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Thermal Problem
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Jim Thompson
electronics forum Guru


Joined: 06 May 2005
Posts: 5440

PostPosted: Fri Jul 21, 2006 2:20 am    Post subject: Thermal Problem Reply with quote

Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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Michael A. Terrell
electronics forum Guru


Joined: 24 Mar 2005
Posts: 2291

PostPosted: Fri Jul 21, 2006 2:35 am    Post subject: Re: Thermal Problem Reply with quote

Jim Thompson wrote:
Quote:

Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

...Jim Thompson


Find a place that repairs resteraunt equipment and get the chiller
from an orange juice or milk dispenser. Lots of machines get scrapped
but they still have a good compressor and heat exchanger. The place I
knew about moved, and I lost track of them, but they had over 100 spare
chillers in their warehouse the last time I talked to them.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
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Luhan
electronics forum Guru


Joined: 10 Dec 2005
Posts: 365

PostPosted: Fri Jul 21, 2006 2:40 am    Post subject: Re: Thermal Problem Reply with quote

Jim Thompson wrote:
Quote:
Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

Is the raised temperature caused by the lighting or is there another
heat source?

Maybe some light source with less IR? Or do you need it for the
plants?

Luhan
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Fri Jul 21, 2006 2:52 am    Post subject: Re: Thermal Problem Reply with quote

Jim Thompson wrote:
Quote:
Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

If the tank is hotter than room temperature, something has to be
heating it - probably your lights. If you work out the wattage of all
the lamps that you have got feeding visible and infra-red radiation
into the tank, you'll probably get a reasonable idea of how much heat
your chiller has to take out.

If you've got a circulating pump, the power that it dissipates is
probably ending up in the tank as well, so add that in too.

You might save some money by illuminating your tank with efficient
light sources - straignt or folded fluorescent tubes.

Incidentally the latent heat of evaporation of water is 2.26E6 joules
per kilogram, and the latent heat of melting for ice is 3.33E5 joules
per kilogram. The heat capacity of water is 4186 joules per kg. The
American gallon is 8 lbs of water, or 3.632 kg.

Your two gallons of ice took 2,42E6 joules to melt, and should have
cooled your tank by 0.66C or 1.2F. You need a better thermometer.

--
Bill Sloman, Nijmegen
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Jim Thompson
electronics forum Guru


Joined: 06 May 2005
Posts: 5440

PostPosted: Fri Jul 21, 2006 3:03 am    Post subject: Re: Thermal Problem Reply with quote

On 20 Jul 2006 19:40:36 -0700, "Luhan" <luhanis@yahoo.com> wrote:

Quote:
Jim Thompson wrote:
Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

...Jim Thompson

Is the raised temperature caused by the lighting or is there another
heat source?

Maybe some light source with less IR? Or do you need it for the
plants?

Luhan

It's a reef tank, the lighting is needed for the coral.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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gfretwell@aol.com
electronics forum addict


Joined: 10 Nov 2005
Posts: 90

PostPosted: Fri Jul 21, 2006 3:28 am    Post subject: Re: Thermal Problem Reply with quote

On Thu, 20 Jul 2006 19:20:54 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote:

Quote:
Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

...Jim Thompson

Maybe you just need to put a big coil of hose in your pump line so it
can heat exchange with the cooler room air.
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The Phantom
electronics forum Guru Wannabe


Joined: 05 May 2005
Posts: 186

PostPosted: Fri Jul 21, 2006 4:17 am    Post subject: Re: Thermal Problem Reply with quote

On Thu, 20 Jul 2006 19:20:54 -0700, Jim Thompson
<To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote:

Quote:
Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

...Jim Thompson

Every gram of ice at 32 that melts absorbs 80 calories as it becomes
water at 32, which will lower the temperature of 1 gram of water 80.
Since it's all proportional, that means (all this is approximate, of
course) that 2 gallons of ice at 32 upon melting will lower the
temperature of 2 gallons of water 80; it will lower the temperature of 20
gallons of water 8, and it will lower the temperature of 200 gallons of
water .8--you get the picture. If the ice is at a temperature lower than
32 to start, then there will be a little additional cooling as the
temperature of the ice comes up to 32 and melts. But, most of the cooling
is from the change of phase of the ice.
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Brian
electronics forum Guru


Joined: 02 May 2005
Posts: 323

PostPosted: Fri Jul 21, 2006 4:31 am    Post subject: Re: Thermal Problem Reply with quote

<bill.sloman@ieee.org> wrote in message
news:1153450323.978444.230300@i3g2000cwc.googlegroups.com...
Jim Thompson wrote:
Quote:
Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

If the tank is hotter than room temperature, something has to be
heating it - probably your lights. If you work out the wattage of all
the lamps that you have got feeding visible and infra-red radiation
into the tank, you'll probably get a reasonable idea of how much heat
your chiller has to take out.

