Cooling with Hot Water Heaters

Solar hot water heaters are considered one of the most cost effective ways to add a renewable energy source to a home or business. Another way to decrease your energy bill is to take advantage of technologies that consider the cost of energy as a factor of the time of day, one approach that does this very effectively is the production of ice at night to aid in cooling during the day.   (wow this is feeling like I'm writing a report for 9th grade science, but darn it I have no better intro coming to mind)  Several months ago I asked myself if it might be possible to find some kind of synergy between these two technologies.  

For engineers and people who understand my ADD I will provide the quick and dirty thusly immediately below.  As I have time I will add explanations at the bottom, or as requests for clarification come in.

Figure 1

The concept I am presenting here is based on the fact that optimal cooling systems are as close to black body ideal bodies as possible.  The collectors in a solar hot water heater have a relatively large surface area and are painted to behave as a black body.  Traditionally this trait goes unused for half of the day, what I am curious to see, is would it be possible to utilize the black body characteristics for night time cooling, most critically would it be cost effective to utilize the configuration I propose or something similar to it?
To minimize cost, the design shown Figure 1 utilizes a single hydraulic pump and a flow switch that alternates between the two heat exchangers.

Figure 2

  As day turns the night the characteristics of the system will change in a few critical ways.  First and most obviously the flow switch will alternate from having the working fluid move past the Water Heater to the Refrigeration Radiator Augment (yeah I know the name isn't sexy, I'm an engineering geek not a marketing guru, whaddya want from me?) The altered configuration is shown in Figure 2.  For the system to be used as an effective additional convection and black body radiation cooling surface, to augment the standard radiator found on refrigeration systems, the body design will need to under a range of potential configuration changes.  With respect to radiative cooling, the insulation layer that is so critical for day time operation must have the ability to either dynamically alter its thermal resistivity or physically rearrange itself to allow for maximum exposed surface area to the ambient environment.  To increase the overall efficiency of the system convective cooling should also be considered and a design that promotes both active and passive air flow, at night, could drastically alter thermal performance.  One potential approach is roughly shown in Figure 3

Figure 3

 What Figure 3 attempts to convey is that, warm working fluid is piped up through the base of the cooling system, which has expanded itself to aid in nighttime reverse energy transfer.  The glass covers which kept heat in during the day are now open to the night and letting infrared radiation and warm air escape into the night, additionally fan(s) might possibly be used to promote forced convection to aid in the cooling process.  One way to power the fan system might be to utilize some kind of thermal electric generator to minimize the system's energy demands.

Overall I am really curious to see whether or not a design like this would actually be more energy efficient than using the two technologies separately.  The solar hot water characteristics are rather known and the financial models for the technology are readily available and the cost analysis of implementing an HVAC system that utilizes night time cooling can be done by any number of contracting agencies.
       
               The real questions for the system's theoretical synergy stems from the fact that heat syncs experience diminishing returns on their ability to transfer thermal energy. Would this system only be considered beneficial if it was manufactured as a single platform, reducing the amount of radiator surface area built into the actual AC unit?  Could it be utilized as a way to augment existing systems as a way to lower energy costs?  While I can put together the basic equations I unfortunately don't have the resources to do an in-depth analysis on the potential ROI if there is any.  Realistically I  have my own doubts about this concept, no matter how cool I think it is, simply put there are too many moving parts that need to be factored in to the system's design and sadly moving parts/having more parts generally = greater overall cost.  Anyways I hope this at least gave you something to think about, please feel free to provide your own input.

The basic concept of a solar hot water heater is relatively straight forward, a number of pipes are coated in as dark a material as possible, the closer to true black the better.  As sunlight is absorbed by the pipes the energy of the light is converted into heat energy.  This heat energy is transferred to some kind of carrier liquid, with respect to what I will be describing this liquid will be any material that will not freeze or boil within the temperatures normally seen on the Earth's surface (-70 F-250 F).  The carrier liquid will move from the heating pipes through a pump until it reaches the heat exchanger, at the heat exchanger the warmth from the carrier liquid will be used to pre-heat a water source, before that water goes into a hot water heater.  After the heat exchanger the carrier liquid is cool enough to be cycled back towards the hot water heater.