Heat load dye to Reach truck in cold store

[smpsmp45]

How much should be the heat added due to operation of battery operated Reach truck in the cold store? The battery rating is 375Ah( Amp Hour).

One may have to assume some No of hours for the reach truck to be in the cold store?

[Plank!]

It would be easier to calculate if you gave the battery voltage not just the Ah.

Typical reach truck batteries are 72VDC but could be as high as 96VDC

375 x 72 = 27,000 W/H

FLT drive motor will be 3KW max, lift pump 1.3KW max, steering pump 500W max. NOT all operating at the same time. the battery is nomally sized for an 8 hour shift. (or less if it has a heated cab.)

So 3 - 5KW should be about right.

Also remember the truck could have been at ambient temp before entering the store, so now you have a 3ton+ mass of steel driving around the store radiating heat - most reach trucks will leave the store between shifts, but at very least i would expect to see it leave for battery charge and service.

[nh3wizard]

How much should be the heat added due to operation of battery operated Reach truck in the cold store? The battery rating is 375Ah( Amp Hour).

One may have to assume some No of hours for the reach truck to be in the cold store?

I have never actually given it much thought, why would you want to know?

[US Iceman]

Sounds like someone is doing heat load calculations. There ought to be something in the ASHRAE Refrigeration handbook. If I can find some spare time this weekend, I will have a look.

[nh3wizard]

I never acutally thought of adding the heat load from reach trucks into the heatload calculations, it just seems it would be hard due to not knowing how long trucks would be in the refrigerated area. Just something Ill have look at closer.

[US Iceman]

Well, it's like a lot of things we encounter.

Just about any calculation is based on assumptions used. In this case, it would apply to the estimated energy output of the fork truck and the estimated time the fork truck would be in the cold space.

We have the same issue with people in the cold space, lights, etc.

[nike123]

According to Calc-Rite software 1570 Btu/hr.

Sorry, I did not cleared some fields about lighting and therefore this value is not OK.
When corrected i have this number
302,16W (1031Btu/hr) for one forklift, per hour of lift activity.

Then, here I found 10.200 W/h for 8 hr!
http://www.ba.ars.usda.gov/hb66/012heat.pdf

Also I found this data:
4250 Btu/HP for motors under ½ HP, 3700 Btu/HP for larger motors
http://www.agf.gov.bc.ca/resmgmt/pub...s/306300-3.pdf

[smpsmp45]

I have checked in the cold store manual & tha does specify the Load has to considered for heat load calculations. We are working as a consultant for a project & we need to justify the heat load calculations. Though when we had done the projects, we never calculated this load & it was assumed that in the safety factor that load is considered. But as Plank has said, it has to be added upto 5 KW. Even the mass of the Reach truck at ambient is going to add extra load. Many thanks Plank for the right answer.

[smpsmp45]

Even nike123 has given a figure based on a software & that is interesting.

[Sergei]

It isn't simple question. Part of this energy used to move the truck and the product. Energy for this actions won't be released in refrigerated space and this isn't refrigeration load. Look at compressor room. Compressor el. motor is 95% efficient. It means that 95% energy used to compress refrigerant and 5% will be released in compressor room. From 5 Kw energy part will be used to move truck and product(no heat released) and part will be released as heat.

[US Iceman]

In regards to Sergei's comment here is another interesting twist. How much energy from an evaporator fan goes into the space? Assume the fan motor is in the space....

[Sergei]

Usually, energy used to do a work. Part of this energy is wasted. For water pump, 95% of energy spent to move the water and this energy will increase water temperature(may be just 0.1C or less). 5% will be wasted by el. motor and will be released as a heat in surrounding air. For evaporator fans these two energy flows will go to surrounding air and all energy will be transferred to the air.

[US Iceman]

For evaporator fans these two energy flows will go to surrounding air and all energy will be transferred to the air.

I agree, which is why I think this is similar to the forklifts. The energy used for electric motors and hydraulics on the lifts is all within the space.

[Sergei]

Another example. Conveyor located in the freezer. It moves boxes. El.motor is 95% efficient. 5% energy goes to the freezer as heat load. 95% energy used to move boxes.

[US Iceman]

Here are my thoughts on this (for what they are worth, but remember they are free!).

If the energy produced by a motor is within the temperature controlled space, the energy becomes part of the total heat load.

If the motor is located within the space, it's heat due to motor efficiency is also part of the heat load.

If the motor is located outside of the space, it's heat due to motor efficiency is not part of the heat load.

Stacker cranes, conveyors, forklifts, etc.

Fan motors in a space are interesting because their current draw is higher than standard air conditions (which is what their rating is based on). So, you have to correct for higher air density.

[Plank!]

Looks like most of us are giving different answers here, Sergei does have a point about motor efficiency, but the motor is not the only component producing heat, All forklift motors are electronically controlled so there is also a heat component from the drive electronics (maybe 80% efficient) the battery also heats when discharging, the hydraulic oil is warmed by the pump and pressures involved in lifting, the controls are usually fitted with anti condensation heaters, some coldstore trucks have heated seats or cabs.

While motors can be 95% efficient I doubt any fork truck manufacturer will claim anything like 95% efficiency for the truck.

I based my figures on personal experience dealing with fork trucks when i was a site engineer, since then technology has changed a little, most trucks now use AC motors driven by invertors - probably more efficient than the MOSFET DC controllers i was used to. However the figures i gave are peak loads, in practice the motors will not be driven that hard for more than a few % of the time in the store.

I guess the only correct answer would be to contact the fork truck manufacturer and get model specific data