cargo compartment questions

[cattlerepairman]

With respect to commonly used medium and long-haul passenger aircraft (any type you are comfortable talking about):

Can someone outline how heating and cooling of lower deck cargo compartments is accomplished? Is there a direct air exchange (air vents removing air from and/or supplying air to the compartment) or is heated/cooled cabin air just passed along the outside of the cargo compartment walls to facilitate a temperature change?

How do cargo compartment temperatures compare to cabin temperatures?

Is there a technical difference with regards to heating/cooling between class C and class D compartments?

How does one verify by looking into a cargo compartment whether this is a class C or a class D compartment?

I hate double-posting, but I had no luck in the engineers' forum with those questions.

[HZ123]

747/777/A340 and many others have 2 Holds sub divided into 5 Compartments. Forward holds have no heating so minus temperatures in flight. Compartments 3, 4 and 5 comprise of Hold 2 and adjoin. However, compartment 5 is heated for the transport of pets and livestock. Usually this is the tapered area at the a/c rear. The bins / containers will normally form a barrier to retain heat within that compartment. On opening the rear hold doors the area is often comfortably warm long after the cargo has gone.

I have no doubt our engineering contributers can furnish tech info and prescise temps.