I found this old post where it was explained the vintage construction is a bit worse than ASHRAE to account for thermal bridge.
However, I noticed the vintage construction is actually better than ASHRAE. For example, the wall U-value is 1.6 in the model, while the ASHRAE90.1-2010 indicates U-value 3.293.
Second, I noticed a discrepancy for the HVAC system too. For example, the ASHRAE standard efficiency for condenser water pumps is 301 W/l/s, but the the simulation reports shows the condenser water pump efficiency is 211 W/l/s.
This might have been one of those cases where the constructions taken from OpenStudio-standards were aiming more for realism than the absolute bare minimum acceptable from ASHRAE.
A U-value of 3.293 is pretty close to what you might expect from a single pane of glass. Maybe a single pane of glass would be a little closer to 4 or 5 but, for both single pane glass and a wall with a U-value of 3.293, almost all of the thermal resistance is coming from the air films on either side of the construction rather than the material itself. So, when you have a mass wall made of cinderblocks, you would need an incredibly thin wall to be able to hit an assembly U-value as high as 3.293. Something like a couple of centimeters.
In other words, hitting the maximum U-value acceptable for climate zone 1 in ASHRAE 2010 would probably be more of a challenge than complying with it. Maybe if you made your walls out of a solid steel plate or something. I really don’t know what the ASHRAE 90.1 authors were thinking there other than “there should be no insulation required for mass walls in climate zone 1.”
In any event, I’m sure that the OpenStudio-standards authors probably opted for a construction that realistically embodied the description of “mass wall” rather than some theoretical mass wall that this particular set of ASHRAE criteria is based on.
You may need to cut us a little slack for this one since a lot of the efficiencies of HVAC equipment in ASHRAE 90.1 follow a logic of “if this size of equipment, then this efficiency.” Do you still get this efficiency when you use the HB Sizing Parameter component to set the HVAC eff_standard_ to 2010?
When you do that, the OpenStudio translation first performs a sizing calculation and then sets the efficiencies based on that sizing info before running the simulation. It will increase your overall simulation time substantially but it is intended to help you get closer to the HVAC efficiencies specified in ASHRAE 90.1.
Good to know. I am planning to improve a lot of these methods related to HVAC efficiency at some point soon. Now that they are all written in Python, I’m much better equipped to correct these things. If you find any more efficiencies that you think should be adjusted, let me know and I’ll take them into account when I refactor everything for this.
