I ran this idea past a fridge engineer friend of mine last year, his thoughts where that it would be better to use a fridge rather than a freezer due to freezer compressor operating temps being a lot lower than those on a fridge motor, he reckoned that allthough it would work the motor would be put under more strain due to the gasses involved being outside there design spec.
Your original Post was:
"Would building a container to hold my wine racks insulated with
polystyrene be suitable to maintain wine at a safe temp or not."
Of course it would be "suitable" but building one that actually works is a lot of work compared to finding an upright freezer cabinet.
You made no mention of cooling the wine in the cabinet, just keeping the wine at a "safe temperature" so I suggested an upright (to minimise the footprint) freezer as an alternative to your original plan of building an insulated cabinet.
A freezer has a high level of insulation built in (as opposed to a refrigerator), has airtight seals on the door to minimise the ingress of warm air and will level out the temperatures in your shed.
I pointed out that if the freezer worked it would
be a bonus because the temperature could then be controlled; and freezer compressors
are designed to operate with an inlet temperature from ambient all the way down to about -44 degrees.
Of course, if you do wish to chill the wine, then a large upright refrigerator would be much better and here's one that you might consider ...
http://www.currys.co.uk/gbuk/househ...PLA=1&ef_id=V65ImAAABSgWu53n:20160812220720:s
... at ã179.99 it's an absolute snip, but still much more than I would ever consider paying if I could lay my hands on an old upright freezer cabinet! :thumb:
Depending on where you live in the UK, with a fridge you may need to install a heater for the winter because, with less insulation than a freezer, the wine may freeze.