Chiller Sizing Gurus Please Read

[mojo]

grouper therapy;620460 wrote: If that were the case a 20 hp/ton would only use 80 watts. It is not a linear equation.

No... but to Raj's point, it would use less that same 4840 watts for much less time. How much would depend on too many factors to calculate.


For what it's worth, I run a 2hp JBJ chiller on my 680-800g system (varies depending on if my frag tank is online), and it seems to be about right, based on the on/off times during the summer months.

 

[morganatlanta]

What exactly are chillers measuring when the give a horse power rating? Is that the rate it can pull heat out of the water?

 

[rbredding]

mojo;620545 wrote: No... but to Raj's point, it would use less that same 4840 watts for much less time. How much would depend on too many factors to calculate.


For what it's worth, I run a 2hp JBJ chiller on my 680-800g system (varies depending on if my frag tank is online), and it seems to be about right, based on the on/off times during the summer months.

how long does it take to cycle ?

from off, to on, to off ? (I assume your controller brings the temp down 3-4 degrees?)

Edit:

MorganAtlanta;620564 wrote: What exactly are chillers measuring when the give a horse power rating? Is that the rate it can pull heat out of the water?

no, it's the power of the compressor motor..

 

[mojo]

MorganAtlanta;620564 wrote: What exactly are chillers measuring when the give a horse power rating? Is that the rate it can pull heat out of the water?

Horsepower and BTU's are both measurements of power (well, technically one is energy and one is power, since once is a measurement that includes time).

1 horsepower equals 42.44 BTU/min, or roughly about 2,500 BTU's/hr. A BTU is a British Thermal Unit - the amount of heat added or removed from the system.

For the sake of our aquariums, yes, "horsepower" equates to the amount of heat that it can remove over a given amount of time. Bigger systems need more horsepower because they produce more heat.

Edit:

Rbredding;620565 wrote: how long does it take to cycle ?

from off, to on, to off ? (I assume your controller brings the temp down 3-4 degrees?).

In the dead of summer, it'll stay on for about 10-15 mins and off for about 20-30 mins for a 2 degree pulldown. I've never actually timed it to any great accuracy, but when my apex used to work, I could watch the chiller times based on the temperature graph.

 

[grouper therapy]

mojo;620545 wrote: No... but to Raj's point, it would use less that same 4840 watts for much less time. How much would depend on too many factors to calculate.
Not necessarily. Especially if the flow rate through the exchanger is not at the most efficient rate for heat exchange. You could be running a 2hp chiller at a rate that doesn't allow enough contact time for maximum heat transfer.

For what it's worth, I run a 2hp JBJ chiller on my 680-800g system (varies depending on if my frag tank is online), and it seems to be about right, based on the on/off times during the summer months.

Have you calculated your power consumption?

 

[grouper therapy]

mojo;620567 wrote: Horsepower and BTU's are both measurements of power (well, technically one is energy and one is power, since once is a measurement that includes time).

1 horsepower equals 42.44 BTU/min, or roughly about 2,500 BTU's/hr. A BTU is a British Thermal Unit - the amount of heat added or removed from the system.

For the sake of our aquariums, yes, "horsepower" equates to the amount of heat that it can remove over a given amount of time. Bigger systems need more horsepower because they produce more heat.

Edit:

In the dead of summer, it'll stay on for about 10-15 mins and off for about 20-30 mins for a 2 degree pulldown. I've never actually timed it to any great accuracy, but when my apex used to work, I could watch the chiller times based on the temperature graph.

That is a pull down from the last cycle I assume. What does the tank run with no chiller at all?

 

[skriz]

grouper therapy;620460 wrote: If that were the case a 20 hp/ton would only use 80 watts. It is not a linear equation.

Edit: Too that would be assuming the same rate of flow through the heat exchanger which would change the heat exchange rate as well.

Yeah, I didn't mean it literally. BUT, if it only needs to run for 10 minutes, then it's only going to consume x amount of power.

Nonetheless, I think we all agree that Dave should be fine with a 2 hp chiller!

 

[acroholic]

Guys,
Thank you very much for all the input. I won't pretend to understand all the techinical, formula stuff, hehehe!

One thing I have seen from reading the BTU ratings of a bunch of different chiller brands, is that there seems to be a general level of one HP equals 12000 BTUs. Most 1/2 HP chillers are 6000 BTUs, etc.

 

[rbredding]

yes... remember, those BTU's are "heat units PULLED OUT of the water"... exactly the opposite of BTU numbers on heating devices.

(I know it sounds obvious, but it takes a great deal more energy to pull heat out of the water than it does to put heat into the water)..

Edit:

mojo;620567 wrote: In the dead of summer, it'll stay on for about 10-15 mins and off for about 20-30 mins for a 2 degree pulldown. I've never actually timed it to any great accuracy, but when my apex used to work, I could watch the chiller times based on the temperature graph.

I did the same thing.. I'd plot temperature vs. amperage to get the complete picture..

 

[mojo]

grouper therapy;620582 wrote: Have you calculated your power consumption?

Total is around $120-180/mo, but I haven't broken it down enough to know what the chiller is using specifically. I've thought about putting a meter on it, but ignorance is bliss...

grouper therapy;620589 wrote: That is a pull down from the last cycle I assume. What does the tank run with no chiller at all?

Yes- that's pull down from the last cycle- sorry if I implied anything else. No idea what it'd run otherwise - I'd guess 10-15 degrees higher than it should, but there's no point in killing the corals to find out.

Acroholic;620624 wrote:
One thing I have seen from reading the BTU ratings of a bunch of different chiller brands, is that there seems to be a general level of one HP equals 12000 BTUs. Most 1/2 HP chillers are 6000 BTUs, etc.

What's interesting is that I came to the same conclusion a while back. But when I typed that in above, I decided to google to find out the specifics. The numbers above reflect those google'd results, but I'm with you - if you look at the manuf's specs, 1 hp chiller == 12,000 BTU's.

I have no idea where the discrepancy is... Can anyone enlighten me?

Edit:

Rbredding;620635 wrote: I did the same thing.. I'd plot temperature vs. amperage to get the complete picture..

My chiller is 220v, so I can't run it through the APEX and get current reading over time. I've got a clamp on current gauge, but I'm too lazy to sit there and write down numbers over time...

 

[morganatlanta]

Rbredding;620635 wrote: yes... remember, those BTU's are "heat units PULLED OUT of the water"... exactly the opposite of BTU numbers on heating devices.

(I know it sounds obvious, but it takes a great deal more energy to pull heat out of the water than it does to put heat into the water)..

Edit:

I did the same thing.. I'd plot temperature vs. amperage to get the complete picture..

That's where I get a bit confused. BTUs are a total amount of energy, where as watts are a rate of energy (energy/time). So saying a heater is 500 watts, makes sense. You know how fast it is adding energy. But saying a chiller is "6000 BTUs", doesn't make sense to me, since any chiller will eventually remove 6000 BTUs of total energy. Is there some sort of "time" and duty cycle implied in that number? (like it is really 6000 BTUs/hr assuming a 10% duty cycle?)

 

[grouper therapy]

Most all btu ratings are per hour.