Same results for all pitched roof insulation levels

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My question is why does eQUEST not predict a reduction of energy usage when the EEM is a significant addition of roof insulation for a pitched roof building?

I am a retired environmental engineer and performing an initial assessment of the energy usage at the church which I am a member. I am using eQUEST to make the assessment to present to the finance committee. The church has three buildings which have somewhat different purposes. One building uses an uninsulated unventalated vaulted roof. Two buildings have roof trusses with 8/12 pitch on 24 inch centers.

I got believable results when I added roof insulation to the building with a vaulted roof and no insulation. However, when I got less than 1% reduction in energy usage with the addition of a substantial amount of roof insulation I did not believe that is reasonable.

For the baseline roof, I checked pitch roof and 35?, insulation on the attic floor and R-19 batt insulation. I increased the batt insulation to R-60 for the EEM.? I have selected all of the following roof constructions in eQUEST; 10 wood scissor truss, 24" oc, 2) wood standard frame, and 3) wood advanced frame, 24" oc. I have also selected all the following Ext finishes; 1) Roof, built up Brown, medium; 2) Roofing, shingle Brown, medium; and 3) Felt, bituminous Brown, medium. All produced essentially the same results for both Space Cool Electricity Consumption and Space Heat Gas Consumption. Even when I revised the baseline condition to exclude insulation, the Electricity Consumption and Gas Consumption were all less than 1% different.

Since I got believable results for the first building, I removed the check on the pitch roof and ran the following scenarios with roof constructions of 1) scissor truss, 24: oc; 2) roof deck, 4x beams; 3) wood advanced frame, 24" oc. The results that I obtained were what I considered believable in that there was a 40% reduction in energy usage between no insulation and R-19 and a 20% reduction in energy usage between R-19 and R-60 insulation.

As a result, I believe that either I am entering incorrect information in eQUEST or that eQUEST incorrectly calculates energy usage when the box for pitched roof is selected.

Here are some details on non default information.
Building type: Office Bldg, Two Story
Location: Raleigh, North Carolina
Electric and Gas rates custom: Uniform charges 0.096 $/kWh, 0.77 $/Therm
Shell Area: 15,000 ft2
Bld Orientation: North
Perimeter Zone depth: 20 ft
Aspect Ratio: 3.00
X1: 150 ft,? Y1: 50 ft
Floor Height: Flr-To-Flr 10 ft; Flr-To-Ceil 9 ft
Pitched Roof: checked, 35? w/ 2.0' Overhang, Insulation Location: Attic Floor
Roof Surfaces: See above
Above Grade Walls: Metal Frame, 2x6, 24" oc; Brick, Brown Med, 3/4 fiber bd sheathing; R-19 batt
Ground Floor: Earth Contact; 6" Concrete, no perimeter insul, carpet no pad
Exterior doors:
??? 7x6 glass double doors 4 face N and 1 face E
??? 7x3 glass door 2 face N
??? 7x3 opaque door 1 face S
Exterior windows: Double Clr/Tnt (2006) U=0.55 Alum w/o Brk, Oper
??? 4 x 4; 3% N, 12% S, 16% E, 13% E
Building Operation: Changed Mon to Closed at Noon, Added Sun Noon - 6 pm
Activity Areas: Changed Office (Executive) Percent Area to 20%, Conference Room to 14%. Added Classroom/Lecture with 40%.
Interior Lighting Loads: Office 2.00, Corridor 1.25, Lobby 1.52, Restrooms 0.77, Conference Room 0.92, Mechanical 0.81, Copy Room 1.60, Classroom 1.60.
HVAC System: DX Coils, Furnace. Split System Single Zone DX w. Furn, System,? per Floor
Return Air: Ducted.
Fans: Standard
DHW: Electricity, Storage, 1.5 gal/person/day. Water Temperature, 120? F
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Ron Myers

Ron Myers's picture
Joined: 2018-12-04
Reputation: 0

Check your ceiling construction, do you have insulation on both roof deck and above ceiling?

Check your loads on the output reports, LS-A, B, C, etc? Do you see a difference in the underroof (attic) space?

Wolfe, Josh's picture
Joined: 2018-07-02
Reputation: 0

Is the return air actually ducted? That may be one thing that ?insulates? the heat gain from the airstream.

Also make sure if you have a plenum that you?ve intended there to be a plenum, and if it was intended whether it should be a return air plenum ? these parameters will also affect how much heat gain from the roof makes its way to the space and/or the return air stream.


David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates

David Eldridge's picture
Joined: 2012-05-08
Reputation: 1