Hi All,
I recently did a model where I had the same system in both base and
proposed but I changed the R-Value from 4 (base) to 20 (proposed). I also
changed the window U-value from .80 (base) to .35 (proposed). After I did
the run, I saw only a 5% savings between the heating and cooling use in the
model. When I looked at the loads I saw the base had twice as much cooling
and heating load than the proposed. Does any know why the energy savings
would only be 5% when you have a huge difference between the cooling and
heating loads?
Thanks,
Lee
Is your building in a very mild climate with only a few days per year of
extreme weather?
*Jeremiah D. Crossett*
It is located in Boston, MA.
Are your systems set to auto-size?
Your issue could be part load efficiencies for your HVAC equipment.
*Jeremiah D. Crossett*
Take a look at the energy end-use breakdown between the two runs to see which specific areas resulted in savings. For instance if the building has a lot of lighting and plug loads, the percentage improvement from envelope improvements will be less.
Also the LV report that gives you the design load on the space doesn't include the "system" and ventilation loads, so if your building has a lot of outside air or high minimum airflows that require reheat energy, both of these could make the impact from envelope upgrades become a smaller percentage.
If the form of the building has a lot of interior areas relative to perimeter zones, the percentage reduction from envelope upgrades will be less.
You should also confirm the unmet hours were similar between the two cases.
Last idea - confirm that you modeled the building with perimeter zones and not one-per-floor configuration.
David
David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Other possible reasons:
* Your building is not skin dominated and is internal load dominated - what is the size of your floorplate?
* You are not meeting your loads - check you BEPS or BEPU reports for hours outside throttling range.
Without actually seeing the inp files I'm just guessing.
Vikram Sami, LEED AP BD+C
Hi Guys,
Here all the .inp files. 1.inp is the base and 2.inp is the proposed.
Thank you,
Lee
>From what I see from these input files, the zone AC/Hr went from 0.2 to
0.8. I did not note a change in any R-value from 4 to 20. The increased
ventilation load is the likely culprit.
Could you also share the equest pd2 files so that someone may take a
look at the output?
u-value and air-changes/hr (?). No change on the wall/roof construction.
Also, looks like you are modeling a 3-4 story residential building.
That is correct it is a 4 story residential building. I did a parametric
run were I changed the Air Chang per hour and U-values for the windows and
wall. I only saw a five percent energy savings when I thought with such a
drastic change (Wall R value from 4 to 30), the difference would be much
better. I have attached the file as a rar.
Thanks in advance,
Lee
Lee,
Your outputs show cooling savings around 13% and heating savings 3.5%.
As others have suggested earlier, you need to take a look at every
end-use separately. The heating consumption in this project is driving
your total energy consumption, as heating represents 55% of your total.
I would take a look at measures that might save your heating energy
consumption.
One thing I noticed is that you are assuming almost 90% occupancy 24/7
in this project. This is not typical of a residential building. Most of
your other schedules (for e.g. heating, lighting, plug loads) follow
similar patterns too. I would take a closer look at these, unless of
course these are intentionally set high.
And I did not see any improvements on the walls or roofs. Just on the
glazing.
Best of luck.
I didn't see any changes in the envelope between the 2 inp files you sent me. However the first file (Rindge-1) seemed to have a California weather file while the second one had Boston. When I switched them both to Boston - the numbers were almost identical.
I don't think you have modeled your skin correctly.
Vikram Sami, LEED AP BD+C
Looking at the LS-A and LS-D reports, you seem to have a reasonable change
in envelope loads for the glass changes. That leaves the systems as the
probable culprit. You are using a PMZS for each zone with heat control
constant at 115F and cool control reset from 65 to 56F. With this control,
your envelope loads are only 3% of the total systems loads from SS-D. A
lot of energy is wasted blending the hot deck and cold deck to maintain the
zone temp.
Did you find any differences in cooling and heating capacities (SV-A reports) between the two models?
Kapil Upadhyaya, LEED AP