gadfly56
Senior Member
- Location
- New Jersey
- Occupation
- Professional Engineer, Fire & Life Safety
The OP says this is residential 240VAC; no SQRT(3) here.
AC TONS TO CURRENT
- Thread starter florida-sparkey
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The OP says this is residential 240VAC; no SQRT(3) here.
junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
Note: did not see a couple of previous posts basically saying the same thng as below.
Hmm. 3412 GTUs per kW-hr, resistance heat. IF there were such a thing as resistance cooler, the kW for 48,000 BTU/hr would be 14kW.
So, that converter is converting simple BTUs to kW, no HP COP involved.
Divide by COP of HP to get HP actual kW input. You can calculate the COP from the SEER rating of the HP you are looking at, or lookup the COP fromt he data sheet.
First thought was Lordy, that converter must be based on 1950s 8 SEER HP (as if they had SEER then) with a COP of just over 1 !
My ground source HP runs about 16.5 A putting out 59,500 BTUs/hr (almost 5 T). About 0.85 PF as not an inverter driven unit, so 3.4 kW for 5 Tons. If OP customer has GSHP, 4T kW may be as low as 3 kW.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
He doesn't know the kW yet, that's the stated problem from the outset.
Often times electricians are required to prepare a site for an installation of AC or refrigeration and when we ask for the equipment requirements, the mechanical people respond by telling us the number of tons of cooling capacity they are supplying. Sure we can read it off of the nameplate or data sheet when it arrives, but nobody wants to wait that long to decide what needs to go it, they want the circuit in place ready for connection when it arrives.
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
- Occupation
- Retired
Here in the USA, it is common to use BRITISH thermal units for heating and cooling capacity. A ton (tonne?) is 12,000 BTU, historically the cooling energy in melting a ton (I won't get into which ton, but assume it is our 2000 lb) of ice.
But as others have pointed out, the thermal work is usually (common exception being resistance heat) far more than electrical input. I'm far from an expert, but SEER (seasonal [average]energy efficiency ratio?) over 10 for cooling is routine.
Does UK use kW for both the thermal and electrical energy? I know you, like most of the world, do for electric motors where a 10 kW motor is 10 kW out, and likely 10.3 kW or so in with (in that example) 300 W of waste heat.
Thank you for the polite and considered response.
The kW is a measure power. Energy is kWh.
I know what the BTU is but haven't used it since I was in nappies - diapers in your parlance..........
An imperial ton is 2240 lbs. A tonne or metric tonne as it is sometimes called is 1,000kg so 2,205 pounds. Not often used.
But we are not very consistent. Go in a pub, order drinks. I get a pint of beer, my dear wife gets a 250ml glass of wine. A mish mash. I get 60 mpg fuel consumption from my car but I buy fuel by the litre. And pay for in in pounds sterling. Car engines are routinely rated in horsepower. Tyres (tires) are dimensioned in inches as a rule although I did have a Cologne built Ford that had "metric" tyres.
Ask anyone for their body weight (if you dare) and mostly they will express it in stones and pounds. A stone is 14 pounds. I'm 80kg. So 12 stone 8 lbs.
A right mish mash.............
I don't know how we got there. The pint for beer was a campaign by CAMERA. Campaign for real ale. But if I buy beer in a can it is often 500 ml.
My dear wife cooks brilliantly But, being from across the pond, the recipes are usually in pounds, ounces, and cups. That last one is a conversion challenge.
Enough.
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jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
Because we are Americans and believe that we have a natural born right to do things the hard way.
Fairy 'nuff......................Because we are Americans and believe that we have a natural born right to do things the hard way.
So the air conditioner driver motor capacity must be at least equal to cooling capacity and motor FLA calculated accordingly.
no
the capacity decreases to match input power
for example
at its optimum operating point clg = 14000
very hot day capacity goes to ~ 7000
You mean, on very hot days, a 1 ton air conditioner works as a 1/2 ton air conditioner or even though 2 ton air conditioner works as a 2 ton air conditioner ie extracting the same amount of heat from conditioned space, design inside temperature is not maintained due to outside temperature deviation beyond design limit?
no, they both lose eff/capacity
it's a pump
they only pump 1/2 as much so they must run longer
if rate of gain > removal they can't keep up and space temp rises
the links I posted show capacity vs oat
it goes down and power goes up some
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
A British Thermal Unit is the quantity of heat required to raise the temperature of one pound of water (454 grams) by one degree Fahrenheit. A BTU is close to one kiloJoule and it's an inexact definition, because the thermal capacity of water changes with changing temperature. I enjoy the irony of Americans using the British Thermal Unit, but not the British.... I know what the BTU is but haven't used it since I was in nappies - diapers in your parlance..........
