Heat load due to conveyor motors
Heat load due to conveyor motors
(OP)
Ok, I feel really dumb about this. It seems like it should be straight forward, but I can't wrap my head around it.
I have a project with about 250 hp of conveyor motors. These conveyors move product both horizontally and vertically. Eventually, one of the conveyors moves the product out of the warehouse at a higher elevation than it comes in.
My question is: Does all the heat from the conveyor motors become part of the A/C load? I understand that if it was a chilled water pump, a fan or an air compressor I would include it all in the A/C load.
But I am getting confused in my head because of the change in potential energy of the product (due to elevation change) leaving the warehouse.
I have a project with about 250 hp of conveyor motors. These conveyors move product both horizontally and vertically. Eventually, one of the conveyors moves the product out of the warehouse at a higher elevation than it comes in.
My question is: Does all the heat from the conveyor motors become part of the A/C load? I understand that if it was a chilled water pump, a fan or an air compressor I would include it all in the A/C load.
But I am getting confused in my head because of the change in potential energy of the product (due to elevation change) leaving the warehouse.





RE: Heat load due to conveyor motors
RE: Heat load due to conveyor motors
If a fan is blowing air, the heat from the motor and the velocity of the air all ends up being converted to heat. This I understand.
However, if in the conveyor, all the energy is converted to heat in the motor...WHERE does the energy to change the elevation of the product come from?
The energy of the moving air turns to heat, but the potential energy of the elevated product does not. This seems to me to not be an equivalent treatment of energy.
RE: Heat load due to conveyor motors
What goes in must come out. More power goes in than what is required to do the lifting. So friction and heat from the ineffciency of the motor will heat the space.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
But is all of this heat really rejected to the space? And now that I think about it, I don't fully understand my conversion number of 2,542BTUH/HP. I took it from a book, but how does it account for motor efficiency? A less efficient motor will consume more energy and give off more heat, right?
I'm confused too.
RE: Heat load due to conveyor motors
That table shows for 'motor & driven equipment' in the conditioned space the gain on a 250 hp motor (91%) efficient is 699,000 so take your number divided by 0.91 and you are right there.
AHSRAE is basically using the motor power divided by efficiency times a fudge factor for how frequently it runs, where 1 would be continuous and as well as a factor for how loaded that motor is and the load factor would get into the service factor at times THEREFORE GREATER THAN 1.
Table 3A shows them fully loaded with both the motor and the driven equipment in the space, with the driven equipment in the space and motor not in the space, and with the motor in the space and the driven equipment out of the space.
The motor in the space only, the gain on the 250 hp motor is 62,900 Btu/hr got to be the efficiency here, 699,000x.09=62910.
With a horizontal conveyor rolling along loaded, what is the motor power doing after the belts are started and inertia is over come? It is over coming the friction of the conveyor (like rolling losses of car, the bearings, drive losses), the friction of the loaded conveyor on the rollers, plus air drag on the load. So when all friction losses are in the space there is heat to the space.
Loaded belt more rolling losses, more weight on the (for lack of a better word) rollers, plus air drag. Belt is running empty, less weight down on those rollers so less friction, less air drag. Less power the motor draws.
With the inclined belts and vertical 'legs' lifting the load there is also the friction mentioned above. I do not see the energy of the lift itself creating heat outside of the heat shed at the motor.
Smaller motors are less efficient than the big motors.
I spent a few years in grain elevators and at times the equipment ran steady such as when loading 30,000 tons on a ship or other times it was infrequent and very intermittent. Some belts ran steady but were unloaded the majority of the time.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
I have strayed from MAragorn's original question of potentieal energy. The motor is working harder to raise the product than to simple convey it horizontally, but both motor and driven equipment are in the conditioned space, so it would seem that all of the heat is rejectrd into the space.
