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Posted by Paul M. Eldridge on May 11, 2008, 6:42 pm
wrote:
>> >Ground source heat pumps take care of that problem for the most part.
>>
>> Hi Pete,
>>
>> That may be so, but when you compare the economic performance of a
>> high-efficiency air source heat pump to that of its geo-based
>> brethren, the former prevails nine times out of ten and ten times out
>> of ten if you apply the difference in their respective cost towards
>> measures that further reduce the home's space conditioning and DHW
>> requirements.
>>
>> Admittedly, that's a pretty bold claim but I've run hundreds of
>> different scenarios using various heat loss factors, weather data,
>> utility charges, install costs, discount rates, etc. and in my
>> experience you have to push the assumptions to the far extremes before
>> you can reverse the results. That said, I'm more than willing to be
>> proven wrong if someone can provide me with hard data and I certainly
>> wouldn't object to sharing mine.
>>
>> Cheers,
>> Paul
>
>Are you comparing the labor intensive old style deep hole or large
>trench array, or the newer much better and much less labor intensive
>trenched vertical coil installation?
Hi Pete,
According to the IGSHPA, vertical closed loops are typically more
expensive than their horizontal equivalents, as quoted below.
"Horizontal installations are simpler, requiring lower-cost equipment.
However, they require longer lengths of pipe due to seasonal
variations in soil temperature and moisture content. Since a
horizontal heat exchanger is laid out in trenches, a larger area is
usually required than for a vertical system. Where land is limited,
vertical installations or a compact Slinky horizontal installation can
be ideal. If regional soil conditions include extensive hard rock, a
vertical installation may be the only available choice. Vertical
installations tend to be more expensive due to the increased cost of
drilling versus trenching, but since the heat exchanger is buried
deeper than with a horizontal system, vertical systems are usually
more efficient and can get by with less total pipe."
Source: http://www.igshpa.okstate.edu/geothermal/faq.htm
Are you referring to something other than what is described above and,
if so, can you point me to some online references?
FWIW, I was told by a HVAC contractor based in Moncton, New Brunswick
that a typical 3-ton GSHP installation (new construction) runs in the
range of $25,000.00 for horizontal closed loop and $30,000.00 for
vertical (CDN). Does that more or less jive with your figures?
Cheers,
Paul
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Posted by Pete C. on May 11, 2008, 7:26 pm
"Paul M. Eldridge" wrote:
>
> wrote:
>
> >> >Ground source heat pumps take care of that problem for the most part.
> >>
> >> Hi Pete,
> >>
> >> That may be so, but when you compare the economic performance of a
> >> high-efficiency air source heat pump to that of its geo-based
> >> brethren, the former prevails nine times out of ten and ten times out
> >> of ten if you apply the difference in their respective cost towards
> >> measures that further reduce the home's space conditioning and DHW
> >> requirements.
> >>
> >> Admittedly, that's a pretty bold claim but I've run hundreds of
> >> different scenarios using various heat loss factors, weather data,
> >> utility charges, install costs, discount rates, etc. and in my
> >> experience you have to push the assumptions to the far extremes before
> >> you can reverse the results. That said, I'm more than willing to be
> >> proven wrong if someone can provide me with hard data and I certainly
> >> wouldn't object to sharing mine.
> >>
> >> Cheers,
> >> Paul
> >
> >Are you comparing the labor intensive old style deep hole or large
> >trench array, or the newer much better and much less labor intensive
> >trenched vertical coil installation?
>
> Hi Pete,
>
> According to the IGSHPA, vertical closed loops are typically more
> expensive than their horizontal equivalents, as quoted below.
>
> "Horizontal installations are simpler, requiring lower-cost equipment.
> However, they require longer lengths of pipe due to seasonal
> variations in soil temperature and moisture content. Since a
> horizontal heat exchanger is laid out in trenches, a larger area is
> usually required than for a vertical system. Where land is limited,
> vertical installations or a compact Slinky horizontal installation can
> be ideal. If regional soil conditions include extensive hard rock, a
> vertical installation may be the only available choice. Vertical
> installations tend to be more expensive due to the increased cost of
> drilling versus trenching, but since the heat exchanger is buried
> deeper than with a horizontal system, vertical systems are usually
> more efficient and can get by with less total pipe."
>
> Source: http://www.igshpa.okstate.edu/geothermal/faq.htm
>
> Are you referring to something other than what is described above and,
> if so, can you point me to some online references?
>
> FWIW, I was told by a HVAC contractor based in Moncton, New Brunswick
> that a typical 3-ton GSHP installation (new construction) runs in the
> range of $25,000.00 for horizontal closed loop and $30,000.00 for
> vertical (CDN). Does that more or less jive with your figures?
