Hi Barry (gerdes) and Malcolm,
What i know of greenhouses agrees with what Barry has said.
I do want to add that the cooling at night is slowed by the glass covering.
The internal temp stays higher than the external temp. Then is regenerated once the sun hits it.
The same principle applies to solar hot water systems. They work. If your friend is of the opinion that the internal temp can not exceed the ambient then SolarHart and Modern Solar and Edwards and others are in a lot of legal bother.
Again, Is this person worth the effort? I assume it is as you see him every work day.
I know people who believe for some fantastic stroke of logic that recycling water will drain the oceans. Don't Ask. I can not explain that kind of conclusion. That person really believes it. I can say this; he is not capable of dealing with mathematics, subtraction is beyond him. Oh! He does have a current driver's licence.
Cheers