Posted by daestrom on July 26, 2008, 12:56 pm
Neon John wrote:
>> Even if all they did was circulate warm condenser cooling water to
>> the city to be used as the heat source for water-source heat pumps,
>> one still has to figure out how to pay for the plumbing. It surely
>> would not compete with simple ground-sourced heat pumps on an
>> economic basis.
>>
> I wrote the above as it popped into my head during a previous post.
> I've given it a couple hours' thought and I see some possibilities.
> A large power plant has a condenser cooling water flow rate measured
> in the millions of gallons per minute. The temperature rise through
> the condensers is in the 5 to 15 deg range, typically. Lots of
> slightly warmed water. The water is not hot enough to be useful for
> comfort heating but it DOES contain lots of low quality energy. A
> heat pump is a device that takes low quality heat and turns it back
> into higher quality heat. An idea is born.
> Suppose that a portion of or all of this water were diverted into
> canals, open or closed topped, that carry the warmed water to a
> nearby town. Homes and businesses along the canals could pump the
> water to water-sourced heat pumps. Or an alternative would be to put
> the refrigerant coil directly in the water if the house isn't too far
> away.
Well let's see. I use about 80 MMBTU to heat my house over a typical winter
of four months (200 Therm/month). That works out to about 28 kBTU/hr. If
about half of the waste heat is lost along the way, a 1000 MWe plant with
about 2000 MWth discharge would have 1000 MWth for customers. So that
plant could heat over 120,000 homes if the plumbing could be made to fit.
Now, I pay about $1.25 / Therm for NG so that works out to about $250 /
month in winter. If a heat pump runs at COP of 3 with this water, it would
take about 1950 kW-hr a month to get the same 200 Therms and that would cost
me about $253 / month ($0.13/kWh). So that leaves nothing to 'pay' for the
use of the water. Nor the cost of my heat pump upgrade.
OTOH, if the plant could supply me with water at 120 degF, I wouldn't need a
heat pump at all (saves me capital costs and some maintenance), I could pay
the full $250/month that I currently pay for NG. (and of course my NG costs
are expected to rise in the coming years)
If the plant can find users for only 25% of the waste heat (1/2 gets 'lost'
in distribution and only 1/2 of the rest can be delivered to paying
customers), that would be about 60,000 homes @ $250 / month. That comes out
to $15M a month or an average of $20,833 / hr. At today's prices for
electric (~$50/MWhr off-peak), that's equivalent to about 416 MW electric
production for the plant.
So the bottom line is that if the plant were designed to run with hotter
circ-water temperatures and can get the water to the customers (I don't
think open canals would work for hotter water, too much loss), it could be
quite a revenue stream. (pun intended ;-). Such a plant might sacrifice 200
MW of electric production revenue in exchange for more than 400 MW in
thermal supply revenue.
daestrom
Posted by Neon John on July 26, 2008, 4:40 pm
On Sat, 26 Jul 2008 12:56:27 -0400, "daestrom"
>Well let's see. I use about 80 MMBTU to heat my house over a typical winter
>of four months (200 Therm/month). That works out to about 28 kBTU/hr. If
>about half of the waste heat is lost along the way, a 1000 MWe plant with
>about 2000 MWth discharge would have 1000 MWth for customers. So that
>plant could heat over 120,000 homes if the plumbing could be made to fit.
Where do you live and what kind of home do you have? That's about twice the
therms of what it takes to heat my mom's 2500 sq ft ranch with 70's era
insulation.
>Now, I pay about $1.25 / Therm for NG so that works out to about $250 /
>month in winter. If a heat pump runs at COP of 3 with this water, it would
>take about 1950 kW-hr a month to get the same 200 Therms and that would cost
>me about $253 / month ($0.13/kWh). So that leaves nothing to 'pay' for the
>use of the water. Nor the cost of my heat pump upgrade.