An imperial ton is 2240 lbs. A tonne or metric tonne as it is sometimes called is 1,000kg so 2,205 pounds. Not often used.
But we are not very consistent. Go in a pub, order drinks. I get a pint of beer, my dear wife gets a 250ml glass of wine. A mish mash. I get 60 mpg fuel consumption from my car but I buy fuel by the litre. And pay for in in pounds sterling. Car engines are routinely rated in horsepower. Tyres (tires) are dimensioned in inches as a rule although I did have a Cologne built Ford that had "metric" tyres.
A right mish mash ...
A calorie is a similar unit, the quantity of energy required to raise the temperature of one gram of water by one degree Fahrenheit. But when referring to the energy contained in food, we use the kiloCalorie and call it a calorie.
We have a similar mishmash on this side of the pond. A pint of beer and a pint of milk aren't the same size, but most Americans don't know what a pint is anyway. There are a dozen different definitions of the ton, and they're used to measure mass, weight, force, volume, power and energy. (fortunately, the refrigeration ton is unambiguous, even if few Americans -- even those in the air conditioning trade -- actually know what it is)
Mixed units are commonly used side by side in the same context. Automobile tires here are designated by the width in millimeters and diameter in inches. Bicycle tires use a Byzantine system that I've been unable to decrypt completely, but I have learned that "1¾" is different than "1.75" Air-conditioning engineers often express humidity in grains (1/7000 pound) of water vapor per pound of air.
When people demonstrate that they don't understand the refrigeration ton and casually toss about a phrase such as "4-ton air conditioner", I sometimes jerk their chain, saying they'll need a bigger truck to deliver it and a stronger crew to install it.
And if you live close to the border, as I do, (I live just 15 km north of the Canadian border) it gets even more interesting. The labels on new Canadian cars say they achieve 20% better miles-per-gallon than their seemingly-identical American counterparts. (a great many "American" cars are built in Canada) To further confuse matters, Americans use fuel economy (distance per unit of fuel) and the rest of the world uses fuel consumption (units of fuel per distance)
The nice thing about standards is that there are so many different ones to choose from.
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So the minimum motor power is 2.7 kW. What motor kW is actually given by the manufacture for 2 ton unit?
maximum motor power
good question
looks like 12.9 a at 208/1 no pf given
2.7 kva
so it looks like fla rated at ~ 2 cop or lowest rated eff for a given unit
makes sense, size ckt for worse anticipated case
a heat pump can go to cop = 1 when oat < -10 F or so
pretty sure the motors are sized for mid range but have a sf of ~2
those hi/lo operating conditions are a very small % of the runtime
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Good points. Maybe the Canadians use Imperial gallons for their MPG hence the difference. I believe they tend to use SI from the work I have done there.
And we use miles per (Imperial) gallon here too. Other places use litres per 100km or something such.
I'm quite an old fellow so I grew up with Imperial measures, then CGS, then MKS then SI. I can do most of the common conversions with a bit of mental arithmetic and I have been lumbered with a reasonable memory for conversion factors. Hectares to acres, inches to mm, stuff like that. But probably for at least the last couple of decades work has been all SI.
Superb explanation:thumbsup: May be the AC unit under discussion has a hermetic compressor motor for which there may not be hp/kW rating; only fla rating.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
Right you are. I'm disappointed to admit that it took me a month to figure out what took you a few minutes, but imperial measures are almost never encountered over here.
Canadian cars are labeled in both miles per imperial gallon and liters per hectokilometer. Fuel pumps at filling stations now use liters exclusively, although there's one rather infamous incident from 1983 in which a filling station at the Montreal airport was apparently still calibrated in gallons or pounds. https://en.wikipedia.org/wiki/Gimli_Glider
Mods be kind - know this a bit off topic.
Well, as I said, I'm old going on ancient and grumpy as hell. Or worse........
Slightly more seriously I have travelled much of the world. Including east to west in Canada. Big country.
South Africa before and after apartheid. A roller coaster ride some might say. My dear wife is from GA. I'm a Scotsman living in England. Our dog, a collie, is definitely of Scottish extraction.
Is there a point to this post.......probably not. The previously flying Scotsman. Flying isn't really an option now with our big hairy beast. Doable but I wouldn't wan him
stuck in a crate for a nine hour flight. But he will happily lay in the back seat of the car for a thousand mile jaunt. And he is with us.
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You may rather say you are in the second half of your life meant for new goals to have and achieve,e.g making at least England to adopt SI units in air conditioning field, apart from your goal of long walk with your dog.
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