Hello S_Kirk,
Unfortunately, this could be a daunting task that still might not get you the results you are after.
Ecotect uses a different thermal engine than what PHPP uses, so it could never be similar, unless you were to re-write Ecotect scripts that would exactly utilizes what PHPP uses, in which case you might just as well uses the PHPP spreadsheet and save you the headaches.
There are many thermal simulation engines outthere, and each software will give you various results. I have tested Ecotect against other software before, and did find differences, although not as large as the 6 times energy counsumption you have found.
A lot of the discrepencies can come from the fact that Ecotect does not uses the energy utilized by the HVAC system, only the thermal load that would need to be dealt with by such system. Depending on the HVAC system efficiency, this could vary quite a bit. Additionally, Ecotect does not account for other typical energy losses - or gains - caused by water heaters. Plug loads would have to be modeled individually, which is possible, but quite a bit of a modeling task as it would involve creating either appliance objects and light objects, defining their consumption and giving them a schedule.
I think the biggest difference could also be in the way Ecotect calculates ventilation (infiltration) gains or losses. For starter, the user must enter a ACH for each zone. Note that this is a natural ACH, not your standard ACH at 50 pascal as most softare assume; this natural ACH can be derived from rough formulae - do a google search on that; whereas standard ACH can be tested with blower door tests. Also, if set to "Natural Ventilation", Ecotect will use a formula accounting for the area of glazing in the model, and whether or not there are some potential for cross ventilation (depending on whether or not the glazing are facing each other, 90 degrees from one another, or no cross ventilation at all), then use the wind speed data from the weather file to simulate infiltration losses or gains.
The weather file will also have a great influence on the results. I do not believe PHPP uses the same weather data as Ecotect, which uses the DoE EnergyPlus data (TMY3). For accurate comparisons, you would have to start with exactly the same weather data.
From your results, what is the main discrepancy in the two methods? Where does Ecotect show the most difference with PHPP? Infiltration, conduction? This is easy to analyse using the Passive Gain Breakdown option.
I have not looked into the PHPP spreadsheet in years - it was one of my intention to develop something similar to what you are after, using PHPP formulae to run Ecotect models using scripts, but that would be quite time consuming, and still not very accurate if the weather data is not exactly the same.
From an assembly / conduction point of view, Ecotect is quite accurate as it uses standard formulae. One exceptions is the case of insulated concrete slabs, which are actually hard to model with edge insulation; you would have to first calculate the effective R-value of the edge insulation using standard formulae, then in Ecotect, apply under-slab insulation to match the effective edge insulation that the actual house uses. These are different.
Make sure to set your glazing properties correctly for thermal calculations: set the transmittance to 1.0 and the SHGC to that of the manufacturer, other wise you will be double counting your reduction in incoming solar radiation...
I hope I could clarify things a bit on the various discrepancies.
Let me know if you have more questions on this topic, otherwise please accept as a solution so that others can benefit from this information.
Cheers,
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