Now one more question. Let's take 250HP for example from table 3A. With both motor and driven equipment in the conditioned space, the heat is 699,000BTUH. With the motor out and the driven eqipment in, the heat is 636,000 BTUH. Now where is this heat? Is it the motor heat that is not in the conditioned space, or is it the heat from the driven equipment that is in the the conditioned space?
RE: Heat load due to conveyor motors
I have the 2001 ashrae handbook, but I can't find the chapter you are reffering to. Am I in the right book?
thanks,
RE: Heat load due to conveyor motors
RE: Heat load due to conveyor motors
The 636,000 is the work done by the motor on the driven equipment in the space, what you would allow for in a cooling load. The 62,900 is outside of the conditioned space, similar to a big monster air handler with the shaft extending out of the casing and the motor out of the airstream.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
So to be clear, if the 250 HP motor is OUT of the conditioned space and the driven equipment in IN the space, I would add 636,000 to the air conditioning load of the space. Correct?
Conversly, if the motor is IN the conditioned space and the driven equipment is OUT, I would only add 62,900 to the air conditioning load. Correct?
This is counter-intuitive to me because I would think that the motor would always be a larger heat source than whatever equipment it may be driving.
RE: Heat load due to conveyor motors
In this case, both the motor and the driven equipment are in the space, so the complete load is added to the A/C load.
I may have accidentally misled, in that there are a number of smaller convetors in series, each with its own motor, all totalling 250 HP.
I believe that ONLY the portion of the work of the last conveyor that elevates the product prior to leaving the building would NOT be part of the HVAC load. Except for that all motor loads are included in the A/C load.
RE: Heat load due to conveyor motors
That is my take on it
Conversly, if the motor is IN the conditioned space and the driven equipment is OUT, I would only add 62,900 to the air conditioning load. Correct?
Correctamundo again fonzie
This is counter-intuitive to me because I would think that the motor would always be a larger heat source than whatever equipment it may be driving.
I think that heat coming off of the motor casing is the inefficiency. That 250 hp example said it was a 91% efficient motor, 699x.91=636, what's left over?
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
Smaller motors tend to be less efficient than the larger ones. They all run steady at the same time?
I believe that ONLY the portion of the work of the last conveyor that elevates the product prior to leaving the building would NOT be part of the HVAC load. Except for that all motor loads are included in the A/C load.
My gut feeling is it will radiate a little more heat off of the casing than the horizontal ones, I don't think it really adds any more heat from the work than the horizontal ones, I guess if you knew how many pounds per hour it was lifting you could correct.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
RE: Heat load due to conveyor motors
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
It is sort of like in the days where they were boring cannon barrels under water to come up with work makes heat
http://www
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
ASHRAE 2005 HOF says, as the no load power of motor is generally high, we have to follow the equations without any reduction (or atleast that is what I understood from the book). Check the same page as that of motor heat loads.
RE: Heat load due to conveyor motors
I think the pump motor would be like the 'motor in the space'. Hermetic compressors have their winidngs cooled by refrigerant but the dome can be quite hot and so can some of the discharge piping. I would think treating it as motor in and driven load out would be conservative.
Last hydraulic elevator submittal I had, gave a much higher heat output compared to the "motor in, driven equipment out", however a cooling system sized only for the "motor in" is keeping up. Most likely luck that the elevator is not heavily used.
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
Take the "V" out of HVAC and you are left with a HAC(k) job.
RE: Heat load due to conveyor motors
I took the mechanical room as an example. If the full motor load is carried out by the room air then you could downsize the cooling tower to just take care of the conditioned space heat load. However, BHP is associated with the increase in refrigerant enthalpy(first) and this is carried away by the cooling water, rather.
The link given by imok2 discusses the OP's issue to some extent. I request you to have a look into that.
Heat output from the elevator may differ during upward and downward movements. My gut feeling is that there should be more heat output during downward transit.
Having said that, as a conservative approach, I will consider ASHRAE's equations. A bit of pep talk and leg pulling adds some heat load to otherwise cold forum