[Digestion] Heat input required to maintain optimum digester temp

[Jason Perry]

Greetings all,

I am new to this list and fairly new to biodigesters. I am living in 
Scotland but am originally from northeastern New York. I am working on a 
master's thesis for an MSc program run by the Centre for Alternative 
Technology (CAT) in Wales. The object of my thesis is to determine how 
much of my hometown's energy demand could be met by diverting existing 
biomass waste flows into use as bioenergy feedstocks. This includes 
dairy manure, corn stover, apple orchard prunings, apple waste, etc.

My question for today is this:
How might I estimate the amount of heat input required to maintain the 
optimum temperature in a plug-flow dairy manure digester throughout the 
year in the given climate? I have been playing around with Farmware but 
it is clear that it is only a superficial tool. I realize that this 
figure is going to depend on a huge number of factors, but it would be 
good even if I could establish a range. Perhaps this could be expressed 
as a fraction of the heat value of the theoretical amount of gas produced.

Thanks for any ideas about where I might start.

Jason