Do you really need a pump?

[MikeInRialto]

When I took an environmental biology class we did a lab to determine which background color attracted more light for a solar heater. What I now find interesting is that we didn't use pumps and the water temp rose by 10-15 degrees.

Wouldn't a solar heater still heat the pool without a pump if it's a closed system? Obviously it wouldn't move water as fast, but then water being moved should be hated to its maximum potential & you'd be $aving because there is no electrical coast.

Of course you would have to eliminate every last air bubble you could (reverse fill)

*I may be completely wrong - comments?

[J.P.M.]

When I took an environmental biology class we did a lab to determine which background color attracted more light for a solar heater. What I now find interesting is that we didn't use pumps and the water temp rose by 10-15 degrees.

Wouldn't a solar heater still heat the pool without a pump if it's a closed system? Obviously it wouldn't move water as fast, but then water being moved should be hated to its maximum potential & you'd be $aving because there is no electrical coast.

Of course you would have to eliminate every last air bubble you could (reverse fill)

*I may be completely wrong - comments?

Not wrong, but there is a more going on than you are aware of.

Heat transfer 101 - lesson 1 - quality vs. quantity.

Flat plate solar heaters for pool, domestic water, space heating or other applications are most efficient when fluid is circulated through them to keep the panel temps. as low as possible for the application. Things hotter than their surroundings (like stagnant solar panels) lose more heat than cooler things (like solar panels with water running through them). That extra lost heat means less heat is available for the task - in this case, making a relatively larger volume of water (a swimming pool for example) hotter.

There is a difference between quantity of heat and quality of heat. 100 gal. of H2O heated 1 deg. F. and 10 gal. of H2O heated 10 deg. F. require equal amounts of energy. The quantity of heat energy added is the same in either case. However, the 100 gal. heated 1 deg. F. is an easier task because it will happen at a lower temp. and therefore will lose less heat to the surroundings in the heating process. One way to look at it is you want to add the greatest (necessary) quantity of heat while increasing the quality (temp.) of the heat for particular portions of all the water (in this case the water going through the collectors) the least amount consistent with accomplishing the task.

If the task is to increase all the pool water temp. by, say, 10 deg. F. over the course of a day, the more efficient way to do it is to pump more water through the collectors keeping the inlet to outlet temp. difference as small as possible rather than pumping less water through the collectors and thus having a higher inlet to outlet temp. diff. There is only so much energy hitting the collectors. the higher the collector temp., the greater the heat loss. That heat loss becomes unavailable to heat the water. That works against the goal of heating the pool water.

That's the basics. The particulars about tradeoffs in pumping power, dirt, servicing and lots of other details modify the above some, but not enough to change the basics in any meaningful way for a well designed system.

[MikeInRialto]

thank you so much for your reply - but can you dumb it down a bit for me

[inetdog]

thank you so much for your reply - but can you dumb it down a bit for me

The problem is that you not only have to heat the water in the panel, you have to get that hot water back to the pool so that the panel can heat more water.
The lower the temperature of the water in the panel the better it will absorb heat and it will also lose less heat during the trip back to the pool or tank.

[thejq]

The amount of heat energy transfer between two objects is directly proportional to the temperature difference (among other factors like heat conductive coefficient etc.). In other words, the bigger the difference the faster the heat transfer. The sun light heats the solar collector and raises its temperature. When water is passed through it, the temperature difference allows energy to be transferred from the collector to the water. If water is not moving, it's temperature will rise and eventually equate that of the collector hence no energy is transferred. Moreover with stale water, the collector's temperature will also rise significantly hence creating a temperature differential to the surrounding air, hence energy will be lost to the air. One also has to know water circulation is require with or without solar heating to keep the pool water filtered and clean.

Perhaps when you did your project, you painted the the entire water container black, so there's no need to circulate the water. But in residential application, I don't think anyone wants to paint the entire pool black or brown just to absorb more solar energy or not having to circulate the water.

[J.P.M.]

The amount of heat energy transfer between two objects is directly proportional to the temperature difference (among other factors like heat conductive coefficient etc.). In other words, the bigger the difference the faster the heat transfer. The sun light heats the solar collector and raises its temperature. When water is passed through it, the temperature difference allows energy to be transferred from the collector to the water. If water is not moving, it's temperature will rise and eventually equate that of the collector hence no energy is transferred. Moreover with stale water, the collector's temperature will also rise significantly hence creating a temperature differential to the surrounding air, hence energy will be lost to the air. One also has to know water circulation is require with or without solar heating to keep the pool water filtered and clean.

Perhaps when you did your project, you painted the the entire water container black, so there's no need to circulate the water. But in residential application, I don't think anyone wants to paint the entire pool black or brown just to absorb more solar energy or not having to circulate the water.

The directly proportional part of your statement is true for conduction heat transfer (no fluid circulation), and to some complicated degree for convective heat transfer (the case of water circulating through a flat plate collector for example), but incorrect for radiant heat transfer (solar energy heating an object).

FWIW, for residential pool heating, I had a pool cover that was very dark brown. I kept it in place when the pool was not in use. It kept the pool temp. above 85 F. from mid April to mid Oct. in Albuquerque.