If an automotive radiator was being considered - and the money was present in the budget, of course - shopping around for the cheapest of the cheap
new one would be better. At least in the Untied States, the percentage of vehicles which go through their entire lives with the same coolant that was put in at the factory (with only "top-ups" when absolutely necessary) is staggering. I noticed the same with people's automatic transmission fluid and filter. ("There's a
filter in there?! Wait, you mean it's not
supposed to smell like that?")
I know you are talking about a relatively small amount of heat, but might as well make sure that whatever heat-exchanger you end up going with is an efficient one. New products will also minimize the contaminates in your system.
They're not hugely popular, and never really were, but some people still use Fresca Sol brand products to set up water-cooled HID lights, and they might be producing more heat. Doing a search to find out how they cool things might give you some additional ideas (but you may already have a better one in mind, who is to say?). I've read of people using a large reservoir in an unheated space such as a basement and perhaps skipping any other means to cool their heat-transfer fluid other than allowing the reservoir to cool naturally during the "night" period. I suppose that would depend on the amount of heat the person is dumping into it and how much of that heat the fluid is able to lose during the lights-out time; if such a setup is not able to keep up with the heat being produced and/or if each new "day" begins with the coolant still holding some of the heat that was produced from the day before, then a more active solution would be required.
I have read of the above kind of thing being done with a swimming pool or even small pond as the reservoir. Probably not an option if the gardener lives in an apartment, though
.
I once spent some time wondering about the feasibility of setting up some kind of "holding tank" that went between the cold-water line and the person's residential water heater. Any heat that was added to its water would merely cause the water heater to have less work to do, lol, and some of the holding tank's contents would be removed - and replaced with cold water from the main or the person's well - here and there throughout the day. But I was using air-cooled reflectors at the time and the concept seemed a little...
involved when I didn't need anything other than what I already had. And it (depending on the size of the holding tank, I suppose) would depend on the level of hot water use; if that amount was minimal then it would basically be back to the "just a large reservoir" thing.
Rambleramble...
I like it ^^ But the problem is, when u are just in an apartment it would be hard to do something like that, but if u have a house it would really be an option!