crawl space. Keep the house air in the house. I can't tell you how many times I've seen people put vents in their garage (not thinking about the CO their cars puts off) or in other odd spaces that aren't part of the conditioned envelope. The air in the house has supplies and returns and you want 100% of the air being supplied returned or else you will cause negative pressure which will cause infiltration of outside air and inefficient operation.
 
DogFather said:
Remote monitor tells me the humidity is maintained at about 55% - is that about right?
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Quick google says that less than 50% is ideal and 30-50% is normal. At the temperature of 55-65, it sounds like you still have a fair amount of water in the air, but as long as you're not having mold or condensation issues you're probably ok.

it would seem more efficient to have the house heat pump pull heat from the crawl space in winter and dump heat there in summer. Or am I missing something?
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Remember that any sort of heat pump / air conditioner is moving heat from one location to another. There is an electrical cost to this, as you well know. While an AC unit is often looked at in terms of EER (or SEER) which indicates how much heat is moved relative to the electrical usage, but there is still overall inefficiency in the system. What you're describing would is moving the heat from one location to a secondary to a tertiary location (house, crawlspace, outside). The heat moved to the crawlspace in the summer will won't benefit you, and unlike an aquifer or lake (some large geo-thermal systems do try to store the seasonal energy) won't act like a thermal battery, it will just end up costing you more to move the heat, twice instead of directly outside.
 
DogFather said:
OK, sounds like this might be the top dumb question of the day. Do I get the "Idiot of the day award" ?
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Maybe.

I did see a house that had dehumidifiers in the crawl space, but the crawl space had open vents to the outside.
 
cold1 said:
Maybe.

I did see a house that had dehumidifiers in the crawl space, but the crawl space had open vents to the outside.
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I had one contractor insist the best way to prevent crawlspace mold was fans to vent outside air into crawlspace & dehumidifiers.

I said no thanks how 'bout next time we talk it is over beers instead of home repairs.
 
DogFather said:
OK, sounds like this might be the top dumb question of the day. Do I get the "Idiot of the day award" ?
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Too early for the judges to decide. 😂

I too have a monster dehumidifier in the crawlspace. No idea whether it’s correct or not but I’ve got it set around 44% now.
 
If your dehumidifier is running 10 hours every day, then your crawl is not sealed.

I don’t understand why geothermal heat pumps aren’t really common in the Carolinas, we have perfect weather for them.
 
Windini said:
Are dehydrated monsters a good prepper food supply?

I mean the chewy meat kind, not the open can & add water energy drink kind.
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Not sure about anything other than that mine consumes a HUGE amount of energy.
 
JimB said:
If your dehumidifier is running 10 hours every day, then your crawl is not sealed.

I don’t understand why geothermal heat pumps aren’t really common in the Carolinas, we have perfect weather for them.
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When we were designing our home, in about 1997, we couldn’t find a contractor willing to do geothermal. I’ve always regretted that.
 
JimB said:
If your dehumidifier is running 10 hours every day, then your crawl is not sealed.

I don’t understand why geothermal heat pumps aren’t really common in the Carolinas, we have perfect weather for them.
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Cost. Plain and simple. I'm not in the HVAC business but I've hung out in the supply houses enough to know that most geothermal systems are in in houses that list for $1M and a few HVAC contractors have put them in their own homes.
 
cold1 said:
Cost. Plain and simple.
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We put one in my parents house. In terms of cost, the equipment and installation was roughly double that of a conventional heat pump. The total system: 3 ton geothermal heat pump with 3x 220' vertical wells (they're more efficient than horizontal), humidifier, de-humidifier, an ERV, rigid and sealed duct in an H-Bridge design with supply and returns in all the major areas (every bedroom and the central great room), was roughly $60,000. However, the lifespan of a geo-thermal heat pump is statistically double that of a conventional one; the equipment (except for the wells) is inside the semi-conditioned basement and nothing is exposed to wild temperature swings or outside weather. The HDPE in the wells themselves is rate estimated for about 100 years and has no moving parts.

So:
1) double the equipment cost, but double the life expectancy. Aside from the future value of money aspect, the cost is a wash

2)Efficiency: summertime AC efficiency is typically equivalent to that of a SEER 40 system as it typically only needs 1 compressor stage, otherwise it's a 20. Winter COP is 7. The pump runs 9.0 GPM and I have used an IR thermometer on the water supply and return lines and saw an 8 degree differential, which works out to exactly 3 tons.

3) We also have a de-superheater that goes to a hydronic storage tank that feeds the water heater. Excess heat from the heat pump is used to heat that water to up to 120F, which means far less energy to make hot water because you're not trying to raise it from ground temperature.

4) Very quiet. There is no compressor / condenser fan system buzzing and humming at 90 dB out in the back yard.

5) Extra money spent on IAQ and duct work means higher efficiency, year round comfort, and except for a few things in the corners, my mother says they never have to dust.

6) The range hood pulls up to 700 CFM (they have a high BTU stove). The intake air is through the ERV, so you're not pulling in hot air in the summer and cold air in the winter when you run it.