If you've got a circulating pump, the power that it dissipates is
probably ending up in the tank as well, so add that in too.

You might save some money by illuminating your tank with efficient
light sources - straignt or folded fluorescent tubes.

Incidentally the latent heat of evaporation of water is 2.26E6 joules
per kilogram, and the latent heat of melting for ice is 3.33E5 joules
per kilogram. The heat capacity of water is 4186 joules per kg. The
American gallon is 8 lbs of water, or 3.632 kg.

Your two gallons of ice took 2,42E6 joules to melt, and should have
cooled your tank by 0.66C or 1.2F. You need a better thermometer.

--
Bill Sloman, Nijmegen


Pssst, Bill, you missed the fact that the heat source was STILL present,
significantly reducing the 1.2F drop (balanced with heat loss to the outside
world) and making it negligible in the full equation of all sources of
heating and cooling. Not a "static" environment.
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Paul Hovnanian P.E.
electronics forum Guru


Joined: 29 Apr 2005
Posts: 583

PostPosted: Fri Jul 21, 2006 5:38 am    Post subject: Re: Thermal Problem Reply with quote

Jim Thompson wrote:
Quote:

Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

What is the total rating of the heat input? Lighting, pumps, etc.
That'll be a starting point to sizing your chiller.

Next thing: What is the humidity of the environment where the tank is?
If your AC keeps the area pretty dry, you are still going to lose some
water even if you cool the tank down.

--
Paul Hovnanian mailto:Paul@Hovnanian.com
------------------------------------------------------------------
100 buckets of bits on the bus
100 buckets of bits
You take one down,
and short it to ground
FF buckets of bits on the bus
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Jeff L
electronics forum beginner


Joined: 04 Sep 2005
Posts: 47

PostPosted: Fri Jul 21, 2006 8:46 am    Post subject: Re: Thermal Problem Reply with quote

<gfretwell@aol.com> wrote in message
news:7ci0c2tt6rej0dg7hl3nd52c877t438kf9@4ax.com...
Quote:
On Thu, 20 Jul 2006 19:20:54 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon@My-Web-Site.com> wrote:

Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Acrylic is a fairly good thermal insulator,

Most of the heat loss is from evaporation, conduction / convection, and some
radiant heat. I would think that it would be reasonable to assume that the
heat loss from convection /conduction from the surface of the water would be
more then the heat loss through the acrylic. Also, how is the pump and
filter setup done - can significant heat escape there? Unfortunately the
only easy calculation is for evaporation. Another problem is the conduction
/ convection heat losses will disappear once the temperature differential
disappears.

The easiest way to calculate the needed cooling is to figure out what the
heat generation rate is for the aquarium.

Most of your heat is from lights, IR heat (sun?), the pumps mechanical work
and possibly motor cooling. Some small amounts of heat may come from the
fish and other bio heat.

What is the wattage and type of lighting? Qty of lights?
What is the pump wattage, and how is the motor cooled?
Does the sun shine on it?
How much *food* energy is dumped in the aquarium a day?


Your tank has a thermal storage of:
Size of tank = 243.8 cm x 60. 96 cm x 60.96 cm = 906 L water => ~906 kg
water
specific heat of water = 4.182 kj/kg K @ 25 deg C
which gives: 3,788 kj / K

Assuming the 3% or so change in density from pure to salt water, the thermal
storage of the tank, and the less then full tank sum to a neglectable
amount.



Quote:

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

This removes about:
Loss of water = ~ 7.5 L a day -> which is about 0.31 L (kg) per hour
Latent heat of fusion of water = 2260kj / kg
Which gives a cooling rate of about 712 kj per hour, assuming a constant
rate

Note, this cooling effect will decrease as the temp differential decreases.


Quote:

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

No good - that's like specking a air conditioner on house square footage.

Quote:

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

This would possible be equivalent to 1 gallon of ice due to the air content.