>
> Cheers,
> Paul
Yes, something quite different than the two earlier techniques. I'm not
sure of references, but for the trenched vertical coil method you cut a
fairly narrow (~6" wide) trench something around 8' deep with a big
ditch witch and then take the plastic tubing coil and stretch it out
sideways so the coils of tube overlap at modest intervals and place the
coil in the trench. You then back fill and you're done. Far less labor
intensive then drilling holes or digging a big grid of trenches to put
single tube runs in. What they found was that the soil was such a good
thermal mass that you didn't need to cover nearly as much physical area.
This newer installation method takes perhaps 2 hrs to instal vs. all
day. Otherwise, it's the same tubing and same equipment, just a lot less
installation labor.
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Posted by Paul M. Eldridge on May 11, 2008, 10:01 pm
wrote:
>Yes, something quite different than the two earlier techniques. I'm not
>sure of references, but for the trenched vertical coil method you cut a
>fairly narrow (~6" wide) trench something around 8' deep with a big
>ditch witch and then take the plastic tubing coil and stretch it out
>sideways so the coils of tube overlap at modest intervals and place the
>coil in the trench. You then back fill and you're done. Far less labor
>intensive then drilling holes or digging a big grid of trenches to put
>single tube runs in. What they found was that the soil was such a good
>thermal mass that you didn't need to cover nearly as much physical area.
>This newer installation method takes perhaps 2 hrs to instal vs. all
>day. Otherwise, it's the same tubing and same equipment, just a lot less
>installation labor.
Hi Pete,
Thanks for the clarification. I hadn't heard of this technique before
so I appreciate you taking the time to describe it to me.
From what I understand, the cost of a ground source heat pump is
typically two to three times that of a conventional air source system
so if, for argument sake, we peg the cost of our standard system at
$7.5K the equivalent GSHP would be $15K or more. Obviously, the exact
cost of either system would depend upon a host of factors, but for now
I'm going to assume the premium runs in the range of $7,500.00.
As a quick, back-of-the-envelope exercise, an average new home with a
space heating demand of 15,000 kWh/year, if equipped with an
air-source heat pump (8.5 HSPF/Zone 4) would use roughly 6,000
kWh/year. That same home heated by a GSHP (seasonal COP of 3.75)
might come in closer to 4,000 kWh/year. The difference of 2,000 kWh
at $0.12 per kWh works out to be $240.00 a year; we might reasonably
assume DHW and air conditioning savings kick in another $360.00, in
which case our combined savings total $600.00/year -- on the other
hand, an air source heat pump with a desuperheater might claw that
back to less than $400.00. Nonetheless, if we assume an incremental
savings of $600.00, the simple payback here is 12.5 years, with
various cash discount rates and utility rate assumptions moving the
exact position one or more years in either direction. If the
breakeven point, as in this example, is more than ten years, it's fair
to say your money would be better spent elsewhere; for a lot of
consumers, even a five year breakeven point is a dicey proposition.
Again, these are rough numbers and we can fine-tune them further, but
I wanted you to understand my base assumptions.
Cheers,
Paul
|
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Posted by Pete C. on May 11, 2008, 10:34 pm
"Paul M. Eldridge" wrote:
>
> wrote:
>
> >Yes, something quite different than the two earlier techniques. I'm not
> >sure of references, but for the trenched vertical coil method you cut a
> >fairly narrow (~6" wide) trench something around 8' deep with a big
> >ditch witch and then take the plastic tubing coil and stretch it out
> >sideways so the coils of tube overlap at modest intervals and place the
> >coil in the trench. You then back fill and you're done. Far less labor
> >intensive then drilling holes or digging a big grid of trenches to put
> >single tube runs in. What they found was that the soil was such a good
> >thermal mass that you didn't need to cover nearly as much physical area.
> >This newer installation method takes perhaps 2 hrs to instal vs. all
> >day. Otherwise, it's the same tubing and same equipment, just a lot less
> >installation labor.
>
> Hi Pete,
>
> Thanks for the clarification. I hadn't heard of this technique before
> so I appreciate you taking the time to describe it to me.
>
> From what I understand, the cost of a ground source heat pump is
> typically two to three times that of a conventional air source system
> so if, for argument sake, we peg the cost of our standard system at
> $7.5K the equivalent GSHP would be $15K or more. Obviously, the exact
> cost of either system would depend upon a host of factors, but for now
> I'm going to assume the premium runs in the range of $7,500.00.
>
> As a quick, back-of-the-envelope exercise, an average new home with a
> space heating demand of 15,000 kWh/year, if equipped with an
> air-source heat pump (8.5 HSPF/Zone 4) would use roughly 6,000
> kWh/year. That same home heated by a GSHP (seasonal COP of 3.75)
> might come in closer to 4,000 kWh/year. The difference of 2,000 kWh
> at $0.12 per kWh works out to be $240.00 a year; we might reasonably
> assume DHW and air conditioning savings kick in another $360.00, in
> which case our combined savings total $600.00/year -- on the other
> hand, an air source heat pump with a desuperheater might claw that
> back to less than $400.00. Nonetheless, if we assume an incremental
> savings of $600.00, the simple payback here is 12.5 years, with
> various cash discount rates and utility rate assumptions moving the
> exact position one or more years in either direction. If the
> breakeven point, as in this example, is more than ten years, it's fair
> to say your money would be better spent elsewhere; for a lot of
> consumers, even a five year breakeven point is a dicey proposition.
