Ice power: Electric Power Research Institute, TVA and Volunteer Energy are conducting a joint test of the 'Ice Bear' in Knoxville, Tennessee. Neyland Stadium can be seen in the background.
Courtesy of Ice Energy
Utilities are installing devices that make ice at night to replace air-conditioning during times of peak power demand.
Over the next few weeks, a consortium of municipal utilities in California will begin retrofitting government offices and commercial properties with systems that use ice made at night to replace air-conditioning during the day. It's part of a pilot program for the devices, which are built by Windsor, CO-based Ice Energy. If widely deployed, they could reduce fuel consumption by utilities by up to 30 percent and put off the need for new power plants.
The first devices will be installed on about two dozen city-owned buildings in Glendale, CA, under the plan being coordinated by the Southern California Public Power Authority. Over the next two years, the 11 participating utilities will install 6,000 of the devices at a total of 1,500 locations, providing 53 megawatts of energy storage to relieve strain on the region's electrical grid. The project is the first large-scale implementation of Ice Energy's technology.
Each Ice Energy device is designed to make ice overnight, when demand for electricity is low, using a high-efficiency compressor to freeze 450 gallons of water. Around midday, the cooling mode kicks in, and the device shuts off the building's regular air conditioner for a six-hour cycle. It pipes a stream of coolant from the slowly melting block of ice to an evaporator coil installed within the building's heating, ventilation, and air-conditioning blower system. Once the ice is melted, the air conditioner returns to normal operation. Brian Parsonnet, Ice Energy's chief technology officer, says the technology can cut a building's power consumption by 95 percent during peak hours on the hottest days.
Cutting demand for electricity during peak hours reduces the need to build new power plants. It also allows utilities to rely on their most efficient power plants, says Ronald Domitrovic, a senior project manager for electric utilization at the Electric Power Research Institute. He says that when utilities fire up their "least efficient, oldest, and least desirable" generating resources to meet peak demand, every increment of increased power on the grid sends costs surging, whether one is talking fuel costs, greenhouse gas emissions, or service reliability. However, at night, utilities draw on their most efficient power plants, which use less fuel than power plants used only during peak hours. The utility also saves energy at other points in the grid--for example, cooler power lines at night transmit electricity more efficiently.
Domitrovic says systems that use ice or cold water on a large scale to provide cooling for campuses and large buildings have "been around for some time." But he says these are usually "expensive one-off units, designed specifically for the building," and that the smaller modular thermal storage systems that Ice Energy provides "can be deployed with relative simplicity" to serve one- or two-story commercial buildings. Ice Energy says that cooling units housed at distributed sites can be networked, presenting utilities with a resource that can be dispatched as needed to help manage demand on the grid.
Parsonnet says the per-unit production cost for the Ice Energy systems has come down from $15,000 for its inaugural model to just $5,000 today. David Walden of SCPPA says that the current models are "cost competitive" with other options for reducing peak power demands, including renewable energy sources such as solar power.
The Ice Energy systems could help integrate more renewable energy into the grid, says Craig Kuennen, marketing manager and project sponsor of Glendale Water and Power, the utility heading up the Glendale portion of the project. He says southern California "has significant wind resources, and those come in at night, when we would be making ice." The Ice Energy systems would provide demand for that wind power, which might otherwise be wasted because of low demand at night.
Evaporative cooling plus drying with desiccants equals cool air for less cost.
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Night time chillers like these have been around for quite a while. When I worked in the Aerospace Industry in SOCal back in the 80's our mainframe was cooled like this. The company took advantage of cheap off-peak energy to chill the cooling pond water, then pipe the water through our mainframe and data centers during the daytime.
Economics of Storing "Coldness"
I am surprised this technology is not much more widespread. It has been used commercially for several years in one form or another and continues to be improved.
I did a couple of projects for Natural Resources Canada a few years back that looked at storing ice/snow from winter for use in summer air conditioning. We started by examining what was being done in terms of much shorter storage times: 24 hours. We talked to dairies that had chilling systems that use nighttime ice builders, and commercial building owners with ice builders incorporated into their building AC systems. The interviewees indicated that their systems provided a reasonable return on investment.
