Storing the winter's "cold"

A place for topics that don't easily fit other categories.
thenickjones
Posts: 2
Joined: Sat Jun 07, 2008 11:49 pm

Storing the winter's "cold"

Postby thenickjones » Sun Jun 08, 2008 12:18 am

I have been interested in the idea of storing the winter's "cold" as well as the summer's heat for a while now, and I had a specific question about the freezer mentioned on this website. While it may not be practical to reach sub-freezing temperatures with ice stored from the winter, have you ever considered a similar system to your freezer based on storing "cold" in ice? It seems to me that the heat absorbed by the ice's shifting from solid to liquid would greatly outweigh heat absorption of sub-freezing brine, but I don't really know how I would go about calculating the difference. I doubt that sub-freezing temperatures could be reached, but if one were only interested in refrigeration and air conditioning, I wonder if storing up large amounts of ice in the winter could prove economical on a residential or even commercial scale? I would be very interested to hear any thoughts or experience that you may have on this subject.

Nick

User avatar
Bob
Posts: 631
Joined: Tue Jul 03, 2001 11:01 pm
Location: Willow, Alaska USA
Contact:

Re: Storing the winter's "cold"

Postby Bob » Fri Jun 13, 2008 1:51 pm

Hi Nick,

I don't have time for more than a quick "drive-by" response right now, but wanted to respond with something...

...if one were only interested in refrigeration and air conditioning, I wonder if storing up large amounts of ice in the winter could prove economical on a residential or even commercial scale?

Yes, that's an interesting idea. There are larger scale systems in current use that do something similar, but they are mostly aimed at more efficient use of off-peak power. Use electricity to make ice at off-peak rates when it is cheaper, then melt the ice during the heat of the day -- a phase-change heat sink. (Try googling "Thermal Energy Storage" and off-peak, for examples.)

As far as calculating the economics of seasonal storage, I don't know. It might start to get more interesting as the cost of electricity continues to rise. See also the Price Residence on my representative projects page. It describes one way to get a lot of capacity without breaking the bank, but doesn't take advantage of phase-change.

As I see it, the issues probably come down to the first cost of the storage capacity (e.g. water tanks?) required to store that much "coolth", and the amount of surface area required to make enough ice required to see one through a cooling season. (e.g. note that even in Minnesota, lakes don't freeze all the way to the bottom.) To get enough surface area exposed to the winter coolth, you'd need many smaller water tanks, rather than one big one. Or lots of coils of piping in a large tank, etc. -- all of which adds cost & complexity. Tradeoffs between surface area and volume become a problem.

It seems to me that the heat absorbed by the ice's shifting from solid to liquid would greatly outweigh heat absorption of sub-freezing brine

Actually, that is the principle used in the freezer as well. All the brine does is lower the freezing point. It stores & releases the same Btus/lb as water.

thenickjones
Posts: 2
Joined: Sat Jun 07, 2008 11:49 pm

Re: Storing the winter's "cold"

Postby thenickjones » Sun Jul 20, 2008 11:49 am

Bob,

Thanks for the reply. I've heard of the ice systems used on a commercial scale in order to harness the use of off-peak power. Though they address the bottom line of a commercial enterprise, they don't interest me as much as using a more natural source of ice.

I still haven't sat down and calculated the BTUs stored per module of ice for a cost-benefit analysis, since I will most likely have to create some pilot systems in order to determine the BTUs lost to ambient temperature differentials, so I would be very interested in hearing some more details of your brine freezer design.

I have been envisioning a modular system, where one insulated module of ice is stacked vertically on top of others as they freeze all winter. During the summer, the system will be automated to melt the top module of ice first, and the melt water from this module will drip down onto the porous outer skins of the lower modules, cooling them directly and with another phase change as the melt water evaporates. The idea is to minimize unnecessary melting and stretch the ice supply as far as possible.

When you have the time, I would be very interested in hearing more about what you have learned from the design and implementation of your ice system.

Nick

User avatar
Bob
Posts: 631
Joined: Tue Jul 03, 2001 11:01 pm
Location: Willow, Alaska USA
Contact:

Re: Storing the winter's "cold"

Postby Bob » Mon Jul 21, 2008 2:09 pm

I still haven't sat down and calculated the BTUs stored per module of ice for a cost-benefit analysis, since I will most likely have to create some pilot systems in order to determine the BTUs lost to ambient temperature differentials

That is something that can be designed / engineered before actually building (or spending the money to build) anything. You need to start with the design cooling load for the space you want to condition. Then you'll need to know (or decide) things like the weight, size and shape of each container, climate data for your site, amount of insulation, etc. The problem with a pilot-scale system is that system performance depends on things like volume and surface area, which will be different, depending on scale.

The idea is to minimize unnecessary melting and stretch the ice supply as far as possible.

The desired rate of melting will be depend on calculated cooling load. I.e. the rate of heat gain for the space you want to cool, that you need to offset.

These are the kinds of calculations and designs that mechanical (HVAC) engineers commonly deal with.


Return to “General Catchall”

Who is online

Users browsing this forum: No registered users and 1 guest