# How to determine how many BTU's are given off by an electric motor

D

#### [email protected]

Jan 1, 1970
0
Hello,

I have an electric pool pump and am trying to figure out how many
BTU's are given off during normal operation (let's say 1 hour). The
specs are as follows:

1hp
RPM 3450
230v @ 7.5 amps
0.75kw/hr

I was told that there should be some formula to find this out; however
I cannot seem to find it. Any help would be great.

Thanks,
Doug

J

#### John Popelish

Jan 1, 1970
0
Hello,

I have an electric pool pump and am trying to figure out how many
BTU's are given off during normal operation (let's say 1 hour). The
specs are as follows:

1hp
RPM 3450
230v @ 7.5 amps
0.75kw/hr

I was told that there should be some formula to find this out; however
I cannot seem to find it. Any help would be great.

Based on normal motor efficiency around 75 to 80%, you can
probably estimate that the motor will produce a waste heat
of about 1/4 of its rated mechanical output. A horsepower
is 770 watts, so the waste heat is about 770/4 about 200
watts goes into the air cooling the motor. Of course all
the mechanical output also gets converted to heat in the
pool water as friction, so about 770 watts goes into the water.

J

#### John Fields

Jan 1, 1970
0
Hello,

I have an electric pool pump and am trying to figure out how many
BTU's are given off during normal operation (let's say 1 hour). The
specs are as follows:

1hp
RPM 3450
230v @ 7.5 amps
0.75kw/hr

I was told that there should be some formula to find this out; however
I cannot seem to find it. Any help would be great.

A

#### Anonymous.

Jan 1, 1970
0
John Fields said:
1 kilowatt-hour = 3413 BTU

You need to be careful as to what you refer .........

BTU = Board Of Trade Unit = Kilowatt Hour

BThU = British Thermal Unit, which ISTR is energy needed to
raise 1 lb of water by 1 degree F.

D

#### Dan Coby

Jan 1, 1970
0
A horsepower is 770 watts,

The usual conversion factor that I have seen is ! hp = 746 watts. I did a
check in wikipedia and they give 745.699 871 582 270 22 watts. They
also give different types of horsepower, (imperial, metric) with slightly
different conversion factors (746 vs 736 watts).

http://en.wikipedia.org/wiki/Conversion_of_units#Power

J

#### John Fields

Jan 1, 1970
0
You need to be careful as to what you refer .........

BTU = Board Of Trade Unit = Kilowatt Hour

BThU = British Thermal Unit, which ISTR is energy needed to
raise 1 lb of water by 1 degree F.

---
Hmm...

BTU as an acronym for "British Thermal Unit" is hardly deprecated,
as indicated by Wikipedia at:

http://www.wisegeek.com/what-is-a-btu.htm

and Webster's at:

http://www.websters-online-dictionary.org/definition/BTU

Moreover, from the context of the article it should have been
abundantly clear that the OP was asking for a conversion from
watt-hours to British Thermal Units, so what's your point?

T

#### terryS

Jan 1, 1970
0
Hello,

I have an electric pool pump and am trying to figure out how many
BTU's are given off during normal operation (let's say 1 hour). The
specs are as follows:

1hp
RPM 3450
230v @ 7.5 amps
0.75kw/hr

I was told that there should be some formula to find this out; however
I cannot seem to find it. Any help would be great.

Thanks,
Doug

Answering this question per the above info.
1) 230 x 7.5 = 1725 watts.
2) But one horespower is 746 watts.
3) So item one maybe the starting current?
Using that it IS a 'one' horsepower motor which at 230 volts will have
a 'running' current of 746/230 = 3.2 amps.
4) If the motor has typical efficiency of 75%; 25% of the (one
horsepower) wattage is dissipated as electrical heat.
5) 746 x 0.25 = 186.5 watts.
6) 1000 watts = 3413 BTU (British Thermal Units).
7) Therefore 186.5/1000 x 3413 = 636.5 BTU, dissipated as electrical
heat by the motor itself.

J

#### [email protected]

Jan 1, 1970
0
"John Popelish" <[email protected]> wrote in message
The usual conversion factor that I have seen is ! hp = 746 watts. I did a
check in wikipedia and they give 745.699 871 582 270 22 watts. They
also give different types of horsepower, (imperial, metric) with slightly
different conversion factors (746 vs 736 watts).

http://en.wikipedia.org/wiki/Conversion_of_units#Power

By the time i realized that I had remembered the factor wrong, others

The point to make is that just entering BTU or HP into Google gives
the conversion factors at the top.

But thanks for the help.

J

#### [email protected]

Jan 1, 1970
0
The point to make is that just entering BTU or HP into Google gives
the conversion factors at the top.

Correction: you have to enter [horsepower] to get the conversion
factor.

R

#### redbelly

Jan 1, 1970
0
Answering this question per the above info.
1) 230 x 7.5 = 1725 watts.
2) But one horespower is 746 watts.
3) So item one maybe the starting current?
Using that it IS a 'one' horsepower motor which at 230 volts will have
a 'running' current of 746/230 = 3.2 amps.
4) If the motor has typical efficiency of 75%; 25% of the (one
horsepower) wattage is dissipated as electrical heat.
5) 746 x 0.25 = 186.5 watts.
6) 1000 watts = 3413 BTU (British Thermal Units).

Just FYI, that should be 1000 Watt-hours = 3413 BTU
7) Therefore 186.5/1000 x 3413 = 636.5 BTU, dissipated as electrical
heat by the motor itself.

.... per hour.

Mark

T

#### terryS

Jan 1, 1970
0
Just FYI, that should be 1000 Watt-hours = 3413 BTU

... per hour.

Mark- Hide quoted text -

- Show quoted text -

Yup. Just revisited this thread. Your right man. 1000 watt hours it
is.
i.e. One kilowatt hour or one 'unit' in some jurisdictions.

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