power rating in the nameplate 6

[meroelme]

Does the power rating at the back or nameplate of an airconditioning unit if converted to tons of refrigeration (TOR) can cool a space of the same TOR?

For example, if the nameplate has a power rating of say 3.517 kW and if converted to TOR is equivalent to 1 tons. Does this mean that it can extract 1 ton of heat in the space?

If so, are all ac units 100% efficient?

 

[MintJulep]

No.

 

[meroelme]

What does "no" mean? Is it an answer to my first question, the second, or both?

If both, then if I calculated a space heat load of about 1ton, what type of ac unit should I buy? I mean what nameplate rating should I choose?

 

[EnergyProfessional]

name plate rating probably is tested under ARI standard conditions. Your space load may be under different conditions (i.e. higher ambient temperature). the manufacturer can get you a ambient relief curve.

I assume you just talk about a 2 ton residential unit, then just use that capacity if your ambient design temperature is not much more than 90°F. Load calculation is more a good estimate when you don't know the users. In an office it is more predictable by the number of PCs, lights etc. In residential, one day my wife bakes cookies (cooling load), the other day not

 

[meroelme]

What I wanted to know is if: after calculating the cooling load in a space say for example 12MBtu/hr or 1ton, does it mean i have to buy a 1 ton ac unit?

 

[walz]

Power is the rate of doing work....Its units are Watts, kW, BTU/hr ot Tons of ref

AS far as name plate rating is concerned.... its the electrical power. which means the power required for the unit like a 60 W electrical bulb.

When an air conditioning unit is sized and rated lile 2 tons capacity or 5 tons.... this is the thermal power. Its not the electrical power. this means that this unit is capable of prducing 5*12000 of cooling every hour.

Basic principleas of physics are not wrong. Its not 100% efficient. If you see the cooling capacity (thermal power) of this machine ... and divide electrical power by it, You will get more than 1.

Normally DX type units have a range of about 1.8 to 2 kW / Tons. Which means for every ton electrical [power consumed is 1.8 to 2 kW. Now if we express the thermal power One ton also in kW which is 3.51 kW. the ratio becomes

1.8 (electrical power) / (3.51 Thermal Power)= 0.514

Dont mix the two powers... One of them is electrical, other is thermal

 

[meroelme]

Thanks watz, for a clearer explanation regarding the thermal and electrical power.

<b>So, the question now is becoming clearer, if after calculating the space heat load as say for example 1 ton (thermal power) how much factor would you recommend so I could multiply it to the calculated thermal power so I could correctly size my ac unit? Or are there any standards where I could used to properly choose an ac unit after calculating the space heat load?<b>

By the way, all reply are of big help to me...

Thank you so much.

 

[willard3]

Actually, ac units are Carnot cycles with power/heat ratios in the range of 3:1 for very good ones.

 

[EEJaime]

From the electrical side I would reinforce what the other respondents say. Whatever your heat load calculations tell you should be used for your unit sizing. Unit nameplate ratings tell us electrical types what we need to know to properly provide power to run the units. Those ratings while related to the amount of cooling, include many other factors, fan loads, motor efficiencies, control power requirements, ancillary loads, etc.... It would be a big mistake to try to convert that to cooling load capacity.

Regards,
EEJaime

 

[mauricestoker]

You might be looking for the ARI 210/240 rating. The SEER rating would be better for discussing efficeincy for a PTAC or small unit.

 

[meroelme]

Thanks guys for the response, it really helps.

 

[curtis2004]

meroelme,
There is so called the coefficient of performance or COP (sometimes CP), of a AC or heat pump is the ratio of the change in heat at the "output" (the heat reservoir of interest) to the supplied work.
COPcooling = deltaQcold/deltaW

deltaQcold - is the heat moved from the cold reservoir (to the hot reservoir;
deltaW - is the work consumed by AC.
COP (or CP) also can be shown in a nameplate.
Regards,
curtis