A Google search of "In ground radiant heat for greenhouses" brings up a variety of places to look. A magazine like Greenhouse Grower or some related publications might have articles that could be found with a search on their website. If you have a good Co-operative Extension office in your county they might be of help in researching the topic also.

I have only ever used it in concrete as that is what fit our needs, Once you experience it you will be amazed at what benefits it can have.

Sand. if you're interested, look up this topic in the farm show.