Actually the advantage to the heat pump is much better than that. First, the
COP of water sourced heat pumps is significantly better than 3. I didn't know
numbers off the top of my head so I went googling. First significant hit:
http://www.oee.nrcan.gc.ca/regulations/product/ground-water-heat-pumps.cfm?Text=N&PrintView=N
These are minimum requirements and are based on 50 deg water. Let's be
conservative and call a typical COPh 4.0.
Next, you must pay attention to the definition of COP. That page above words
is well.
"... [COP is] calculated by dividing the [heat pumping] capacity expressed in
watts by the power input in watts, excluding any supplementary heat".
If an AC pumps 3000 watts of heat out of the house using 1000 watts of
electricity then the COPc is 3. But with heating that's not the whole
picture. With the AC, the total heat rejected to the heat sink (air or water)
by the condenser is the SUM of the watts. 3000 watts from inside the house
PLUS the 1000 watts consumed by the compressor. The electrical energy,
ultimately dissipated as heat, is wasted.
Quite the opposite is true in the case of COPh. When heating with a heat
pump, 3000 watts is extracted from the outside heat source (air or water) and
pumped into the house, transferred to the air flowing through the indoors
condenser coil. Another 1000 watts of electrical energy consumed by the
compressor is also transferred to the air by the condenser. A total of 4000
watts is discharged to the warm air duct.
If the water source heat pump has a COPh of 4.0, then the ratio of heat
provided by the system to the power consumed is COPh + 1 or 5X the electrical
power consumption.
If a COP 4 heat pump draws 1000 watts of electrical energy then it delivers
FIVE thousand watts of heat. 4000 watts from the refrigeration cycle and 1000
watts from the electrical supply.
If you re-figure the case using these numbers then the heat pump option looks
much better. The heat pump looks even better when electric rates are lower
than yours (mine is a click under 8 cents) and gas is higher. (Chattanooga Gas
http://www.chattanoogagas.com/Universal/RatesandTariff.aspx lists the first 25
therms at $1.3444/therm plus a $12/month "meter fee" as of this instant. Being
summer, the fuel adjustment is slightly negative so the price per therm will
be significantly higher in winter.)
For folks heating with propane or oil, this would be a dream come true. I was
just quoted $2.79/gallon for propane if I pay for the winter's supply now.
Looks like I'll be skipping propane heat again this year. I'm lucky to have
that option.
Another consideration is that if water-sourced heat pumps were manufactured in
similar volumes to air sourced pumps then the cost based on materials used
should be significantly less. A small water/refrigerant heat exchanger
contains MUCH less copper and aluminum than a high EER air coil. Plus the
relatively large condenser fan motor and fan is eliminated. Depending on
geography, a small water circulating pump might be necessary but the motor and
pump are smaller and consume less power.
>OTOH, if the plant could supply me with water at 120 degF, I wouldn't need a
>heat pump at all (saves me capital costs and some maintenance), I could pay
>the full $250/month that I currently pay for NG. (and of course my NG costs
>are expected to rise in the coming years)
I think that 120 deg water would require augmenting. 120 deg low humidity air
is cold-feeling, as many an early heat pump user learned. Even the 140-150
deg air from my heat pump is at best, neutral feeling, neither particularly
hot nor particularly cold. The reason air that hot doesn't feel warm is
because the RH is near zero. My cabin typically runs 20% humidity in the
winter at 70 deg. When air that dry is heated, the humidity drops to near
zero, lower than my HVAC temperature/humidity instrument can measure.
Under-floor radiant heat might work with that cool a water supply. The
radiant systems I have experience with usually run closer to 180 deg. It
would probably take special construction that put the water tubing right at
the surface of the floor.
Still, 120 deg water would be an excellent source of heat for a heat pump. A
COPh of 5 or more would probably be possible.
>If the plant can find users for only 25% of the waste heat (1/2 gets 'lost'
>in distribution and only 1/2 of the rest can be delivered to paying
>customers), that would be about 60,000 homes @ $250 / month. That comes out
>to $15M a month or an average of $20,833 / hr. At today's prices for
>electric (~$50/MWhr off-peak), that's equivalent to about 416 MW electric
>production for the plant.
