# How to determine BTU output of an electric pump

D

#### [email protected]

Jan 1, 1970
0
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 Fields

Jan 1, 1970
0
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.

L

#### linnix

Jan 1, 1970
0
And learn to do high school math.

1 BTU = 1055.05585 joules
1 Watt = 1 joule / second

W

#### WJLServo

Jan 1, 1970
0
And learn to do high school math.

1 BTU = 1055.05585 joules
1 Watt = 1 joule / second- Hide quoted text -

- Show quoted text -

Conversion factor from watts to BTU/hour all well and good, but, still
need to take into account efficiency of motor & pump. Presumably, some
of the 750 watt power draw is actually used to pump water, as opposed
to heating up case of motor....

W Letendre

J

#### John O'Flaherty

Jan 1, 1970
0
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.

0.75 kw/hr makes no sense, except as a rate of expansion of electric
utility capacity.

1 kWh = 3412 BTU
1 hp = 746 W = 0.746 kW

At 1 hp for 1 hour, the BTU equivalent is
0.746 kW * 1 hr * 3412 BTU / kWh = 2545 BTU.

At 230 V, 7.5 A, power is 1.725 kW.
for 1 hour, this is 5886 BTU.

The differences are accounted for by whether the figures are ratings
or figures about actual operation, and efficiency - shaft power
delivered vs. total power consumed. I'm not sure what you mean by
"given off". Is this a heat loss figure?

W

#### WJLServo

Jan 1, 1970
0
0.75 kw/hr makes no sense, except as a rate of expansion of electric
utility capacity.

1 kWh = 3412 BTU
1 hp = 746 W = 0.746 kW

At 1 hp for 1 hour, the BTU equivalent is
0.746 kW * 1 hr * 3412 BTU / kWh = 2545 BTU.

At 230 V, 7.5 A, power is 1.725 kW.
for 1 hour, this is 5886 BTU.

The differences are accounted for by whether the figures are ratings
or figures about actual operation, and efficiency - shaft power
delivered vs. total power consumed. I'm not sure what you mean by
"given off". Is this a heat loss figure?

I certainly would have guessed that the OP was looking to calculate
heating; BTUs are seldom used to measure anything else, and, as you
say, the term "given off" is evocative...

Maybe the OP was looking to size air conditioner for pump shed?

WAG would be that motor on this rig runs ~ 85% efficient under load.
Pump probably wastes another 10-20% of power in fluid flow viscous
losses, but, that heat load will be carried out to the swimming pool
in the water flow. Leaves (VERY roughly) either 380 or 880 BTU/hr,
give or take, as heat dissipated by motor, depending on whether 1 hp
or 1.725 KW is the motor's true power rating.

W Letendre

J

#### Jim Thompson

Jan 1, 1970
0
I certainly would have guessed that the OP was looking to calculate
heating; BTUs are seldom used to measure anything else, and, as you
say, the term "given off" is evocative...

Maybe the OP was looking to size air conditioner for pump shed?

WAG would be that motor on this rig runs ~ 85% efficient under load.
Pump probably wastes another 10-20% of power in fluid flow viscous
losses, but, that heat load will be carried out to the swimming pool
in the water flow. Leaves (VERY roughly) either 380 or 880 BTU/hr,
give or take, as heat dissipated by motor, depending on whether 1 hp
or 1.725 KW is the motor's true power rating.

W Letendre

My swimming pool equipment "shed" is surrounded on three sides, the
house and an approximately 5' block wall (stuccoed like the house).

Temperature rise from a 2HP pump is ~7°F :-(

...Jim Thompson

T

#### Terry Given

Jan 1, 1970
0
WJLServo said:
I certainly would have guessed that the OP was looking to calculate
heating; BTUs are seldom used to measure anything else, and, as you
say, the term "given off" is evocative...

Maybe the OP was looking to size air conditioner for pump shed?

WAG would be that motor on this rig runs ~ 85% efficient under load.
Pump probably wastes another 10-20% of power in fluid flow viscous
losses, but, that heat load will be carried out to the swimming pool
in the water flow. Leaves (VERY roughly) either 380 or 880 BTU/hr,
give or take, as heat dissipated by motor, depending on whether 1 hp
or 1.725 KW is the motor's true power rating.

its 1.725kVA, 750W so a very low PF. in which case the efficiency is
probably more like 70%. little motors have a favourable
surface-area-to-volume ratio, so tend to be designed to be as cheap (IOW
as lossy) as possible (NB modern motor standards are stomping out this
sort of shitty design practice), as they can get rid of the heat. so
somewhere between 300 & 400 BTU (Bloody Terrible Unit)

Cheers
Terry

C

#### Clifford Heath

Jan 1, 1970
0
WJLServo said:
...Leaves (VERY roughly) either 380 or 880 BTU/hr,
give or take, as heat dissipated by motor, depending on whether 1 hp
or 1.725 KW is the motor's true power rating.

The actual current drawn will depend on whether the pump rotor is
designed to draw the motor's full power. It's likely actually a
bit undersized, and the only way to know the actual consumption
is to measure the current/voltage, i.e. a wattmeter. It will vary
a lot depending on whether the filter needs backwashing too.

Clifford Heath.

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