Thinking of using a swiming pool as a heat sink

Big Will

I have a building that uses a two pipe system to heat and cool seventy five apartments with small fan coils. Every day in the summer it stops heating at 68 deg outdoor and starts cooling at 73 deg. When it goes to cooling the water is still around 130 deg. It takes the chiller a bit over an hour to bring it down to the operating temp of 48deg. The energy consumption is huge during this change over period. So I did some calculations. The swimming pool is big enough that it could absorb 480,000 BTU and only warm up 1.7 deg. I am thinking the simplest control would be to run a three way valve diverting the water through a pair of large heat exchangers for an hour before letting the chiller come on. A simple high limit control on the pool water temp would keep it from over heating the pool. I know the pool heater runs throughout the summer and this would reduce its run time and the chillers run time. The other part is it sounds like fun. Thoughts.

Big Will

and what about the heat

I could also have the pool bring the water temp back up when the day cools. this would negate the pool heating. However if I could dump the heat into the pool and take it out again later in the day that would be great. A bit more complicated but even more fun. I think it could save some real money. The system has about 600 gallons in it so the thermal mass makes the change over a big deal.

Jean-David Beyer

Big building with pools for heat sinking.

I used to work in this building:



www.preservationnation.org/resources/case-studies/modernism-recent-past/bell-labs.html



It is larger than the one you are talking about, I imagine. The front of the building is near the top of the picture. The two D-shaped dark zones are ponds that are used as heat sinks for the air conditioning system. I do not know the temperature the water gets to, but on very hot days (in New Jersey) thay had to run spray units, not unlike the fountains at Versailles, to get enough evaporative cooling to keep the temperatures down.



http://entertainment.webshots.com/photo/1237034397013919800WdMjJT



The building is actually 4 buildings, each 6 stories high, enclosed in a large glass (originally, now plastic) box. It is about 2 million square feet. Only rarely in winter did the ponds freeze. We produced a lot of heat in there. We had three IBM 360/65 computers and uncounted minicomputers, all putting out heat. Also we had electric furnaces used to make semiconductor devices (for research and development purpose, not manufacturing in quantity.



In fact, when Nixon had a regulation to keep buildings down to 67F in winter, or whatever it was, we had to get a dispensation because It would require our running air conditionign all year around, using more energy than if we let it drift up to about 73F.

Brad White

Ideal approach, Will.

It may take some control finagling to make sure that the normal fired pool heater is off for a time so you do not double-heat nor over-heat your pool.



In our state, (MA), they require 3 hours between cooling to heating and heating to cooling to avoid the energy waste of pull-down. They want controls to assure that at least 3 hours elapses or the delta-T between fluids is within a narrow band.



So using the pool (or DHW preheat), is a good way to spend the cool-down. Otherwise you could waste it to a dry-cooler but that would be better than spending chiller kW to bring it down.

tim smith

Re: pool as heat exchange method

I did this on a mcmansion here in Seattle. Used the pool as my heat exchanger with watercooled heat pumps. It worked well, cooling is not a major need but rather than have outside noisy condensor fans, Just used the pool. And we did preplan for a sprayer on the pool if customer ever found he needed to cool very often. Usually just leaving the pool cover off was enough here in Seattle. I think your Idea sounds quite cool :0 

Ex Maine Doug

On a smaller scale

I used my pool as the heat source / dump for the house I built in Florida back in early 80's.  High pitched roof with solar panels on the southern side. In the summer when the pool got too warm from the AC, we radiated heat out at night. In the winter the panels collected heat to put back into the pool when the Heatpump was heating the house. 

 In the between seasons the panels added enough heat to keep us swimming. A little 1/2 HP circ moved the pool water out of the pool to the HX and back to the hot tub which overflowed back into the pool. The filter pump had powered valves to use or bypass the solar panels. The HX stayed really really clean.

Big Will

nice

I had hoped this would get some response. It sounds great in my head but I have never seen it done. Its great to bounce this kind thing of you guys. Its like a big water cooler around here. I never thought to use the pool as a evaporative cooler. That would be great on some of these houses with giant pools were they want to hide the condenser..

Roland_18

Heat Sink

Is there an agreed upon water temperature that is considered comfortable? I would think that air temperature and air movement would figure in to it. Just wondering.

Brad White

For pools

it varies in a narrow band. NCAA competitive pools are usually 78 degrees which is cooler than most but then most are burning calories (or hitting on bongs).



For general comfort, 80 to 82 is common, mostly 82F. For elderly folks, 84 is often the case.



The above are for indoor pools where the balance of evaporation and humidity is key and needs mechanical control quite often. (The higher the water temperature, the more evaporation. The cooler the space, the higher the RH. The dryer the space the more the evaporation... it is all a balance.) Also indoor pool air temperature wants to be maintained at least 2 degrees above pool water temperature to reduce chilling when emerging and to keep fogging down.



