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Getting a more efficient heat pump Jud McCranie 09-18-2007
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Posted by Jud McCranie on September 18, 2007, 7:47 pm
I'm trying to estimate how long it would take to recoup my investment
if I buy a more efficient heat pump.

The one we have is 11 years old and has a SEER of 10.05. It is a
4-ton unit for about 1975 square feet and the real estate agent said
that it was oversized, so me might could use a smaller one.

I got my monthly electric bills for the past 12 months. We used a
total of 27,100 kWh, at a cost of $2,574. Our rate depends on the
season and also on how much you use in a month. Summer rates are
higher, and the more you use, the more it cost.

There are periods in the fall and spring where very little heating and
cooling is used. Our smallest bill was in November, using 1600 kWh,
at a cost of $129. If I assumed that this used no heat/cooling, that
means that heating and cooling came to 7,900 kWh, or $1026.

Does that look like I could recoup my investment in a more efficient
heat pump in, say, five years?
--
Replace you know what by j to email

Real Goods Solar, Inc.
Posted by Robert Allison on September 18, 2007, 9:40 pm
Jud McCranie wrote:

> I'm trying to estimate how long it would take to recoup my investment
> if I buy a more efficient heat pump.
>
> The one we have is 11 years old and has a SEER of 10.05. It is a
> 4-ton unit for about 1975 square feet and the real estate agent said
> that it was oversized, so me might could use a smaller one.
>
> I got my monthly electric bills for the past 12 months. We used a
> total of 27,100 kWh, at a cost of $2,574. Our rate depends on the
> season and also on how much you use in a month. Summer rates are
> higher, and the more you use, the more it cost.
>
> There are periods in the fall and spring where very little heating and
> cooling is used. Our smallest bill was in November, using 1600 kWh,
> at a cost of $129. If I assumed that this used no heat/cooling, that
> means that heating and cooling came to 7,900 kWh, or $1026.
>
> Does that look like I could recoup my investment in a more efficient
> heat pump in, say, five years?

Your real estate agent also does air conditioning?

Let the HVAC guys size your unit. That said, savings depend
upon a lot of factors, far too many to review right here. You
can get an idea of the savings based on the chart at this site:

http://www.ehwhitson.com/seer_rating.htm

Just upsize by 25% and that should tell you what you want to know.

--
Robert Allison        
Rimshot, Inc.
Georgetown, TX

Posted by CJT on September 18, 2007, 10:40 pm
Robert Allison wrote:

> Jud McCranie wrote:
>
>> I'm trying to estimate how long it would take to recoup my investment
>> if I buy a more efficient heat pump.
>>
>> The one we have is 11 years old and has a SEER of 10.05. It is a
>> 4-ton unit for about 1975 square feet and the real estate agent said
>> that it was oversized, so me might could use a smaller one.
>>
>> I got my monthly electric bills for the past 12 months. We used a
>> total of 27,100 kWh, at a cost of $2,574. Our rate depends on the
>> season and also on how much you use in a month. Summer rates are
>> higher, and the more you use, the more it cost.
>>
>> There are periods in the fall and spring where very little heating and
>> cooling is used. Our smallest bill was in November, using 1600 kWh,
>> at a cost of $129. If I assumed that this used no heat/cooling, that
>> means that heating and cooling came to 7,900 kWh, or $1026.
>>
>> Does that look like I could recoup my investment in a more efficient
>> heat pump in, say, five years?
>
>
> Your real estate agent also does air conditioning?
>
> Let the HVAC guys size your unit. That said, savings depend upon a lot
> of factors, far too many to review right here. You can get an idea of
> the savings based on the chart at this site:
>
> http://www.ehwhitson.com/seer_rating.htm
>
> Just upsize by 25% and that should tell you what you want to know.
>
From that page:

"The following data is based on a 3-ton system (36,000 BTUH) at 9 cents
per KWH at 2800 annual hours of use."