As for long-term storage: Back in Grandpa's time, they actually cut ice blocks from the river and stored them for year-round delivery to peoples' iceboxes. This eventually disappeared, due to the cost of inventorying ice. With today's real estate prices, ice isn't worth storing for any great length of time. That's why modern ice companies buy equipment with enough capacity to meet summer's peak demand, which far exceeds annual demand rate.
For AC/refrigeration systems, 24 hour ice builder systems get around this problem by making "just-in-time" ice, enabling the use of lower priced off-peak electricity AND a smaller cooling system. Cooling systems are sized to meet peak, not average demand. For a given installation, the heat removal needed over a 24 hour period can be provided by a smaller system but it would be inadequate to meet peek cooling demand. The nighttime ice builder system offered by Ice Energy Systems gets around this problem elegantly. The ability to incorporate these systems into a smart grid, as well as other refinements, makes the case for rapid adoption even more compelling.
How many times here in the southwest to you see a chiller or central or window AC unit working it's heart out in the middle of a hot sunny day with the sun beating down on it try to cool its coils. It's just so very stupid to try and cool things during the hottest time of the day. It's like we're too dumb to remember that, without fail, every single day, 10 hours later it will be dark and cool and energy will be far cheaper and many power plants are sitting idle. DUHHHH.
Re: Every AC should be this way
Nope..
here's why
while trying to extract heat from a house in the hottest part of the day and push it outside is certainly not as efficient as it could be, this system has problems:
it is most useful where loads are known ahead, i.e. commercial systems such as power lines that are used regularly.
on some days people may not even turn on their A/C or turn it on only a tiny bit.
This system requires a minimum investment in energy that is spent regardless of the a/c use. this energy is used to chill the water or other thermal mass medium.
And if that thermal mass medium is phase change it can store more energy in a given space but that may not be needed. the huge drawback of phase change is that the phase changes only at a certain temp. this means that using it to modify temp above or below that range doesn't take advantage of the heat storage potential and if the material has been forced to the opposite phase (ice for example) and that cooling is not needed the phase change was a total waste of energy, unless it can be save for subsequent days (with energy loss of storage)
for variable weather, ideally you might need two thermal masses, one for hot, one for cold. of course no system is ideal and is unlikely to be designed like this. they'll just use it for cooling for example.
Guest (aarontco)
is this the most efficient design
I realize that water is a cheap storage medium with a high latent heat. But wouldn't it be better to lower the freezing point using anti-freeze or something similar, so that even more energy could be stored in the same volume of water? It's the same principle as using dry ice, instead of water ice, since water itself can't get as cold. Also, it would seem like good insulation would be key here. A double-walle, vacuum sealed dewar would be ideal, but could be expensive. Cyronics researchers have developed some cheap alternatives that don't require a hard vacuum. I'm just wondering if these kinds of things would improve the system even more, without substantially increasing cost.
Re: is this the most efficient design
The latent heat of fusion of ice, i.e., the energy transferred by the freezing or melting of water equals 334 kJ/kg. By contrast, water releases about 0.6 kJ/kg for each degree C of temperature change. Thus, the property utilized by the technology in the article is primarly based on the ice-water phase change, rather than temperature change or the temperature at which the phase change occurs. I believe the heat of fusion for antifreeze is about 26 kJ/kg, so water is better than pure ethylene glycol. As for water/antifreeze mixtures, I'm pretty sure that pure water has a higher latent heat of fusion. I expect that the water in ice builder systems has some dissolved solids to prevent corrosion, so it would actually freeze somewhat lower than pure water. But the latent heat of fusion would be close to pure water.
Using another substance, such as dry ice, is an interesting idea. Dry ice (solid CO2) goes from a solid to a gas at atmospheric pressure with a heat of sublimation of 645 kJ/kg or 93% more energy per kg than water. Great, except that making dry ice from CO2 gas requires more expensive equipment than making ice from water.