>So the bottom line is that if the plant were designed to run with hotter
>circ-water temperatures and can get the water to the customers (I don't
>think open canals would work for hotter water, too much loss), it could be
>quite a revenue stream. (pun intended ;-). Such a plant might sacrifice 200
>MW of electric production revenue in exchange for more than 400 MW in
>thermal supply revenue.
I tend to agree. It would be interesting for someone to do a case study of a
specific plant to see how the finances work out. Maybe someone could pick up
on this and do a master's thesis....
John
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN
No one can be right all of the time but I'm getting close.
Posted by daestrom on July 28, 2008, 8:00 pm
Neon John wrote:
> On Sat, 26 Jul 2008 12:56:27 -0400, "daestrom"
>> Well let's see. I use about 80 MMBTU to heat my house over a
>> typical winter of four months (200 Therm/month). That works out to
>> about 28 kBTU/hr. If about half of the waste heat is lost along the
>> way, a 1000 MWe plant with about 2000 MWth discharge would have 1000
>> MWth for customers. So that plant could heat over 120,000 homes
>> if the plumbing could be made to fit.
> Where do you live and what kind of home do you have? That's about
> twice the therms of what it takes to heat my mom's 2500 sq ft ranch
> with 70's era insulation.
A nice 2600 sq ft colonial in upstate NY (built in 2000). We average about
4 months below freezing and thaw out in mid March. Not much different than
several metro areas, Buffalo, Detroit, Chicago.
200 Therm's a month is considered quite good for an area that runs about
1100 degree-days a month from mid-November to mid-March.
>>
>> Now, I pay about $1.25 / Therm for NG so that works out to about
>> $250 / month in winter. If a heat pump runs at COP of 3 with this
>> water, it would take about 1950 kW-hr a month to get the same 200
>> Therms and that would cost me about $253 / month ($0.13/kWh). So
>> that leaves nothing to 'pay' for the use of the water. Nor the cost
>> of my heat pump upgrade.
> Actually the advantage to the heat pump is much better than that.
> First, the COP of water sourced heat pumps is significantly better
> than 3. I didn't know numbers off the top of my head so I went
> googling. First significant hit:
>
http://www.oee.nrcan.gc.ca/regulations/product/ground-water-heat-pumps.cfm?Text=N&PrintView=N
> These are minimum requirements and are based on 50 deg water. Let's
> be conservative and call a typical COPh 4.0.
If their number for 10C (50F) is 3.6 and 3.1 for 0C (32F), how does 4.0 come
out 'conservative'?? Seems a number like 3.4 or so would be more
'conservative'. You *did* mention supplying it with 50F water in your
original post. To get up to 4.0 you'd have to supply it with something
warmer than 50F.
> Next, you must pay attention to the definition of COP. That page
> above words is well.
> "... [COP is] calculated by dividing the [heat pumping] capacity
> expressed in watts by the power input in watts, excluding any
> supplementary heat".
Ah, no. You added the '[heat pumping]' qualifier, that's not the definition
of the unit's 'capacity'. The 'capacity' of the unit in the heating mode is
the heat *delivered* to the house, not the heat pumped nor the heat 'sucked
in' from outside. As such, this capacity includes the energy for running
the compressor.
So your rambling below is wrong.
> If an AC pumps 3000 watts of heat out of the house using 1000 watts of
> electricity then the COPc is 3. But with heating that's not the whole
> picture. With the AC, the total heat rejected to the heat sink (air
> or water) by the condenser is the SUM of the watts. 3000 watts from
> inside the house PLUS the 1000 watts consumed by the compressor. The
> electrical energy, ultimately dissipated as heat, is wasted.
> Quite the opposite is true in the case of COPh. When heating with a
> heat pump, 3000 watts is extracted from the outside heat source (air
> or water) and pumped into the house, transferred to the air flowing
> through the indoors condenser coil. Another 1000 watts of electrical
> energy consumed by the compressor is also transferred to the air by
> the condenser. A total of 4000 watts is discharged to the warm air
> duct.
