Heat pump ton conversion to FLA?

[Matt Mckenzie]

We are working with a heating and air contractor and we are wiring some new homes. The heating and air contractor always will only get us the tons information for example: 2 ton, 3 ton, 4 ton, etc. Trying to get the FLA from these guys is impossible. I usually just always start with a ten wire romex and go up to 8 wire for a 4 ton and 6 wire for a 5 ton. Is there any conversion or approximate conversion since getting the information from the heating and air contractor is impossible....?

 

[gadfly56]

We are working with a heating and air contractor and we are wiring some new homes. The heating and air contractor always will only get us the tons information for example: 2 ton, 3 ton, 4 ton, etc. Trying to get the FLA from these guys is impossible. I usually just always start with a ten wire romex and go up to 8 wire for a 4 ton and 6 wire for a 5 ton. Is there any conversion or approximate conversion since getting the information from the heating and air contractor is impossible....?

One ton of cooling is equal to 3.516 kilowatts. The term "ton" is the number of tons of water converted to ice in a 24 hour period. So at 4 tons, the unit will use about 14 kilowatts per day if it runs all day. You should be able to back calculate how many amps is being pulled. Please note that this is delivered capacity and make no allowance for cycle efficiencies, fan loads, etc.

 

[GoldDigger]

The one thing wrong with the above analysis is that the "ton" rating describes cooling output, while even mediocre AC units will move a quantity of heat per time that is several times their input power.
You can get a good ballpark though by looking at the input specs for a typical N ton unit.

 

[Galt]

One HP per ton is very close for air conditioners. Not for freezers.

 

[topgone]

We are working with a heating and air contractor and we are wiring some new homes. The heating and air contractor always will only get us the tons information for example: 2 ton, 3 ton, 4 ton, etc. Trying to get the FLA from these guys is impossible. I usually just always start with a ten wire romex and go up to 8 wire for a 4 ton and 6 wire for a 5 ton. Is there any conversion or approximate conversion since getting the information from the heating and air contractor is impossible....?

i am a bit rusty but lemme try.

1 ton of refrigeration = 12,000 BTU of heat

You don't convert that into watts directly because your compressor will be the one "pumping" that amount of heat out! You need to know how your heat pump uses electric power to do it, ask for the EER of your unit.

For your sake, let's assume your equipment has an EER of say, 10 BTU/watts (EER=10).
12,000 BTU/10 BTU per watt = 1,200 watts.

Now you do the rest of the calculations.

 

[texie]

We are working with a heating and air contractor and we are wiring some new homes. The heating and air contractor always will only get us the tons information for example: 2 ton, 3 ton, 4 ton, etc. Trying to get the FLA from these guys is impossible. I usually just always start with a ten wire romex and go up to 8 wire for a 4 ton and 6 wire for a 5 ton. Is there any conversion or approximate conversion since getting the information from the heating and air contractor is impossible....?

The only relevant and required information needed to properly size the conductors and the OCPD is the "MCA" and "Max OCPD" from the condensing unit. FLA, RLA, etc. are meaningless for these purposes. You size the conductors to the MCA and the breaker to the max OCPD.
But I understand your dilemma, as the HVAC guy never seems to have the info. on the unit until he sets it. To me, that is just an unacceptable answer, but I know it is rampant. This is a particular problem in an environment where there may be a number of houses involved. You can end up with a lot of homes with either undersized conductors, or in many cases oversized conductors that are just a waste of money.

 

[Smart $]

If this is your typical non-engineered residential, ask the HVAC contractors what brand of units they'll be installing. They usually stick with one, maybe two brands for which they are authorized retailers, or get the best deal on. You can then glean info from the brand's website documentation (if it's a reputable brand).

That said, you'll still likely get some surprises.

Don't know your particular contracting situation, but make sure revision costs (change orders) are written in your contract, especially for circumstances beyond your control as a result of other contractors' actions. Document your request for cut sheets from the HVAC contractor. When they start getting back charged for not providing the information requested, they'll change their tune when it gets costly.

 

[kwired]

We are working with a heating and air contractor and we are wiring some new homes. The heating and air contractor always will only get us the tons information for example: 2 ton, 3 ton, 4 ton, etc. Trying to get the FLA from these guys is impossible. I usually just always start with a ten wire romex and go up to 8 wire for a 4 ton and 6 wire for a 5 ton. Is there any conversion or approximate conversion since getting the information from the heating and air contractor is impossible....?

Some of the 5 ton units I have been connecting lately only needed 10 AWG (@75degC conductors, remember NM cable must be treated as 60C). They are getting more efficient as time goes by.