>
> Again, these are rough numbers and we can fine-tune them further, but
> I wanted you to understand my base assumptions.
>
> Cheers,
> Paul
Interesting. How do you figure that would work out in North Texas (north
of Dallas) where there is a lot of A/C load in 100 degree weather and a
surprising amount of heating demand in the winter as well? Another non
monetary factor to consider is the lack of an outdoor unit with a
somewhat noisy fan, and the need to clean it regularly of dirt, pollen,
leaves, etc. This is of particular interest since I expect to replace
the full HVAC here, probably next year. I also expect to be here quite a
few years longer.
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Posted by Paul M. Eldridge on May 12, 2008, 12:47 am
wrote:
>> Hi Pete,
>>
>> Thanks for the clarification. I hadn't heard of this technique before
>> so I appreciate you taking the time to describe it to me.
>>
>> From what I understand, the cost of a ground source heat pump is
>> typically two to three times that of a conventional air source system
>> so if, for argument sake, we peg the cost of our standard system at
>> $7.5K the equivalent GSHP would be $15K or more. Obviously, the exact
>> cost of either system would depend upon a host of factors, but for now
>> I'm going to assume the premium runs in the range of $7,500.00.
>>
>> As a quick, back-of-the-envelope exercise, an average new home with a
>> space heating demand of 15,000 kWh/year, if equipped with an
>> air-source heat pump (8.5 HSPF/Zone 4) would use roughly 6,000
>> kWh/year. That same home heated by a GSHP (seasonal COP of 3.75)
>> might come in closer to 4,000 kWh/year. The difference of 2,000 kWh
>> at $0.12 per kWh works out to be $240.00 a year; we might reasonably
>> assume DHW and air conditioning savings kick in another $360.00, in
>> which case our combined savings total $600.00/year -- on the other
>> hand, an air source heat pump with a desuperheater might claw that
>> back to less than $400.00. Nonetheless, if we assume an incremental
>> savings of $600.00, the simple payback here is 12.5 years, with
>> various cash discount rates and utility rate assumptions moving the
>> exact position one or more years in either direction. If the
>> breakeven point, as in this example, is more than ten years, it's fair
>> to say your money would be better spent elsewhere; for a lot of
>> consumers, even a five year breakeven point is a dicey proposition.
>>
>> Again, these are rough numbers and we can fine-tune them further, but
>> I wanted you to understand my base assumptions.
>>
>> Cheers,
>> Paul
>
>Interesting. How do you figure that would work out in North Texas (north
>of Dallas) where there is a lot of A/C load in 100 degree weather and a
>surprising amount of heating demand in the winter as well? Another non
>monetary factor to consider is the lack of an outdoor unit with a
>somewhat noisy fan, and the need to clean it regularly of dirt, pollen,
>leaves, etc. This is of particular interest since I expect to replace
>the full HVAC here, probably next year. I also expect to be here quite a
>few years longer.
Hi Pete,
I can explore this in more detail later on when time permits, if you
so wish, but right now it's getting late and I'll soon have to call it
a night.
Anyway, in terms of operating performance, SEER ratings are suppose to
be reasonably representative of what we can be expect to encounter
over the course of the entire cooling season. However, if it is
helpful, EER is based on steady-state operation at a 95F ambient
temperature (not far from the 100F mark you mention). To get a rough
sense of how these two numbers compare, you can convert SEER to EER by
multiplying the former by either 0.9 (relatively low humidity) or 0.8
(high humidity). So, if we assume you live in a hot and humid area,
an ultra high efficiency heat pump with a 21 SEER rating would have an
EER of 16.8 and a high efficiency model with an 18 SEER rating would
have an EER of 14.4. To then convert EER to COP -- a more useful
measure when comparing these products to GSHPs -- take this second
number and divide it by 3.4. Thus, our 21 SEER unit would have a COP
in the range of 4.9 (@ 95F) and the 18 SEER version would clock in at
about 4.2. Again, this is a rough approximation, but the results seem
to be more or less in line with what we could expect from a typical
GSHP.
Your concerns related to noise are hard for me to address. The CAC in
my Toronto home is a two-stage high efficiency model and on the low
setting the outside compressor is surprisingly quiet (a light and not
unobjectionable hum). I don't ever recall it kicking on high so I
can't honestly tell you how loud it is when operating at full
capacity. I don't believe I had any issues with dirt, leaves or
pollen -- I may have washed down the outer cabinet with soap and water
once or twice but that's basically it.
A GSHP may very well prove your best choice given your particular
needs, utility costs, operating environment and so on -- I really
can't say. But I wouldn't automatically rule out a high-efficiency
air source heat pump without investigating this option further; these
products have really come a long way in recent years. Whatever you
ultimately decide, good luck!
Cheers,
Paul
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