A box of heat

Our energy outlook continues to evolve with the rapidly changing times. With the talk of electrification, fuel shortages, and changes to rate structures, there is a lot that is currently up in the air. Since the beginning of time, people have looked for ways to create and store heat energy. The focus on energy storage seems to come and go. It may be driven by economic changes, incentive plans and/or consumer desire to be more energy independent.

One technology that relies heavily on thermal storage is solar thermal, used for heating applications. You have a solar window available every day the sun shines to grab that solar radiation. The motto in solar thermal has always been: use it or lose it. We have been chasing ways to harvest and hold this energy since caveman days.

I have been through three solar renaissance periods now. There tends to be a cycle of years around oil embargos, shortages, and global unrest. These energy scares drive consumers to look for options with solar thermal and thermal storage.

Luckily for those in the HVAC, plumbing and hydronic trades this presents some great opportunities. We know how to wrangle fluids such as water and refrigerants. In the hydronic discipline we use water or water mixtures to move and store energy. Water works nicely as a medium. It is affordable, readily available, safe and understood.

Once we combust a fossil fuel to change the state to hot water for example, we start losing a percentage of that energy. So, we would like to get as much of the energy, now contained in water, into a well-insulated container, to bottle the genie. Insulated tanks store heated water nicely. An almost unlimited selection of tank types, sizes, piping connections, insulation options are available. Custom tanks can be built for applications from many metals and composites. Collapsible non-pressurized tanks are also used for limited access applications.

By Bob “Hot Rod” Rohr

Sizing a storage tank

The math involved in sizing a storage tank is fairly straight forward. Knowing the capacity of the tank, type of fluid and temperature delta, we can come up with a thermal storage plan and sizing information.

How much energy (h) could we store in a 100-gallon tank, heated from 70°F to 180°F?

Formula 1 h= 8.33v (∆T)° h= 8.33 (100) (180-70) h= 91,630 BTUs

Where: h is energy v is volume