From: black.hole.4.spam{at}gmail.com (Don Hills)

Some more data:

From several sources, the general wisdom is that insulation is cheap at the
build stage but expensive to retrofit. Even older frozen food stores appear
to be well insulated, and adding significant extra insulation would not
greatly increase the efficiency. Refrigeration plants are more efficient
than they used to be so there's always been an incentive to minimise the
plant cost by maximising the insulation. There are bigger savings to be
made in other areas.

I found a couple of papers which go into this in considerable detail.

This one discusses the same energy storage / usage shifting technique that
started his thread, using a US based example:

 http://www.irc.wisc.edu/file.php?id=53>

This one generally discusses ways in which energy may be saved:

 http://www.baseco.com/Publications/ACEEE%202005%20-%20Energy%20Efficiency%20i
n%20Fresh%20Fruit%20and%20Vegetable%20Processing.pdf>

I also found some discussions on frozen fish storage, which is an extreme
case as it is typically stored at -30C or below instead of the -20C to -24C
for frozen vegetables. In summary, it typically takes as much energy to
freeze it in the first place as it does to store it in a large cold store
for 4 to 6 months at -30C.

So in summary:

IF there is a significant difference in cost between peak and off-peak energy,

AND IF the refrigeration plant has sufficient capacity (or can be
economically upgraded) to handle a partial or complete load shift,

AND IF energy consumption by cold stores is a significant part of the total
grid load,

THEN energy storage in cold stores can provide effective load shifting.

Personally, I think they're a much smaller part of the grid load than the
processing and freezing stages which are less tractable in terms of load
shifting. The figures in my earlier post and the frozen fish figures both
tend to bear this out. Goods don't often spend much time in a store unless
they're seasonal supply items such as fruit, further biasing the energy
usage towards the freezing stage and away from the storage stage. So while
it may make sense to energy store / load shift from the owner's point of
view (reducing running costs), it may not be a big enough overall saving of
peak load on a grid-wide basis to be useful in postponing the requirement
to build more generating capacity.

What we need now to complete the analysis is some figures on how much
energy is used to run cool stores compared with overall consumption.

--
Don Hills    (dmhills at attglobaldotnet)     Wellington, New Zealand
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