Hot Plastic Houses - Understanding Heat Dynamics

From: Dan, Northwest Ohio
Date: 7/1/02
Time: 7:44:25 PM
Remote Name: 63.68.71.247
 

Comments

First and foremost, I am by far not an expert in this area, but have done some recent and quite extensive research on this subject. I have researched and compared 3 types of materials, namely wood, polyvinyl chloride (PVC - a plastic), and aluminum.

First off, BASICALLY there are 2 different factors to consider when we are looking at heat transfer/travel in these various materials. THEY ARE THERMAL CONDUCTIVITY AND RADIANT HEAT TRANSFER.

I will not go into a deep scientific discussion on these but will attempt to shed a little light on the way heat (mainly sunlight) impacts these materials.

Conductive heat is measured by the rate at which heat travels through a material through conduction. The value for conductive heat rates are K and R. We should all be familiar with "R". R is used to rate the performance of the material as it concerns insulation applications. K is the reciprocal (opposite) value of R. K is important as it gives us an idea of HOW QUICKLY OUR MARTIN HOUSING MIGHT HEAT UP OR COOL OFF when heat is introduced into the equation. Both R and K are good indicators as to how various materials respond to to the introduction of radiant heat to their surfaces.

SO... WHAT TO MAKE OF ALL THIS Lower K values for materials indicate slower conductive heating throughout the given thickness of material. This would then go on to say that lower K materials respond less quickly to heat and subsequently take longer to heat up.

Higher R valued materials as most of us know, insulate and retain heat better.

HERE ARE RESEARCH NUMBERS;

Aluminum "K" Value (btu/in/hr/sq. ft./ degree F = 1,643 Wood " " = .333 PVC " " = 2.4

Thus PVC is less likely to heat up as quickly by conductive heat than the other two materials. NOTE!!! Aluminum has a K value that is 1,493 times higher than PVC. IT IS EXCELLENT AT HEATING UP VERY QUICKLY.

On the other hand, materials with high R values loose heat at lower rates.

Aluminum R Value = .00086 Wood = 3.03 PVC = 2.4

Wood retains heat the best, followed closely by PVC.

Color has much to do with the way radiant heat travels through materials. WHITE OR OPAQUE COLORS ARE BEST AT REFLECTING RADIANT HEAT. That is why PMCA recommends painting housing white or having silver roofs.

With this info, you can see that aluminum houses HEAT UP more quickly than PVC (plastic)or wood houses. On the other hand, they cool down more slowly. This is not all bad and I feel there is a place for all three materials. Some are better than others and I have my opinion. ANY HOUSE MUST HAVE COMPONENTS DESIGNED TO ADDRESS HOW THE MATERIAL WILL BEHAVE WITH THE ADDITION OF HEAT. No ventilation IS NOT A GOOD THING. All houses must address ventilation so that the birds remain as comfortable as possible.

With the COLD SNAP OF THIS SPRING, I WONDER HOW MANY MARTINS DIED WHILE IN ALUMINUM HOUSES? It has a very poor R value.

I STRONGLY DOUBT THAT YOU CAN PIN A BLACK RIBBON ON PLASTIC HOUSES. If so, we should have struck ALUMINUM HOUSES FROM THE MARTIN EQUATION LONG, LONG AGO.

Although the material does have some influence on heat up, ALONG SIDE THAT GOES HOW THE HOUSE IS VENTILATED.

Good Luck To ALL, KEEP ON FLEDGING THEM!!!!

Dan