How
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| 10 Apr 2010 05:41 PM |
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Wednesday, March 10, 2010
Manley Architects and Geo-Thermal Heating and Cooling
In our continuing effort to advance sustainability issues, Manley Architects recently updated HVAC systems at our home occupancy location to geo-thermal. The geo-thermal heat pump system was installed by Hendrickson HVAC of Battle Ground, Washington and engineered by Hendrickson’s own Howard Eck.
Geo thermal heat pumps operate at as much as 70% greater efficiency than conventional air to air heat pumps. Here’s how it works – simply stated. Using the stable temperatures found from 4’ and deeper below grade, a geo-thermal heat pump system circulates a refrigerant - typically water with an anti-freeze additive - through pipes in the ground known as the “ground loop”. The refrigerant absorbs or sheds heat through contact of the piping with the earth. The heat pump compressor unit then borrows the ground's heat (or sheds heat from the home if in cooling mode) much like a typical air to air heat pump, but using the earth’s stable temperature instead of outside air to heat or cool. The department of Energy has a decent primer on the basics (Dept of Energy Geo Thermal). Our system includes a 3 ton, 2 stage variable speed Climate Master heat pump, served by 2,400 linear feet of horizontal ground loop. A “de-super-heater” system uses waste heat from the home heating system to heat domestic hot water for further energy savings.
Given our small, built-out existing urban site and it’s distinctly Columbia River Valley soils sub-strates, our project created some real challenges and called for true creativity in engineering.
Optimally on a small footprint site, ground loops for refrigerant water will be “vertical”, grouted into cased wells drilled into the earth from vertical to about a 20 degree angle from vertical. A notable example of a geo-thermal heat pump installation on a small urban site is the design for the “Red Steps” building housing a TKTS outlet at Father Duffy Square, Times Square New York (Green Buildings New York). The TKTS booth, which is housed in an enclosure beneath the red steps, is conditioned by a geo thermal heat pump system served by wells. Our new system originally called for three 250’ deep wells. Our driller encountered cobble at a depth of about 20’. The material encountered is typical of gradated river rock deposited by the Missoula Floods during the last ice age. With its round “bowling ball” shape, the drill bit bounced off the cobble like a pinball in an arcade; entertaining, but unproductive! Drill rigs capable of handling the cobble were not available before the next heating season; it was time for plan B.
For us, plan B was making a horizontal ground loop on a small site pan-out. To make this happen, Hendrickson HVAC used a slinky coil arrangement for the ground loop piping and embedded the coils in pervious concrete at a depth of 4’. The higher rating for thermal conductivity of the pervious concrete increased the exchange of heat versus direct contact with soil just enough to make the system viable.
Our system has been up and running since the end of October 2009. In that time we’ve seen our natural gas usage (water heating and other uses) cut by more than 50%. We’re still evaluating our electricity savings as weatherization of the existing structure continues, but the savings in electric utilities also appear significant.
Along with the energy savings, our local public utility, Clark PUD, offers a $2,000 rebate for installation of a geothermal heat pump. This is typical of programs offered by utility vendors nationwide. This when combined with existing federal tax credits and further incentives and tax credits recently proposed by the Obama administration make upgrades for energy savings and greater sustainability a choice everyone should consider. |
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robinnc
Basic Member
Posts:216
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| 10 Apr 2010 10:45 PM |
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pervious
concrete...that's very interesting! Never heard of that before. How deep do the coils have to be in the concrete....2" below and 2" above?....How much does that type of concrete cost/yrd?
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How
New Member
Posts:44
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| 12 Apr 2010 09:28 AM |
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We put 6", 3" below and 3" above. ~$90/yard. |
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joe.ami
Veteran Member
Posts:2004
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| 12 Apr 2010 07:50 PM |
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" The higher rating for thermal conductivity of the pervious concrete increased the exchange of heat versus direct contact with soil just enough to make the system viable."