Re: is this the most efficient design
In my post shown above, I made two errors concerning thermal properties, Here are the corrections:
1. It takes 4.18 kJ/kg (not 0.6 deg) to raise water one deg. C
2. The heat of fusion for ethylene glycol is 181 kJ/kg (not 26 kJ/kg).
Sorry about that folks. Nevertheless, These corrections don't influence my conclusion, supporting the practicality of using the ice/water transition to store energy.
Guest (DockScience)
Re: is this the most efficient design
There is an additional penalty for getting too cold, humidity. You really don't want sub-freezing temperatures for use in a air cooling system.
If the liquid/air heat exchanger gets really cold, the heat exchanger has the both the risk of freezing up as well as the issue of lowering the humidity too much and making a dry uncomfortable indoor environment.
Re: is this the most efficient design
This is not a concern. Water to air heat exchangers (commonly referred to as coils) can be selected on the basis of leaving air temperature. Furthermore, the system designer may temper the chilled water by using a 'mixing valve'.
If the 1,500 units cost $5K (without installation) each to save 53MW, thats 7.5M/53M or $0.15/W. That's way less than the gas fired peaker plants it replaces, and less than the ~$4.00/W-installed solar.
Wouldn't the same principle be usable in a refrigerator, so it could avoid peak daytime rates?
The original version of this story incorrectly stated that the project will involve 1,500 of the $5,000 devices. Actually, there will be 1,500 sites, with a total of 6,000 devices.
1) Allow people to work in shorts, and raise the office temperature accordingly.
2) Have some gov't sites open only from 0500 to 1300 during the summer.
As a roofing contractor and material supplier for 31 years I could not but notice the inefficient roof around the test unit. I have been using non petroleum based roof coatings made in the US since 1980. The roof pictured goes to 140 degrees F on a day with clear sky's and an ambient temperature of 85 degreed F. Our coatings never exceed 92 degrees F. We have taken up to 40% off air conditioning bills by changing the roof color. The technology for the copying machine dates from the 19th century. We can not wait decades before implementation of available solutions. These guys need to get with the program.
I couldn't agree more. Flying into most cities in the southwest US and you see roof after roof with every color but white. In the 70's scientists and policy makers found the most cost effective means of saving energy was through conservation.
Turning roof colors white and installing materials with a better insulating and reflection characteristics would go a long way!
I also believe that the off peak ice generation and storage idea has just scratched the surface.
This sector could also generate a lot of good jobs!
Chilled Water Ice Storage Systems are affordable
The Statement from EPRI representative Domitrovic "says systems that use ice or cold water on a large scale to provide cooling for campuses and large buildings have "been around for some time" is true. Products have improved as well as applications and operational best practices. He goes on to say, "these are usually expensive one-off units, designed specifically for the building.'
That last statement is not true. Today's chilled water ice storage systems are modular and can be easily and affordabley adapted to most buildings. The 2008 ASHRAE First Place Institutional Design Award Project went to Fossil Ridge High School in Fort Collins, CO. The cost to build that school with partial ice storage was comparative to a sister school constructed without storage.
To say ice storage systems for chilled water cooling designs are one-of units is not the case. I would ask EPRI to take a look at the great work and decisions engineers are making in their energy storage hybrid cooling designs with chilled water. The designers are finding synergies with pumping both fluids and air further improving efficiency.
The manufacturers make modular tanks with cataloged performance. With todays better design tools and best practices affordability, performance and reliability is not a leap of faith, it is reality.
Thermal Storage Systems may be news to the writer, but this technology is old hat to the HVAC world. Take a look at Calmac ice storage tanks.
Typically, the implementation of these systems does not depend upon the suggestion and guidance of engineers, but upon the wisdom of the financial geniuses who define energy policy.
In this case what matters is 'off peak' electrical rates (many pages) and subsidies.
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1 Comment
existing system for heating
We have in our house a similar system for heat. At night, the system heats up a large suitcase sized box of bricks when the electricity costs are reduced. During the day, fans pull heat from the box. We heated our house in Michigan for about $100 dollars a month over a very cold winter. Nice to see a summer version for cooling.
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