> If the water source heat pump has a COPh of 4.0, then the ratio of
> heat provided by the system to the power consumed is COPh + 1 or 5X
> the electrical power consumption.
> If a COP 4 heat pump draws 1000 watts of electrical energy then it
> delivers FIVE thousand watts of heat. 4000 watts from the
> refrigeration cycle and 1000 watts from the electrical supply.
Here in the US, a heat pump's COP is defined as the total heat into/outof
the living space divided by the electrical energy input. That is why there
is a difference between cooling and heating. It already considers the
'waste heat' of the compressor when running in heating mode.
You've added a '+1' where you shouldn't have and boosted your expectations.
Here...
http://www.residential.carrier.com/products/acheatpumps/heatpumps/index.shtml
Carrier lists their top-of-the-line unit with an HPSF of "up to" 9.5. Since
HPSF is BTU/kw-hr you take that number and divide by 3.413 to get COPh.
That works out to a seasonal performance of only 2.78.
Of course the HPSF is a *seasonal* number and with a constant, mild supply
temperature the unit will perform better than that. But I seriously doubt
you could get anything like 5.
Air-source heat pumps are non-starters around here (too cold too often for
any meaningful COP). Only ground-source are worth looking at, but with a
warm water supply, a ground source pump should work fine and you can avoid
the expense of the ground loop.
> If you re-figure the case using these numbers then the heat pump
> option looks much better.
GIGO (Garbage-In / Garbage-Out). COP doesn't get as high as 4.0 much less
the 5.0 you want to claim. It would be a waste of time.
> The heat pump looks even better when
> electric rates are lower than yours (mine is a click under 8 cents)
> and gas is higher. (Chattanooga Gas
> http://www.chattanoogagas.com/Universal/RatesandTariff.aspx lists the
> first 25 therms at $1.3444/therm plus a $12/month "meter fee" as of
> this instant. Being summer, the fuel adjustment is slightly negative
> so the price per therm will be significantly higher in winter.)
> For folks heating with propane or oil, this would be a dream come
> true. I was just quoted $2.79/gallon for propane if I pay for the
> winter's supply now. Looks like I'll be skipping propane heat again
> this year. I'm lucky to have that option.
Of course those using propane often do so because they are too far away from
an urban area to make natural-gas piping economical. Same constraints might
make running 'warm water' piping equally un-economical.
<snip>
>>
>> OTOH, if the plant could supply me with water at 120 degF, I
>> wouldn't need a heat pump at all (saves me capital costs and some
>> maintenance), I could pay the full $250/month that I currently pay
>> for NG. (and of course my NG costs are expected to rise in the
>> coming years)
> I think that 120 deg water would require augmenting. 120 deg low
> humidity air is cold-feeling, as many an early heat pump user
> learned. Even the 140-150 deg air from my heat pump is at best,
> neutral feeling, neither particularly hot nor particularly cold. The
> reason air that hot doesn't feel warm is because the RH is near zero.
> My cabin typically runs 20% humidity in the winter at 70 deg. When
> air that dry is heated, the humidity drops to near zero, lower than
> my HVAC temperature/humidity instrument can measure.
20% RH at 70 F works out to a dew-point of about 28 F. Heat that air up to
110F and the RH drops to about 5.5%. My hi-efficiency natural-gas furnace
discharges air at about 115F when it's operating (I've got a couple years
worth of datalogs to prove it). With an outside dewpoint consistently in
the teens, that's an RH lower than yours. Yet it feels nice and comfy
coming out of the register, not 'cold feeling' at all. Maybe you just have
thin blood in your neck of the woods :-)
> Under-floor radiant heat might work with that cool a water supply.
> The radiant systems I have experience with usually run closer to 180
> deg. It would probably take special construction that put the water
> tubing right at the surface of the floor.
