HVAC, Ice Thermal Storage.

old news.

not revolutionary.

google thermal storage systems.

http://www.encyclopedia.com/doc/1G1-12035633.html

http://energypriorities.com/entries/2007/01/ice_energy_peak_power.php

I visited a shop in texas that uses such a system.

The factor that is needed to make the decision is the delta between peak and off peak rates for electricity, and the cost to operate and install the ice system. BIG enough peak off peak penalty and even an accountant will figure out its a good idea. But THAT IS STRICTLY BECAUSE OF THE ARTIFICAL DISTINCTION OF TIME DEPENDENCY RATES FOR THE SAME KILOWATT.

Its no more"green" than the utility burning the coal.

Its just a technological reaction to cost constraints of peak electricity rate structure. no more dolphins will swim free because they use ice as thermal storage.

Just a a result of peak capacity valuation distortion allowed by the utility regulators. milo

Milo,

GA. I agree.

I do think there may be an indirect 'green' advantage to use of thermal systems. It comes in the form of not needing additional power generation plants to handle peak power demands. If customers were not using thermal storage systems, the power transfer would occur when the demand happens (early to mid mornings in winter possibly). This would increase the peak demand on power plants and possibly require the need to build additional plants requiring resources (material, energy, labor, etc.).

As indicated in earlier posts- most of the time, Ice-based thermal storage is valid only for an economic reason, not as a Green Solution. In fact, because thermal storage shifts power consumption to the evening and away from daytime use, it likely ADDS to the issues of climate change rather that helps make things "better". That is because the shift allows the utility to better use their (likely) coal-fired generators more effectively and eliminates the need for them to fire up natural gas-fired peaking plants during daytime operations. Since the peaking generators are natural gas fired, they create less CO2 than the primary generators.

The reason that ICE is used rather than just chilled water storage is because the ice adds the phase-change latent heat to the storage mix. In addition to a BTU for each degree F temperature differential for each pound of water, ice adds an added 144 BTU per pound for phase change. Of course, since ice is colder, the refrigeration system must make colder fluid so the total refrigeration load is often higher.

Typical Ice building systems use a glycol brine solution cooled to about 22F to make the ice (requiring a 17F refrigerant), compared to a normal chiller making 45F water (with a 40F refrigerant). Based on an 85F condenser water temperature, the DeltaT (and related pressure differential) for making ice is 68F for the ice vs. 45F for the standard chiller. Even allowing for cooler condensing at night (70F) the differential is still 53F vs. the standard 45F. In addition to the added refrigeration loads, the glycol mix has a lower thermal value (requiring more to be circulated) and has a higher viscosity (adding to pumping energy). Net effect- Current ice-storage systems have a 30% higher energy use compared to a standard chiller.

However, it is possible to use Ice-storage in both an economically AND environmentally attractive way. You just have to use the correct systems and operate them in the right way.

My firm has recently developed a totally new style ice-based thermal storage system that solves ALL of the problems that currently plague other systems.

First-

We make 30F sub-cooled water under pressure and release it into an atmospheric pressure tank. The sub-cooled water "flashes" into a slush where the ice float to the top of the tank and the 32F water is returned to the chiller. Making 30F water needs 25F refrigerant, so our DeltaT differential is 45F, the same as the standard chiller, so there is no higher cost to make ice.

Second-

With 32F chilled water, the operating DeltaT of the chilled water system is 29F vs. the "normal" 16F for typical high-efficiency chilled water systems. Normal ice-storage systems make standard 45F chilled water because they have to melt the stored ice and need the DeltaT to accomplish that. Our system uses the return water fed into the top of the slush and the warm water melts the small ice crystals quickly as the water becomes 32F again. That means that the pumps and piping are 45% smaller (saving on installation costs) and the system uses 45% less pump energy (saving CO2 and NOx).

Third-

Because of the 32F chilled water, the air handlers can make 45F supply air vs. normal 55F supply air AND the colder water allows more moisture to be removed so, rather than the normal room conditions of 72F and 50% RH, the room can be held at 78F and 40% RH, which is about the same comfort level but reduces the heat gain from outside for a reduced overall cooling load. The 33F supply air temperature difference will require 52% less air than the normal 17F differential, so the air handlers can be smaller with more installation cost savings in addition to the reduced CO2 and NOx.

Fourth-

Because our system uses a mixture of ice and water, and the ice is less dense than the water, it is possible to measure the weight of the tank and know exactly how much ice (thermal storage) is left at any time during active operation. No other system has this capability.

Fifth-

Because of our ice crystal system, there is no limit to how fast ice can be made or melted so a single storage module can support a large load, compared to other systems that have limitations on how fast ice can be made OR melted and often require more storage units than the required ton-hours of storage would indicate for even higher economic value.

So- you can see now not only how ice-storage is used in an HVAC application but also how it is possible- with the right kind of system- to cut installation costs, operating costs and be Green using ice-storage.

As to what size chiller and storage are required- it is totally dependent on the specific average daily loads, total active operating hours, and how much of the load that is to be covered by the storage system and how much will be covered by active chillers during the peak operating hours. There are several guidelines available to determine those values.

Hope that this helps.