Comment

Comment by Jacques L. on January 23, 2013 at 11:33am

@John

I concur, as soon as my tanks temps hit 60+ (was 66 last night) those little buggers went to town. Like having Pirahna versus Talapia 

Had put in a few more plants over the past weekend to replace the frost bitten ones that didn't make it.

Heat inside the hoop during the day is positively sunny, can definitely feel the difference in humidity as well. Got a small issue with mosquitoes now. Thinking of putting up some flypaper to keep the numbers down.

Finished up one endframe of the hoop by securing the film, got the other this weekend. It took a bit longer than expected due to the PVC piping coming out that end of the greenhouse. 

Three more days of awesome temps.. hoping to see 70 degrees in the tank by weeks end *fingers crossed* :)

Comment by Dr. George B. Brooks, Jr. on January 22, 2013 at 5:41pm

I see. Facinating. I must learn more of what you speak. You seem to refer to concepts a little different from what I am familiar. In the mean time, here is a link to the abstract of a paper that provides the foundation of my question. Its admittedly a little old, but subsequent research seemed to support it. Don't worry about purchasing it, I'll get a copy from the ASU Science library and post it for your review shortly. I look forward to your comments then and how it compares with your technique. Always new things to learn it seems:

http://www.sciencedirect.com/science/article/pii/0167582681900231 

Comment by Robert Rowe on January 22, 2013 at 4:58pm

@Dr George B. Brooks Jr

Re:

Comment by Dr. George B. Brooks, Jr. 3 hours ago

Just wondering but in your equations have you considered factors that directly affect heat loss or gain? In this case for heat loss, heat lost to evaporation, thermal exhange with the air and night sky radiation? 

If you were referring to my comments, The heat loss in the case of the frost blanket covering is counter intuitive. Where you would think the warm water would be on the surface, however in this case due to the thermal mass, the warm water is at the bottom resulting in less loss due to evaporation and radiation is a questionable topic.

. 

Comment by John Malone on January 22, 2013 at 1:24pm

All gone!

The fish food that's been sitting at the bottom of the tank for the last several weeks, that is.    

The water temp was 63F last night, and the fish food debris was noticeably less than it has been.  This morning at 7am, with water temp still at 60F, I thought it might be worth having a look to see if the food waste was lessening.   Gone.  All of it!   Some little fishies got the munchies once the temp got above 60F, it would seem.

I know it's 'good practice' to remove excess food, but I've never had a problem and my tested water quality is great, so excess food is a great indication that I'm overfeeding.  They don't get any more until the excess is gone.  These tilapia are sensational at cleaning up the mess when they get hungry.

Looks like they get some fresh food today.

Comment by Dr. George B. Brooks, Jr. on January 22, 2013 at 1:07pm

Just wondering but in your equations have you considered factors that directly affect heat loss or gain? In this case for heat loss, heat lost to evaporation, thermal exhange with the air and night sky radiation? 

Comment by Robert Rowe on January 21, 2013 at 3:10pm

@Bob Campbell2013-01-11%20N-Sulate%20-%20Frost%20Protection%20Blanket.pdf

Comment by Robert Rowe on January 21, 2013 at 9:25am

 

@All

Re. my rantings on controlling water temperature. To clarify my comments:

Thermal mass is a concept in building design that describes how the mass of the building provides "inertia" against temperature fluctuations, sometimes known as the thermal flywheel effect.[1] For example, when outside temperatures are fluctuating throughout the day, a large thermal mass within the insulated portion of a house can serve to "flatten out" the daily temperature fluctuations, since the thermal mass will absorb thermal energy when the surroundings are higher in temperature than the mass, and give thermal energy back when the surroundings are cooler, without reaching thermal equilibrium. This is distinct from a material's insulative value, which reduces a building's thermal conductivity, allowing it to be heated or cooled relatively separate from the outside, or even just retain the occupants' thermal energy longer.

Scientifically, thermal mass is equivalent to thermal capacitance or heat capacity, the ability of a body to store thermal energy. It is typically referred to by the symbol C_th and measured in units of J/°C or J/K (which are equivalent). Thermal mass may also be used for bodies of water, machines or machine parts, living things, or any other structure or body in engineering or biology. In those contexts, the term "heat capacity" is typically used instead.

Geothermal Gradient

There exists a point below the surface of the ground at which temperature level remains unchanged over any 24 hour period.

Likewise for a 365 day period.The actual depth is only important to understand the "geothermal gradient" and its influence on heat loss or gain.For the purpose of maintaining a constant temperature, in for example a fish pond, or container sitting on the ground. The ground can be considered as at a relatively unchanging temperature when determining factors influencing the water temperature.

The surface of the water is to be dealt with outside of this discussion.

Application

Given that water weighs 62.5 lb. Per cubic ft.

Sand weighs 100.00 Lb. per cubic ft.

Using a container 4' x 4' x 1' would contain 16 cubic ft of water, weighing 1000 lb.

If I surround this container with 1 foot of sand which would be 20 cubic ft.weighing 2000 lb.

The total mass of the tank is three times as great 3000 lb.

And the thermal change delay would be much improved as well.

 

Comment by Bob Campbell on January 21, 2013 at 8:37am

@Robert Rowe - What is an anti frost cloth?

Comment by Bob Campbell on January 20, 2013 at 11:04pm

@Robert Rowe - I'm sure sand around the tank will help. 

When I read your article about thermal mass I got the impression you are equating thermal mass with mass. 

Sand is heavier than water, but water has a greater thermal mass. 

Comment by John Malone on January 20, 2013 at 5:14pm

Ahhhh - that's better.
After a nice stretch of lovely 70s weather the fish tank water temperature is up to 62F.
Very nice, and fish are all sorts of wriggly and swimming. They're still not eating much, but I font expect that to change until about 70F.

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