relationship between tons of cooling and kW

[mshields]

I'm looking at a Filtrine water cooled chiller with Cooling Capacity of 265,000 BTU/Hr's and looking to find the electrical load.

The FLA is 75A. Ok - so 75A x 480 x 1.73 gives 62kW.

But here's what's concerning me. 265,000 divided by 12000 gives tons of 22

Shouldn't Ton's be approximately equal to kW for a water cooled chiller system?

What am I missing?

 

[MAC702]

Assuming TR is "Tons Refrigeration," that doesn't appear to be the case. But I don't do these, so I'm guessing.

http://www.york.com/for-your-workplace/chilled-water-systems/water-cooled-chillers

 

[electrofelon]

I think your figures are off. Figure 2 kw per ton for MCA, with actual kw about 2/3 of that.

 

[Besoeker3]

I'm looking at a Filtrine water cooled chiller with Cooling Capacity of 265,000 BTU/Hr's and looking to find the electrical load.

The FLA is 75A. Ok - so 75A x 480 x 1.73 gives 62kW.

But here's what's concerning me. 265,000 divided by 12000 gives tons of 22

Shouldn't Ton's be approximately equal to kW for a water cooled chiller system?

What am I missing?

265,000 BTU/hr is about 78kW

 

[charlie b]

If you want a unit conversion factor, then take BTU/HR and multiply by .2931 to get KW. That was Besoeker3's comment.

But this is not a "unit conversion" application. It is not a situation in which energy is converted from one form to another (e.g., electrical to kinetic in an electric car), or one in which energy is used to change the temperature of a substance (e.g., water being heated in a pot on a stove). Yes, the chiller is changing the temperature of the room. But what it is really doing is moving the heat from one location (the room) to a different location (the outside world). So there is no direct "unit conversion" that will take you from the amount of electricity needed to run the machine (i.e., the compressor and fan motors) to the amount of heat the machine can relocate.

 

[electrofelon]

265,000 BTU/hr is about 78kW

This a refrigeration cycle that is moving heat. A theoretical conversion is meaningless.

 

[zbang]

Manufacturers get really loose with their units. I've seen equipment where the wattage rating is not even close to the specified heat dissipation (nor the "cooling tons required").

265,000 BTU/hr is about 78kW

People dropping the hour part, 265k BTU = 77.7 KWH. (BTW is a unit if energy, Watt is a unit of power.)

 

[Besoeker3]

Watt is a unit of power.)

I never would have guessed......:lol:

 

[junkhound]

I'm looking at a Filtrine water cooled chiller with Cooling Capacity of 265,000 BTU/Hr's and looking to find the electrical load.

The FLA is 75A. Ok - so 75A x 480 x 1.73 gives 62kW.

But here's what's concerning me. 265,000 divided by 12000 gives tons of 22

Shouldn't Ton's be approximately equal to kW for a water cooled chiller system?

What am I missing?

You are missing 2 major factors.
a. Power factor
b. If a heat pump chiller; COP -Coefficient of performance of vapor cycle thermodynamic equations. SEER = 'approximately' COP x 3.422

 

[junkhound]

PS: Run numbers and FLA for 480 V is about 25A, perhaps mshields misread 25 as 75?

 

[Jraef]

This problem has vexed ECs for years. The HVAC people give you a value in tons or BTU/Hr and ask us to size the equipment from that, for which there is no good answer. A long time ago I found the following formula and it has checked out fairly closely with what I see in the field, erring on the high side, which means I don't end up not having enough power available in the circuit..

1 BTU/H requires 0.00039 Mechanical horsepower

Mechanical HP is what the machine will need at the shaft. Electrical HP then is mechanical HP plus any electrical losses in creating it, aka motor "efficiency", I usually use 80%, which becomes another "fudge factor".

So your 265,000 BTU/H chiller would come out to 104 mechanical HP (which by the way is 78 kW) or 130 electrical HP, but I'd likely settle on a 125HP motor size and use that for sizing the circuit components.

 

[drcampbell]

This problem has vexed ECs for years. ...
1 BTU/hour requires 0.00039 mechanical horsepower ...

As I've seen somewhere nearby, "You can't generalize". The amount of mechanical (or electrical) power required to extract a given amount of thermal power depends on a myriad of variables in both system design and operating condition. For example: If you don't need to (or choose not to) do humidity control, you can raise the evaporator temperature, which will raise the efficiency, which will reduce the amount of input power needed.

... Watt is a unit of power.

So is a refrigeration ton. (in strict adherence with The Principle of Maximum Confusion, multiple different measurement units are used to measure the same phenomenon.)

 

[electrofelon]

As I've seen somewhere nearby, "You can't generalize". The amount of mechanical (or electrical) power required to extract a given amount of thermal power depends on a myriad of variables in both system design and operating condition. For example: If you don't need to (or choose not to) do humidity control, you can raise the evaporator temperature, which will raise the efficiency, which will reduce the amount of input power needed.


So is a refrigeration ton. (in strict adherence with The Principle of Maximum Confusion, multiple different measurement units are used to measure the same phenomenon.)

That might be in my signature . Which note is actually a fallacy because that statement generalizes.

Fwiw as I mentioned that 2kw /ton for MCA, 1.2-1.4 keep/ ton actual draw should be very close for package HVAC units. I don't have any experience with chillers, but imagine it's not drastically different.

 

[junkhound]

12k/3412 = 3.51

Thus for COP of 3.5 (a decent COP for a chiller), 1 kW per ton

Modern efficient chiller from say a 55F artesian water source to 35F can get COP of over 5 so 700 W/ton

Inefficient chiller from olden day with COP of only 2, 1.75 kW per ton.

OP used a 1 kW/ton assumption which is reasonable, hence the OP number of 75A FLA for 3 phase 480V is erroneous.

 

[topgone]

FACTS:

1. 1 kWh = 3412.142 BTU
2. 1 ton of refrigeration = 12,000 BTU/h

Therefore, 1 ton of refrigeration = 3.51685 kW!

Taking your numbers, (265,000/12,000) X 3.51685 = 77.662 kW

Hope that helps.

 

[Besoeker3]

1 BTU/H requires 0.00039 Mechanical horsepower

Power is power. Whether you express it in HP or kW it is still power.

 

[Sahib]

FACTS:
1 ton of refrigeration = 3.51685 kW!


.

That includes both heat per second extracted from space being cooled and work done per second by the refrigeration compression motor! The OP wants only the latter part, which is nearly equal to 1 kW/ton!

 

[drcampbell]

The Principle of Maximum Confusion, writ large.

Although there are two different units (kW and Ton) being used to measure the same phenomenon (power),
the fundamental confusion arises from measuring two different things:

[1] input power (electrical), and
[2] output power (thermal),
between which there is no direct correlation. The ratio between the two is the machine's efficiency, which varies from machine to machine and installation to installation.

 

[Sahib]

An air conditioner not only removes heat from conditioned space and discharges into atmosphere through condenser, but also does so for the heat of compression of the refrigerant by the compressor motor. If the efficiency is calculated by the ratio of heat discharge through condenser to the energy input in thermal unit to the compressor motor, it will be found it is greater than unity.

 

[Jraef]

Power is power. Whether you express it in HP or kW it is still power.

Well yes, but in converting electrical energy to mechanical energy there are losses. So if you want to know the ABSORBED power in an electrical circuit based upon a known MECHANICAL power requirement, you must factor in the efficiency of the motor. You know that...