Cooling Load Calculations

[hamidpia]

For cooling load calculations, while taking into consideration Electric Motor Load, ASHRAE Handbook Chapter 30.7 for Non residential cooling and heating load calculations, gives maximum load while driven equipment is in the conditioned space. e.g for for 7.5hp motor it gives in btu/hr 1. Motor in driven equipment in 22700, 2. motor out driven equipment in 19100,3. Motor in driven equipment out 3640. What I fail to understand, does driven equipment generate more heat that motor itself, which is consuming energy, producing IR losses (Heat Losses). If motor only is in conditioned space, according to book, it generates least amount of heat. Please let me know where I am wrong. I know hand book can not be wrong.
Thanks and best regards

[Brian_UK]

With 'Motor IN driven...' do they mean that the motor is internal to the equipment?

Such as inside a semi or hermetic compressor or even a ventilation fan.

A 'Motor OUT...' could be a belt driven item for example.

[wambat]

For cooling load calculations, while taking into consideration Electric Motor Load, ASHRAE Handbook Chapter 30.7 for Non residential cooling and heating load calculations, gives maximum load while driven equipment is in the conditioned space. e.g for for 7.5hp motor it gives in btu/hr 1. Motor in driven equipment in 22700, 2. motor out driven equipment in 19100,3. Motor in driven equipment out 3640. What I fail to understand, does driven equipment generate more heat that motor itself, which is consuming energy, producing IR losses (Heat Losses). If motor only is in conditioned space, according to book, it generates least amount of heat. Please let me know where I am wrong. I know hand book can not be wrong.
Thanks and best regards

Hamidpia
1. If you have both the motor and the driven equipment in the conditioned space then the heat load is 22700
2. If the motor is out but the driven equipment is in the conditioned space then the heat load is 19100
3. If only the motor is in the the conditioned space then the heat load is 3640 btu/hr

[hamidpia]

Dear wambat, I that is true but my question is that motor is the equipment that is generating heat and cosuming energy to produce heat losses like (I)2R losses and that is producing less heat load, whereas driven equipment does consume any energy and is producing more heat. I fail to understand this. Brain answer more logical. One thing, could there be so much of difference by enclosing and exposing motor. almost 8 times.

[canyon]

Hi friends,

I am new in this site. I am a research student and am doing some cooling load calculations. I am looking for a journal article which seems not available anywhere. I would be grateful if anybody could help me to find it. it is: Milbank. NO. & Harrington-Lynn. J. (1974): Thermal Response and the Admittance Procedure: BRE CP 61/74.

thanks very much for your help

[mikendab]

Hi all
Just seen this message today and hope to contribute. not sure if you have got solutions to the actual problem raised.
The solution is simple. if you have a motor driving a machine, the motor has heat losses but the main heat will be generated in the machine. take for a example a compressor in a refrigeration system, the motor drives the compressor, the compressor develops the heat of compression that is added to the cooling load and this is rejected inthe condenser. In simple terms if you take the temerature of a motor driving a compressor, the motor will not be as hot as the compressor head.
so the machine will always generate more heat than the motor.
therefore as the design guide says if you have the motor and machine in the space to be conditioned ie in could be a hermetic compressor or belt driven compressor where the motor and drive are in the space to be conditioned then max load of 22700Btu/hr. if only the machine is in the space , iit could be a belt drive or shaft drive where the compressor is in the space and motor is out then use on 19100. however if only the motor is in the space. a rare occurence then use only the heat loss in the motor.3640 Btu/h.

[Toosh]

Hi friends,

I am new in this site. I am a research student and am doing some cooling load calculations. I am looking for a journal article which seems not available anywhere. I would be grateful if anybody could help me to find it. it is: Milbank. NO. & Harrington-Lynn. J. (1974): Thermal Response and the Admittance Procedure: BRE CP 61/74.

thanks very much for your help

There is a Search engine called GOOGLE I suggest you try looking for it yourself

Norm

[frank]

Hi all
Just seen this message today and hope to contribute. not sure if you have got solutions to the actual problem raised.
The solution is simple. if you have a motor driving a machine, the motor has heat losses but the main heat will be generated in the machine. take for a example a compressor in a refrigeration system, the motor drives the compressor, the compressor develops the heat of compression that is added to the cooling load and this is rejected inthe condenser. In simple terms if you take the temerature of a motor driving a compressor, the motor will not be as hot as the compressor head.
so the machine will always generate more heat than the motor.
therefore as the design guide says if you have the motor and machine in the space to be conditioned ie in could be a hermetic compressor or belt driven compressor where the motor and drive are in the space to be conditioned then max load of 22700Btu/hr. if only the machine is in the space , iit could be a belt drive or shaft drive where the compressor is in the space and motor is out then use on 19100. however if only the motor is in the space. a rare occurence then use only the heat loss in the motor.3640 Btu/h.

have you looked at the latest generation of Daikin compressors?

They are 'Hot Gas Cooled'. The hot gas is cooler than the motor and is re-cycled through the motor to increase superheat, as well as providing motor cooling.