Lets assume 4 kg of ice:
Latent heat of fusion of water = 333kj / kg
This therefore removed about 1332 kj of heat. Considering the thermal mass
of the tank is 3,788 kj / K, the temp would have dropped by about 0.35 deg C

Quote:

...Jim Thompson

Maybe you just need to put a big coil of hose in your pump line so it
can heat exchange with the cooler room air.

I like this solution, however a coil won't likely do it, as several kj of
heat need to be removed an hour at an almost zero temp differential. A
liquid to air heat exchanger would be more ideal (think small radiator).
Temp could be controlled by a diverter valve and / or fan, or just use the
ambient air temp to keep things inline. Circulating cool water through a
liquid to liquid heat exchanger would also work. Jim, what's your cold water
source like (cheap, cold - if so, what temp?)? Due to the salt water, the
heat exchangers would likely have to be stainless steel.

A reasonable guestimate would be that you need to remove about 2000 to 3000
kj per hour, and considering that a BTU is 1.055 kj, a 2000 to 3000 (which
is a 1/4 ton unit!) BTU chiller would do if that guestimate is correct. If
you want faster cooling and more compressor cycling, which reduces
efficiency somewhat, a larger unit could be used.

Also putting lot's of bubbling air ornaments in the water will help cool it,
mostly by aiding in substantial evaporation.
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Bill Sloman
electronics forum Guru


Joined: 12 May 2005
Posts: 1080

PostPosted: Fri Jul 21, 2006 10:40 am    Post subject: Re: Thermal Problem Reply with quote

Brian wrote:
Quote:
bill.sloman@ieee.org> wrote in message
news:1153450323.978444.230300@i3g2000cwc.googlegroups.com...
Jim Thompson wrote:

<snip>

Quote:
Pssst, Bill, you missed the fact that the heat source was STILL present,
significantly reducing the 1.2F drop (balanced with heat loss to the outside
world) and making it negligible in the full equation of all sources of
heating and cooling. Not a "static" environment.

You haven't worked with thermostatted baths, have you - two gallons of
cracked ice fed into a pumped system looks very like a Heavyside
impulse.

240 US gallons of water is 3.65E6 joules/degree C of heat capacity.
Jim's tank is 5C hotter than ambient, and let us say he has about 100W
worth of lighting, so the thermal resistance from tank to ambient is
0.05C/W, then the thermal time constant of the tank would be about 50
hours. That seems a bit long - my very well insulated hot water tank in
Cambridge, which held the same sort of volume of water, had that sort
of time constant, so Jim has probably got bigger lights than the number
I first thought of.

In any event, the ice will melt a lot faster than the lamps could have
melted it.

If you can measure temperature accurately, at reasonalby regular
intervals over something like one thermal time constant, you can ensure
the thermal resistance to ambient surprisingly accurately - I've
mesured a thermal time constant to +/-0.5% on at least one occasion.

--
Bill Sloman, Nijmegen
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Chuck Harris
electronics forum Guru


Joined: 03 May 2005
Posts: 326

PostPosted: Fri Jul 21, 2006 12:00 pm    Post subject: Re: Thermal Problem Reply with quote

Jim Thompson wrote:
Quote:
Salt Water (Reef) Aquarium Tank...

8' X 2' X 2' Acrylic-walled (3/4") tank (~240 Gallons)

Covered on top by actinic and visual-white lighting, but with vents

Evaporation rate ~2 Gallons/day

Room temperature 76F

Tank temperature 85F

Desired tank temperature 76-78F

How much cooling (chiller) is required?

Not easy... the shops only specify a chiller size versus tank gallons.

I put 2 gallons of chipped ice (R/O) into the sump... no discernable
change of temperature.

...Jim Thompson

1 BTU will lower(raise) 1 pound of water 1 degree F.
1 gallon of water weighs 8 pounds.

You need to lower 240 gallons, 1920 pounds of water 9 degrees F.
That takes 17280 BTU in a perfect no heat gain/loss system.

All you need to figure out is how quickly you want to make the
temperature change. That is where the insulation factors of the
acrylic, and the room air temperature come into play.

You can experimentally determine the heat gain by heating the tank to
1 degree above room temperature, and timing how long it takes
to drop back down to room temperature. That will be the number of
hours the system needs to lose 1920 BTU.

-Chuck
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