Automotive radiator for use as a solar collector?

[dave123]

I was at the home improvement store the other day, checking out copper tubing and such for a future experiment in a solar hot water heater, when I thought about just simply using a car or truck radiator mounted in an insulated box with a glass top.  I wasn't planning on running potable water directly through the collector anyhow, as my plan is to use a water to water heat exchanger and using propylene glycol for the heat transfer medium.  This will be for an occasional use system, and so I don't want to have to worry about draining/refilling the heat transfer fluid to prevent freezing.

Any comments on using a radiator?  It is already of decent flow, with good mass for heat absorption, and even painted black!  I don't have any old ones laying around to date, but have taken others in for minimal scrap money in the past.  

[commanda]

Automotive radiators rely on airflow through it to transfer heat. It won't work very effectively the way you plan on using it.

Amanda

[Tyler883]

A radiator works well to cool a fluid because it provides a large surface area for cooler air(w.r.t. the fluid) to flow past.

As a heater, it would work well if you could pass warmer air( w.r.t. the fluid).

However, collecting heat from the sun might not be any more efficient than the rad pipes in a box with a thermal heat mass next to them.

[hvirtane]

I've not used them myself,

but have seen others using them.

They are not the best, but they do work.

If the radiators are free, why not

using them.

- Hannu

[zmoz]

A much better investment is 3/4" black plastic tubing. It's dirt cheap - about $18 for a 100 foot roll. I have made a pool heater using this - 200' of tubing coiled up, the water coming in is around 70 degrees, the water going out is around 82 degrees. It would heat a 5 gallon bucket of water to over 100 degrees in less than 15 minutes.

[Roamer195]

If you're building a 1X solar box, the radiators are worthless.

On the other hand, if you're building a reflective concentrator, the radiator is a cheap and superior collection point because it allows the heat to pass very quickly into the liquid (small parallel passages). Just make sure you don't let the fluid-flow come to a stop or things will be glowing in pretty short order.

Also, if you have it mounted in an insulated metal box with only the "hot" face side open to the air, you'll retain most of the heat you collect without it radiating away.

Old ovens have plenty of scavengable high-temp insulation. If you find a small enough radiator you could probably just take off the oven door and put the radiator inside.