> Still, 120 deg water would be an excellent source of heat for a heat
> pump. A COPh of 5 or more would probably be possible.
The user costs would drop dramatically if the water temperature can be
raised to the point that only an air blower and small circulating pump are
needed.
That would make the 'warm water' much more valuable to the consumer and thus
better economics for the plant owner.
Just a tad warmer (say 135F) and you could use it for domestic hot-water as
well. Making it even more valuable to the consumer (imagine, no storage
tank and never running out of hot-water for the shower).
daestrom
Posted by Trygve Lillefosse on July 27, 2008, 8:32 pm
On Sat, 26 Jul 2008 12:56:27 -0400, "daestrom"
>Now, I pay about $1.25 / Therm for NG so that works out to about $250 /
>month in winter. If a heat pump runs at COP of 3 with this water, it would
>take about 1950 kW-hr a month to get the same 200 Therms and that would cost
>me about $253 / month ($0.13/kWh). So that leaves nothing to 'pay' for the
>use of the water. Nor the cost of my heat pump upgrade.
Sounds like you use a lot of electricity to heat your house...
You would not use a heatpump with distributed heating. You get it
straight into your house, circulate it and return it(trough the
return-pipe). Also, the price is diferentiated - if the return water
is too hot, you have to pay more. This is to encourage circulation in
the house rather than pumping it trough. (At least, this is the Danish
way of doing it.)
--
SEE YA !!!
Trygve Lillefosse
AKA - Malawi, The Fisher King
Posted by daestrom on July 28, 2008, 8:04 pm
Trygve Lillefosse wrote:
> On Sat, 26 Jul 2008 12:56:27 -0400, "daestrom"
>> Now, I pay about $1.25 / Therm for NG so that works out to about
>> $250 / month in winter. If a heat pump runs at COP of 3 with this
>> water, it would take about 1950 kW-hr a month to get the same 200
>> Therms and that would cost me about $253 / month ($0.13/kWh). So
>> that leaves nothing to 'pay' for the use of the water. Nor the cost
>> of my heat pump upgrade.
> Sounds like you use a lot of electricity to heat your house...
> You would not use a heatpump with distributed heating. You get it
> straight into your house, circulate it and return it(trough the
> return-pipe).
Well I agree with you there. But Neon John wants to distribute water at
only 50F (10C). That is too cold to heat hot-water or your home directly.
So he wants every house to have a heat-pump.
I think that route is a non-starter. Much better to raise the distributed
water temperature to 120-140F (50C to 60C) and use it directly as you state.
No need for a heat pump and it's capital/ operating / maintenance costs.
> Also, the price is diferentiated - if the return water
> is too hot, you have to pay more. This is to encourage circulation in
> the house rather than pumping it trough. (At least, this is the Danish
> way of doing it.)
How strange. Why would anyone *want* to 'pump it through' ? So is each
house charged based on flow and inlet/outlet differential (i.e. actual heat
used)??
daestrom
XML site map
>> the city to be used as the heat source for water-source heat pumps,
>> one still has to figure out how to pay for the plumbing. It surely
>> would not compete with simple ground-sourced heat pumps on an
>> economic basis.
>>
> I wrote the above as it popped into my head during a previous post.
> I've given it a couple hours' thought and I see some possibilities.
> A large power plant has a condenser cooling water flow rate measured
> in the millions of gallons per minute. The temperature rise through
> the condensers is in the 5 to 15 deg range, typically. Lots of
> slightly warmed water. The water is not hot enough to be useful for
> comfort heating but it DOES contain lots of low quality energy. A
> heat pump is a device that takes low quality heat and turns it back
> into higher quality heat. An idea is born.
> Suppose that a portion of or all of this water were diverted into
> canals, open or closed topped, that carry the warmed water to a
> nearby town. Homes and businesses along the canals could pump the
> water to water-sourced heat pumps. Or an alternative would be to put
> the refrigerant coil directly in the water if the house isn't too far
> away.