I estimate their electric bill for AC (based upon when the AC was on during construction before they moved in) to be about $65 per month.
 
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JimB said:
If your dehumidifier is running 10 hours every day, then your crawl is not sealed.

I don’t understand why geothermal heat pumps aren’t really common in the Carolinas, we have perfect weather for them.
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I used to do HVAC in Tennessee and TVA had all kinds of incentives and rebates to do geothermal - here in NC not a lot of incentives. They are probably the best and longest lasting systems you can get but a lot of folks choke on the upfront cost. Keep an eye out on VRF systems (larger multi-zone mini-split systems that also can have ducted components). They are an excellent option if you are doing a larger home and want excellent efficiency and zoning. You are probably right about his crawl not being properly sealed.
 
Jeppo said:
When we were designing our home, in about 1997, we couldn’t find a contractor willing to do geothermal. I’ve always regretted that.
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Back in 1980 SUNY Stonybrook installed three 300' wells for geothermal system for a new engineering building. I think they got some DOE grant back then.
 
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cold1 said:
Cost. Plain and simple.
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yep, pretty much. I marketed & sold a specialty thermal grout for geo systems for about 6 years and learned a lot during that time.

From memory (and at least 4 years out of date):

-Geothermal systems are the most efficient way to heat & cool a building, period.They are on the order of 400% to 500% efficient, i.e. for every KW used to power the system, it produces the equivalent of 4 to 5 KW of heating/cooling energy. ASHPs are about 200%, but improving.
-Properly designed & installed geo systems can handle 100% of a year-round heating & cooling needs, anywhere on the planet. Obviously, the size of the loop field needed may make that impractical in extreme conditions. But there is no theoretical limit to cooling or heating capacity.
-They eventually pay for themselves in cost savings, but most people & businesses move before the initial buyer recoups the extra cost.
-Tax incentives help shorten the payback period. (Guess whose Prez admin let the most energy efficient HVAC system incentives expire? Guess which one re-instated them?)
-The big difference in cost btw conventional ASHP heat pump and geo heat pump systems is almost always the thermal loop. Whether you excavate, trench, or bore, you're paying for a LOT of work and some equipment that ASHPs don't require.
-Specific to NC, NC's DENR and many local gubmints are hyper-regulated in ways that directly discourage geo systems. These regs are couched in "Groundwater / Water Protection" language that is often absurd when applied to geo systems.
 
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Installed a system in South Bend Indiana, President Carter footed a lot of the bill as I recall. Don’t remember much about it, but we had 4 bores, each 400 ft and I had to finish the trenching between them by hand, I do not know why! Had solar hot water panels, all the boiling water you’d ever want year round, took some tuning not to vapor lock the system and it never froze. Think this was 1978. Gawd, I’m like my grandparents telling stories about the depression.
 
What can be done about the perpetual rain caused by dripping duct work?
 
Windini said:
The big difference in cost btw conventional ASHP heat pump and geo heat pump systems is almost always the thermal loop. Whether you excavate, trench, or bore, you're paying for a LOT of work and some equipment that ASHPs don't require.
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We helped offset this by having the domestic water well driller do all four wells (three heat pump, one domestic) at the same time.
 
JohnFreeman said:
What can be done about the perpetual rain caused by dripping duct work?
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Insulation. If your duct work is dripping, it means it cooling below the dew point. You need to start with it DRY, but proper insulation will create a barrier where the dew point temperature is somewhere in the insulation where there is no moisture (hence no condensation). Figure that have a linear temperature gradient between the duct and the outside of the insulation. The dew point, then occurs somewhere in the middle.
 
www.thisoldhouse.com

Future House | Affordable Geothermal

Ask This Old House home technology expert Ross Trethewey travels to Albany, New York to explore ways to make drilling for and installing geothermal heat pumps more affordable for average homeowners.
www.thisoldhouse.com www.thisoldhouse.com
 
Button Pusher said:
www.thisoldhouse.com

Future House | Affordable Geothermal

Ask This Old House home technology expert Ross Trethewey travels to Albany, New York to explore ways to make drilling for and installing geothermal heat pumps more affordable for average homeowners.
www.thisoldhouse.com www.thisoldhouse.com
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Full Disclosure: I dint read this article and I dunno much about Dandelion... but:


Dandelion is a "Google- backed" geothermal company. This made me very suspicious and distrustful as soon as I heard about it a few years ago.

My gut reaction is that this company is an attempt to co-opt the geothermal market and "solarize" it, i.e. restructure the market to make it wildly profitable for a handful of well-connected govcorporamental execrueacrats. Tinfoil? Mebbe. But it's recycled aluminum! I've already used it to make a number of other hats.

IMO: One (big) reason geothermal isn't a household word the way solar or wind is is the dirty politicization game behind the energy scenes.



Note: I'm stopping here in this thread so that I don't hijack @DogFather 's thread with a rant. I may add an EDIT to this post and link it to said rant in a different thread.
 
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