New Construction CalibrationResearch Results and Request for Decision

Regional Technical ForumMarch 18, 2014

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OverviewDecided in February: Supplemental heat in NC homes (Calibration Phase II)

– Use previously approved adjustments (based on RBSA).

Today’s topic: SEEM estimates of total heating energy (Calibration Phase I)

– Is the heat loss effect captured in the previously approved calibration appropriate for NC homes?

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Reminder: Calibration Phase I

Approved (Modified) by RTF on Dec. 17, 2013

Are the captured effects and approved adjustments right for NC homes?

• Compared SEEM (69/64°F) energy estimates to billing estimates.

• Restricted to 429 RBSA homes with well-known characteristics, no non-utility fuels, and clear heating signatures in billing data.

• Regression used to determine adjustment factors that align SEEM (69/64°F) with billing data.

Other RBSA(975)

CalibrationSample

(429)

The Uo Pattern

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y > 0 means SEEM 69/64 > VBDD• SEEM 69/64 < VBDD for

lower-Uo homes

• SEEM increases relative to VBDD as Uo increases

• Average SEEM – VBDD difference roughly constant across high Uo values

Pre-1992 Post-1992 y-axis: percent difference SEEM 69/64 - VBDD

The Uo Pattern

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Examples:• When Uo (Both) = 0.150

SEEM 69/64 averages around 25% over VBDD.

• When Uo (Both) = 0.100, SEEM 69/64 averages about the same as VBDD.

• When Uo (Both) = 0.075, SEEM 69/64 averages around 25% under VBDD.

Pre-1992 Post-1992 What does the pattern mean?

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Adjustments to Account for the Pattern

Calibration adjustments align SEEM 69/64 with billing data.

Primary Heating

EquipmentHeating

ZoneAdjustment

factor at Uo both* = 0.070

Adjustment factor at

Uo both* = 0.075

Elec.Res. Zone 1 1.06 1.04

Elec.Res. Zone 2 0.91 0.90

Elec.Res. Zone 3 0.78 0.77

Gas/HP Zone 1 1.35 1.33

Gas/HP Zone 2 1.17 1.15

Gas/HP Zone 3 1.00 0.98

* Uo both includes heat loss due to infiltration.

The Uo Pattern

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Professional judgment:

• Can’t know for sure since RBSA data doesn’t go that low.

• Would downward trend continue to the left or would it flatten out?

• Right course of action depends on what we think is driving the pattern.

Pre-1992 Post-1992 What happens when Uo (Both) < 0.075?

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The big questions1. What do we think happens for very low U-

values?o Would the downward trend persist, or o Would it flatten out?

2. Should we use different adjustment factors for baseline and efficient cases? o Yes, if trend is caused by Uo (e.g., homes with high heat

loss have lower average temperatures).o No, if trend has some other cause. o Have ruled out several non-Uo culprits (vintage, heating

system type, lack of duct tightness / infiltration tests, …)

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Decision for NC U-value Issue I move that the RTF use RBSA data to calibrate SEEM 94 for single-family new construction, but that the current Phase I model should be modified so that the U variable is constant for Uo (Both) below 0.075. As applicable, different adjustments will be calculated for baseline and efficient cases.

OR

I move something else…

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Additional Slides

Does the calibration sample include Uo values as low as current NC levels? Uo values didn’t change much between 1992 and 2008...

But they seem to have have really decreased after 2008. Graph shows conductive-loss-only Uo.

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20081992

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Does the calibration sample include Uo values as low as current NC levels?

• Lots of post-92 sites (137) but few post-08 sites (9)

• Post-92 sites are fairly well-insulatedo Average post-92 ceiling R-value is 30o About half have ceiling R-value over 38

• But few Uo values as low as we’d likeo NC measures need Uo-conductive around 0.04 to 0.07o RBSA sample’s min is 0.052o Only 6 below 0.055, 16 below 0.060, 44 below 0.065

Additional Slides:How do the adjustments work in measure calculations?

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0.0

0.3

0.5

0.8

1.0

0.00 0.10 0.20 0.30Uo (Both)

SEEM 69/64 Adjustment Factor

Calibration Adjustment Factors

Adjustment factors

• 0.96 for Uo = 0.055

• 0.93 for Uo = 0.065.

• 0.90 for Uo = 0.075.

Graph is for Z2 homes with electric resistance heat.

Adjustments and shell measures

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Example: Shell measure that reduces Uo-both from 0.065 to 0.055 in the prototype house. – This would decrease cold-weather heat loss rate by

0.010/0.065 = 15.4%. – Adjustment factors would reduce savings:

• Efficient case adjustment factor of 0.96;• Inefficient case adjustment factor of 0.93. • This knocks about 3 percentage points off the savings rate.

Additional Slides:What’s causing the pattern?

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Possible Causes

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Assuming the pattern does persist, should savings calculations be based on efficient- and base-case adjustment factors that differ according to Uo?

If pattern is caused by differences in heat loss rates, then a Uo-indexed adjustment factor would be correct.

– Ex. 1: Well-insulated homes have higher average inside temperatures (no cool areas on the periphery).

– Ex. 2: If SEEM inputs are over-stating internal gains, then SEEM must be under-estimating heating energy; such errors would tend to be larger (in percentage terms) for the better-insulated houses.

Possible Causes

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Assuming the pattern does persist, should savings calculations be based on efficient- and base-case adjustment factors that differ according to Uo?

If pattern is due to something else, then a Uo-indexed adjustment factor would be incorrect. (Shouldn’t debit shell measures for things that are accounted for in other measures.)

– Ex 1: Better-insulated homes may tend to have better HVAC CCS than we were able to account for in SEEM runs.

– Ex 2: Very well-insulated homes may tend to have tighter ducts than moderately well-insulated homes.

Someone asked if the low-Uo homes might tend to be large recently-built homes in Zone 3. This doesn’t appear to be the case:

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Uo

Someone asked if the pattern might be due to the fact that a lot of homes didn’t get blower door tests (we imputed infiltration values for these in SEEM input).

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Doesn’t appear to be the case.

If it were, then the pattern should go away for homes that had actual blower door tests.

Someone asked if the pattern might be due to the fact that a lot of homes didn’t get duct tests (we imputed duct leakage values for these in SEEM input).

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Doesn’t appear to be the case.

If it were, then the pattern should go away for homes that had duct blaster tests.

(We already knew about the zonal heat effect)

Is it possible that the apparent Uo effect is partially due to heat source cost-efficiency?

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When cost-efficiency is coarsely coded as “Elec. Res. vs. gas/ HP”, the equipment effect appears to be incremental to the Uo effect.