We have discussed ways of extracting more heat from less area and keep returning to the same thing; the soil is the limiting factor.
I'm having a hard time trying to wrap my head around how concrete, pervious or otherwise, poured around loops can extract more heat out of the ground. Afterall if the termal conductivity of the adjacent soil is poor, how do you benefit from extracting btu's from the ground more quickly than it can replenish them?
Joe |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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How
New Member
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| 12 Apr 2010 08:13 PM |
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The concrete "bridge" did the trick. |
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joe.ami
Veteran Member
Posts:2004
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| 12 Apr 2010 08:21 PM |
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Posted By How on 12 Apr 2010 08:13 PM
The concrete "bridge" did the trick. Bridge suggests something linked to something else......are you suggesting that you bridged to superior soil? I'm not trying to nit pik, I'm trying to understand. Joe |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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How
New Member
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| 14 Apr 2010 06:31 PM |
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The "bridge effect" was the exact same dirt. |
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engineer
Veteran Member
Posts:1734
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| 14 Apr 2010 11:11 PM |
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Maybe not superior soil, but perhaps more soil. Concrete seems to me here to act like grout, an intermediate material between pipes and soil.
Pervious concrete introduces an interesting variable. I assume that pervious concrete refers to an ability to diffuse / disperse far more water than is usual for concrete; all the rage in green driveways as it purports to manage some rainfall by carrying it into the ground rather than sluicing it away adding to surface runoff.
Pervious concrete surrounding geo lines would seem to me to add considerable heat transfer when wet since significant water enters the concrete. OTOH if pervious concrete dries out, I'm guessing that heat transfer would plummet owing to dry voids acting as insulators. Heaven help a system so configured during a hot drought period.
Just my $0.02, not backed by data or experience. |
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Curt Kinder
Absent data, you have only an opinion.
No thing done well is as simple as it seems
www.hoviscustombuilders.com
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joe.ami
Veteran Member
Posts:2004
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| 16 Apr 2010 09:45 AM |
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Posted By How on 14 Apr 2010 06:31 PM
The "bridge effect" was the exact same dirt. Ok, your brevity suggests impatience with an unwashed layperson like myself, but does little to explain the benefit to your loop system. Engineer took a shot at it, but here's the thing, if you could come into contact with enough soil with your loops encased in concrete, you could come into contact with enough soil without concrete. That it is pervious and permits greater water flow, only works when water flows. Flowing water of course improves performance of any loop field. You are suggesting that concrete moves heat better than surrounding soil, but you are not suggesting how it gets surrounding soil to deliver heat more quickly since concrete is present. What you did was improve the size of your loop system without increasing loop size and dropped it in a footprint that was less than design standards. Since most standards have fudge factor, you may get away with it, but if you do I'm suggesting you could have done it without the concrete by simply adding loops in a condensed pattern (cheaper). j |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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How
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engineer
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| 18 Apr 2010 09:36 AM |
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That site seems to advocate storing heat in a big block of pervious concrete placed underground and sealed so as to always be wet. How that would be better than a simple tank of water placed underground is not clear to me. Water has higher specific heat than concrete and is generally cheaper. Furthermore, the issue germane to a geo loop is moving heat, not storing it.
Merely surrounding slinkies with pervious concrete incorporates no provision for continuous saturation with water, infact I would expect it to drain and dry fairly quickly if water table drops. Therefore I continue to share Joe's skepticism with the efficacy of pervious concrete.
Since this is a horizontal loop I expect it could easily dry out during dry weather, and that the dry pervious concrete's conductivity would then drop precipitously, possibly resembling that of dry sand or gravel, soil types requiring much more loop footage per ton than others.
Please do keep us updated as summer comes and goes, especially if a period of dry weather ensues.
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Curt Kinder
Absent data, you have only an opinion.
