Heating water - simple answer hopefully?

[Keith9534]

Hi

 

Hopefully there is a simple scientific answer to my question?

 

I`m trying to work out the most efficient way to run my spa.

 

The water is contained in an insulated plastic enclosure like a paddling pool. There is a top insulated cover. The water is heated by an electric element and pump which circulates the water. The pump/heater can take the water from 16c to 40c in about 5 hours.

 

The whole thing is inside a room which has been designed to maximise solar gain - so much so it recorded 49c as a maximum last year and regularly stays between 38-45c for about 6 hours a day with no mechanical help. There are no drafts in the room and its well insulated and can hold temperature well.

 

Is it beneficial to take the top cover off during the heating cycle while the room temperature is higher than the water temperature?

 

Any help greatly appreciated.

 

 

 

[Externet]

 

Is it beneficial to take the top cover off during the heating cycle while the room temperature is higher than the water temperature?

 

 

 

Yes.

[Acme]

Cross-post: To expand on Externet's succinct reply, heat flow is always from hotter to cooler.

[Keith9534]

Regardless to the mediums where the heat is held? ( doesn`t sound correct but only way to describe it )

 

Would the cooler item eventually reach the same temperature as the hotter item under these circumstances?

[Acme]

Regardless to the mediums where the heat is held? ( doesn`t sound correct but only way to describe it )

 

Would the cooler item eventually reach the same temperature as the hotter item under these circumstances?

Yes, regardless of medium and yes the cooler will reach equilibrium with the hotter. Here's a wiki on heat transfer: >>Heat transfer

[Danijel Gorupec]

"What if" question (for my personal interest):

 

- What if the 'paddling pool' is very white and water is transparent

- and the 'top cover' is black and not very insulating

- and there is direct sunlight

 

Would you still recommend removing the cover? That is, if there is direct sunlight, would you recommend covering the poll with some thin black non-insulating cover?

[Acme]

"What if" question (for my personal interest):

 

- What if the 'paddling pool' is very white and water is transparent

- and the 'top cover' is black and not very insulating

- and there is direct sunlight

 

Would you still recommend removing the cover? That is, if there is direct sunlight, would you recommend covering the poll with some thin black non-insulating cover?

So Keith asked; "Is it beneficial to take the top cover off during the heating cycle while the room temperature is higher than the water temperature?"

 

If you wanted to shorten the heating cycle, i.e. the time the electric water heater runs, then I think the black material should be on the bottom of the pool & not the top while the pool was in direct sunlight.

 

I think experimentation would be the best way to test your setup what with the varying heat conductance by material type and thickness of the cover. Then too, the air gains and loses heat faster than the water so a black top cover -it seems to me- would mostly serve to heat the air.

[John Cuthber]

Hi

 

Hopefully there is a simple scientific answer to my question?

 

I`m trying to work out the most efficient way to run my spa.

 

The water is contained in an insulated plastic enclosure like a paddling pool. There is a top insulated cover. The water is heated by an electric element and pump which circulates the water. The pump/heater can take the water from 16c to 40c in about 5 hours.

 

The whole thing is inside a room which has been designed to maximise solar gain - so much so it recorded 49c as a maximum last year and regularly stays between 38-45c for about 6 hours a day with no mechanical help. There are no drafts in the room and its well insulated and can hold temperature well.

 

Is it beneficial to take the top cover off during the heating cycle while the room temperature is higher than the water temperature?

 

Any help greatly appreciated.

 

 

 

Probably.

But it's possible that evaporative cooling would chill the water faster than the poor conductivity and poor heat capacity of air would heat it.

It depends on the humidity etc.

[Danijel Gorupec]

-it seems to me- would mostly serve to heat the air.

Yes, I also think that maybe such setup would mostly heat the air.

 

I asked this question because OP reminded me of my own dilemma I had some time ago - how to make sun heats water in a shallow pool faster... First idea was, of course, to make the pool interior black. But then I started thinking that maybe water surface is too reflective at certain angles, and thus making a thin non-glossy black foil cover could be a better solution.

 

In any case, I don't know if in OP case there is direct sunlight at all...

[Acme]

Yes, I also think that maybe such setup would mostly heat the air.

 

I asked this question because OP reminded me of my own dilemma I had some time ago - how to make sun heats water in a shallow pool faster... First idea was, of course, to make the pool interior black. But then I started thinking that maybe water surface is too reflective at certain angles, and thus making a thin non-glossy black foil cover could be a better solution.

 

In any case, I don't know if in OP case there is direct sunlight at all...

When Keith said "a room which has been designed to maximize solar gain" I presumed there was direct sunlight.

 

As to your shallow pool and Keith's setup I still think experimentation would deliver the quickest answer(s) given all the complex variables involved.