Outdoor pools? I do not know what limits there may be. My guess is one could tolerate higher temperatures but I have no idea what the comfort limits would be. If I had to guess, as with radiant, 84 would be my peak for any length of time. If anyone knows, I am all ears.

Tim McElwain

The maximum temp

on any pool is 85° F for a number of reasons most of which have to do with certain bacteria which are activated above 95 degrees or typically human body temperature. This is something that has to be monitored in the summer time with heated pools as the sun exposure takes them well over the pool heater set point temperature. It also affects the operation of the pool heaters most of which are copper coil type heating. It is a good idea to have a thermostatic bypass to ensure water goes through the filter and not the heater when temps are above 85 degrees. That along with a number of other issues with chlorine and pool heaters.



Sorry this does not really have much to do with original posting. Many years ago I had the idea of reversing driveway melt systems and using the thermal mass of the summer heated driveway to heat pools. We had a fella on our lines at the gas company that used a separate heat exchanger of a domestic water heater to melt his sidewalk long before anyone was even thinking about such things, he would just let it run by turning on a circulator when it began to snow. Very simple and it worked.

Big Will

so I checked the

temp of the pool today. It is 82 degrees. The weather has been cool in the evenings and around 80 most of the day. every time I am on the roof for more than an hour I notice the pool heater come on so I think letting it absorb some heat would actually let the pool heater relax. My biggest fear is the chemicals in the pool water. I see lots of stainless pool heat exchangers available but I recently had a stainless boiler fail just from taking in evaporated pool water in the combustion air.



I was talking about this idea to one of my guys. He said the belagio hotel In Vegas uses the pond in front with the water jet show as an evaporative condenser. I want to see that mechanical room. I searched on line and could not find anything about it though. sound smart though. Now every time I drive by a building with any kind of pond or pool I think of it.

Brad White

A plate heat exchanger

should probably be used anyway. 316 Ti is recommended. Chlorides are a bear. Ask a local pool chemical company what they use for their pumps and SS parts.



If they use bromine, avoid any aluminum parts. Very aggressive, bromine to aluminum.

tim smith

Re: pool temps etc

I had posted about this job a year + ago. Customer has an outdoor pool uncovered and heats to 92 degrees year around. Her husband has tried to get here to ok a pool cover but she likes the look of the pool too much.  Go figure.

 They were going through pool heaters every 3yrs or so due to the heavy use so finally put a TT 399 and shell and tube heat x w/ cupro nickel tube bundle in, night and day difference.

Mark Eatherton

Interesting Tim...

How much did their fuel use drop?



I'm guessing a minimum of 30%...



ME

Mark Eatherton

Red Cross recommendations...

These standards are from about 20 years ago, but I doubt they've changed much.



If the pool is used for physical exercise, lower operating temperatures.



If it is a leisure pool, 84 degrees F, but in no case, should there ever be more than a 20 degree F differential between the hot tub and the pool.



So Brad, this 3 hour change over. If you get hit in the butt by a fast moving cold front, your clients are basically screwed for 3 hours as it pertains to comfort then eh...



I can see where water to water heat pumps would have a definite advantage over conventional systems. In my minds eye, I see no benefit to delaying switch over so slowly. Regardless of whether you are going from heating to cooling, or vice a versa, energy is energy, and is still in need of transfer in either direction. The only advantage I can see would be in transitioning from heating to cooling and wanting to avoid lifting the heads off the compressors, but that can be handle in system design to limit entering water temperatures using off shelf component/design. As for going the other way, if one uses modcon boilers, they could care less, but if using conventional boiler, the technology (anti condensing 3 ways) is again off shelf to avoid long term condensation production potential.



In reality, this sounds like the perfect application for an intelligent control logic, that would have the ability to anticipate major changes in demand and respond early and accordingly. Something like ENV from Climate Automation Systems.



As for the application of recovering reject heat for swimming pools, excellent idea. The only problem I can see is when you have the most heat to reject, the pool needs it the least. But it would still help during shoulder seasons, and you can control the pool temperature with "water features", i.e. water falls or spray features.



I use to take care of the swimming pool needs for the official Mayors residence here in Denver. It had a water wall / water fall feature, and when that thing turned on, the boilers really struggled to keep up with the load.



Amazing what exposing water to air, and the resultant evaporation effect has on it. Maybe thats why they use cooling towers eh :-)



ME

tim smith

Re: fuel savings

Mark, I don't have any reports yet on this but I should check in with him. I usually check in after a year on most my boiler changes to modcons but this one I have not yet. Mainly I did not expect as much due to just doing pool heat but will be interesting. Stay tuned. Tim