2800 annual hours of use? I hope they don't mean that's how many hours
they assume it runs in a year. Even on a hot day here in Texas, our
unit only runs about 10 hours. And while it's warm here much of the
year, the heavy AC season is only about 4 months long. Maybe if I have
some spare time, I'll add up the minutes our AC ran last year (I have it
instrumented); I'm pretty sure it's nowhere near 2800 hours.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

Posted by on September 18, 2007, 10:47 pm

> Robert Allison wrote:
>
> > Jud McCranie wrote:
> >
> >> I'm trying to estimate how long it would take to recoup my investment
> >> if I buy a more efficient heat pump.
> >>
> >> The one we have is 11 years old and has a SEER of 10.05. It is a
> >> 4-ton unit for about 1975 square feet and the real estate agent said
> >> that it was oversized, so me might could use a smaller one.
> >>
> >> I got my monthly electric bills for the past 12 months. We used a
> >> total of 27,100 kWh, at a cost of $2,574. Our rate depends on the
> >> season and also on how much you use in a month. Summer rates are
> >> higher, and the more you use, the more it cost.
> >>
> >> There are periods in the fall and spring where very little heating and
> >> cooling is used. Our smallest bill was in November, using 1600 kWh,
> >> at a cost of $129. If I assumed that this used no heat/cooling, that
> >> means that heating and cooling came to 7,900 kWh, or $1026.
> >>
> >> Does that look like I could recoup my investment in a more efficient
> >> heat pump in, say, five years?
> >
> >
> > Your real estate agent also does air conditioning?
> >
> > Let the HVAC guys size your unit. That said, savings depend upon a lot
> > of factors, far too many to review right here. You can get an idea of
> > the savings based on the chart at this site:
> >
> > http://www.ehwhitson.com/seer_rating.htm
> >
> > Just upsize by 25% and that should tell you what you want to know.
> >
> From that page:
>
> "The following data is based on a 3-ton system (36,000 BTUH) at 9 cents
> per KWH at 2800 annual hours of use."
>
> 2800 annual hours of use? I hope they don't mean that's how many hours
> they assume it runs in a year. Even on a hot day here in Texas, our
> unit only runs about 10 hours. And while it's warm here much of the
> year, the heavy AC season is only about 4 months long. Maybe if I have
> some spare time, I'll add up the minutes our AC ran last year (I have it
> instrumented); I'm pretty sure it's nowhere near 2800 hours.


The best way to figure operational cost is too use the areas Cooling/Heating
degree days and know what size unit you are going to be operating.
Have that and the cost of your utilities, you can get very close to the
actual operational cost.



Posted by CJT on September 18, 2007, 10:53 pm
CJT wrote:

> Robert Allison wrote:
>
>> Jud McCranie wrote:
>>
>>> I'm trying to estimate how long it would take to recoup my investment
>>> if I buy a more efficient heat pump.
>>>
>>> The one we have is 11 years old and has a SEER of 10.05. It is a
>>> 4-ton unit for about 1975 square feet and the real estate agent said
>>> that it was oversized, so me might could use a smaller one.
>>>
>>> I got my monthly electric bills for the past 12 months. We used a
>>> total of 27,100 kWh, at a cost of $2,574. Our rate depends on the
>>> season and also on how much you use in a month. Summer rates are
>>> higher, and the more you use, the more it cost.
>>>
>>> There are periods in the fall and spring where very little heating and
>>> cooling is used. Our smallest bill was in November, using 1600 kWh,
>>> at a cost of $129. If I assumed that this used no heat/cooling, that
>>> means that heating and cooling came to 7,900 kWh, or $1026.
>>>
>>> Does that look like I could recoup my investment in a more efficient
>>> heat pump in, say, five years?
>>
>>
>>
>> Your real estate agent also does air conditioning?
>>
>> Let the HVAC guys size your unit. That said, savings depend upon a
>> lot of factors, far too many to review right here. You can get an
>> idea of the savings based on the chart at this site:
>>
>> http://www.ehwhitson.com/seer_rating.htm
>>
>> Just upsize by 25% and that should tell you what you want to know.
>>
> From that page:
>
> "The following data is based on a 3-ton system (36,000 BTUH) at 9 cents
> per KWH at 2800 annual hours of use."
>
> 2800 annual hours of use? I hope they don't mean that's how many hours
> they assume it runs in a year. Even on a hot day here in Texas, our
> unit only runs about 10 hours. And while it's warm here much of the
> year, the heavy AC season is only about 4 months long. Maybe if I have
> some spare time, I'll add up the minutes our AC ran last year (I have it
> instrumented); I'm pretty sure it's nowhere near 2800 hours.
>
I realized I could get at the number another way (I know about how many
KWH I use for cooling each year, and about how many watts the AC and
air handler consume while running). In a year, our AC runs about 1600
hours. 2800 seems way high to me.

Austin, Texas

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

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