No thing done well is as simple as it seems
www.hoviscustombuilders.com
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geodean
Veteran Member
Posts:1264
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| 18 Apr 2010 09:48 AM |
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I am skeptical as well. |
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Dewayne Dean
Do not argue with an idiot. He will drag you down to his level and beat you with experience.
www.PalaceGeothermal.com
Why settle for 90% when you can have 400%
We heat and cool with dirt!
visit- http://welserver.com/WEL0114/- to see my system |
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Looby
Basic Member
Posts:134
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| 18 Apr 2010 02:55 PM |
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Posted By engineer on 18 Apr 2010 09:36 AM
How that would be better than a simple tank of water placed underground is not clear to me.
As I understand the explanation on their web site, pervious concrete is
a trade-off between BTU storage capacity and storage/retrieval rate.
Pervious concrete is a much better thermal conductor than water, and
(they claim) that allows them to store/retrieve BTUs more quickly than
would be possible with a big tank of standing water. That argument
makes sense to me -- think of the pervious concrete as a substitute
for a large mechanical stirring paddle inside the tank.
OTOH, I don't see how that logic has anything to do with a geo loop field.
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| One measurement is worth a thousand expert opinions. |
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joe.ami
Veteran Member
Posts:2004
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| 19 Apr 2010 09:20 AM |
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Posted By Looby on 18 Apr 2010 02:55 PM
OTOH, I don't see how that logic has anything to do with a geo loop field.
Nor I. I did recieve a PM from OP who cites a medical condition that makes typing difficult explaining brevity of answers and use of links and what look like press releases vs conversational blogging. I hope How understands that the occasional carpet bagger will try to advertise a new system here, inflate their expertise or present a wild @$s theory as a system in use. That said we will always be especially inquisitive of something new who's value escapes us. j |
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Just a Mechanic;
Geothermal; Savings Underfoot |
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How
New Member
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| 19 Apr 2010 04:37 PM |
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Was it worth including on the blog? Yes  or no  ? |
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joe.ami
Veteran Member
Posts:2004
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| 20 Apr 2010 09:16 AM |
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Contrary to what some may think, I'm not opposed to new ideas. If their is a way that you can communicate actual system to us.....soil conditions, system tonnage, loop design and length, manual j load......and actual usage; then we could determine whether a breakthrough has been made or not.
We've no reason to take it for granted the concrete was worth the extra effort or expense, but hope your system works well for you.
Good Luck,
Joe
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Just a Mechanic;
Geothermal; Savings Underfoot |
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How
New Member
Posts:44
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| 22 Apr 2010 11:13 AM |
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What makes the pervious concrete so special? Let's say you had a slinky loop with native fill around it. Contact area: 3.14 cubic inches per 3/4 inch geopipe.
Pervious concrete added: Contact area: >>>>greater!
I live a spot where it rains and rains and rains!!! There is not much need for air conditioning. |
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geome
Advanced Member
Posts:556
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| 22 Apr 2010 11:33 AM |
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Wouldn't pervious concrete saturated with water have problems if loop temperatures drop below 32f? |
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| WF Envision NDV038 (packaged) & NDZ026 (split), one 3000' 4 pipe closed horizontal ground loop, Prestige thermostats, desuperheaters, 85 gal. Marathon. |
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How
New Member
Posts:44
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| 22 Apr 2010 12:08 PM |
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No. It is used mostly for sidewalks. |
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Looby
Basic Member
Posts:134
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| 22 Apr 2010 12:16 PM |
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Posted By How on 22 Apr 2010 11:13 AM
... Contact area: 3.14 cubic inches per 3/4 inch geopipe. ...
Could you please explain what that means?
My lame (non HVAC pro) engineering brain can't grok a
"contact area" stated as: "cubic inches per 3/4 inch."
Also don't understand how pervious concrete would be
fundamentally different than native backfill materials
(e.g., coarse sand/gravel) in terms of "contact area."
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| One measurement is worth a thousand expert opinions. |
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