Hello...
I have been working out the heat loss for rooms in a new build (140mm timber frame with 140mm insulation, cavity, 100mm block and render) in order to specify correctly sized radiators but I am getting very different results depending on the method that I use.
Method 1 is where I calculate the heat loss for all surfaces based on the U-Values for the surfaces in question.
Method 2 is where I simply calculate the volume of the room, and make some basic corrections (e.g. north facing, french doors, number of external walls, etc).
The problem is, if I take Bedroom 1 (which is 3.8m x 4.8m with a ceiling height of 2.7m, 2 external walls, and set of french doors) and apply Method 1 I arrive at a BTU requirement of 2700 BTU's (791 Watts), and if I use Method 2 I arrive at 6405 BTU's. The results differ by a factor of over 2!
Given that Method 1 involves explicitly calculating heat loss of all surfaces and temperature differences between the inside and outside of these surfaces I would think method 1 is the most accurate method and Method 2 is just a crude estimate, but the difference seems substantial. But maybe my thinking is incorrect or I am missing something!
Any thoughts?
P.s. I have posted a spreadsheet online at the following url (just click at the top of the page to move between the two methods(sheets):
http://spreadsheets.google.com/pub?key=pmaiDN932ryiMM3UyaJfKVg
P.p.s....
www.trademate.co.uk heat loss calculator arrives at 3275 BTU's
www.plembcentre.co.uk heat loss calculator arrives at 1356.8 BTU's
I have been working out the heat loss for rooms in a new build (140mm timber frame with 140mm insulation, cavity, 100mm block and render) in order to specify correctly sized radiators but I am getting very different results depending on the method that I use.
Method 1 is where I calculate the heat loss for all surfaces based on the U-Values for the surfaces in question.
Method 2 is where I simply calculate the volume of the room, and make some basic corrections (e.g. north facing, french doors, number of external walls, etc).
The problem is, if I take Bedroom 1 (which is 3.8m x 4.8m with a ceiling height of 2.7m, 2 external walls, and set of french doors) and apply Method 1 I arrive at a BTU requirement of 2700 BTU's (791 Watts), and if I use Method 2 I arrive at 6405 BTU's. The results differ by a factor of over 2!
Given that Method 1 involves explicitly calculating heat loss of all surfaces and temperature differences between the inside and outside of these surfaces I would think method 1 is the most accurate method and Method 2 is just a crude estimate, but the difference seems substantial. But maybe my thinking is incorrect or I am missing something!
Any thoughts?
P.s. I have posted a spreadsheet online at the following url (just click at the top of the page to move between the two methods(sheets):
http://spreadsheets.google.com/pub?key=pmaiDN932ryiMM3UyaJfKVg
P.p.s....
www.trademate.co.uk heat loss calculator arrives at 3275 BTU's
www.plembcentre.co.uk heat loss calculator arrives at 1356.8 BTU's