Thank you all.

The advice above is great and I will follow up on it. Is RP-1404 available
from the ashrae shop?

I actually did a crude implementation with excel goal seek. I used weather
data an the event fixture diary for input variables and bulk parameters
representing heat loss, parasitic and hot water. This was sanity checked
against plant capacities. This approach probably wouldn't be adequate for
ipmvp but will hopefully prove sufficient for our current purposes.

I'm pretty awful at statistics. I know there's no excuse for this
considering it's prevalence in what we do so working through a Udacity
course.

Mnay thanks

Chris