BEopt to HERS comparison.

 

After evaluating BEopt 2.2 for the first time recently it accrued to me that the output source energy results should be able to give an equivalent HERS rating. The HERS index is being promoted as a home quality indicator by a number of industry proponents and realtors.  Has NREL considered this? 

 

The HERS index is based on the difference between a reference home and the designed homes energy use called either source energy (NREL) or consumption energy (Rem/rate).  If all things are equal these energy levels should be the same. Am I correct in assuming that you are using the equations in the 2006 Mortgage Industry National Energy Rating Systems Standard?

 

The first issue would be the reference configuration.  The HERS reference home is based on the IECC 2006 configuration, which represents 100 on the HERS scale.  The IECC 2009 configuration is 15% below that shown for 2006 and represents 85 on the HERS scale.  BEopt 2.2 states that its U10 benchmark reference home is based on IECC 2009 but it appears to align with the 100 scale of 2006. Could you please clarify?

 

I based my analysis on my 2012 LEED gold home as the design had a RESNET HERS rating using REM/Rate Software.  I downloaded the newer 14.4 version of REM/Rate software and re-inputted the original specifications and verified that the HERS rating was the same.  It was.

 

The rem/rate program resulted in a HERS rating of 46; however, I was using a dual fuel HVAC system that BEopt does not support, so I converted both applications to use a conventional air based heat pump system.  The rem/rate HERS rating increased to 52. 

 

I then drew the design in BEopt and as close as possible inputted the rem/rate data.  The conditioned space came out within 140sq ft (4200 rem/rate, 4340 BEopt).  My design had curved bay window walls that I had to equalize in BEopt using rectangles using the same area.

 

Rem/Rate expects you to add the mechanical equipment from a manual J and D calculation, or roundup from the design loads in KBtu/hr.  They also show the annual loads in MMBtu/yr and consumption in MMBtu/yr. Rem/rate does not show reference values although one can establish total use via the HERS index.

 

The following table shows the correlation results:

 

 

Rem/rate

Rem/rate

BEopt2.2

BEopt2.2

Design Loads

KBtu/Hr

Output round up KBtu/Hr

Output KBtu/Hr

Adjusted to match Rem/rate

Heat

31.3

36

29.34

 

Cool

22.3

36 (3 ton)

2.91ton (35KBtu)

 

 

 

 

 

 

Annual Consumption/Source

MMBtu/Yr

 

MMBtu/Yr

 

Heat

20.8

 

22.4

24.5

Cool

5.8

 

5.8

3.8

Water

18.6

 

19.4

18.6

Lights & Appliance

33.8

 

23.2+25

17.4+18.2

Vent Fan + pump

(VF 2.98)

 

4.1+7.7

4.8+7.5

Misc

 

 

46.5

Removed

Total

78.9

 

154.1

94.8

 

 

 

 

 

HERS Ref 100

152

BEopt Ref

226

179.5

HERS Index

52

HERS Equivalent

68

52.8

Efficiency Improvement

48%

 

32%

47.2%

 

 

 

 

 

 Heat and cool only

26.6

Design

28.3

 

 

 

BEopt Ref

81.1

 

 

 

HERS Equivalent

35

 

 

BEopt has a number of categories that Rem/rate does not; the most glaring is the miscellaneous group. The Misc category is the same for both reference and design and therefore distorts the efficiency ratio.  If removed on both sides the ratio moves close to that of HERS (column 5).  By adjustment and comparison between the two input files the correlation improved (see adjusted to match rem/rate column).  Further adjustments reduced the design down to 94.8 and HERS ratio of 53, so I believe it is possible to provide a HERS type comparison.

 

I believe there should be a subset of requirements for residential home quality; the first being the energy efficiency or quality of just the building (see heat and cool only section in table).  This addresses builder quality of the envelope construction alone.  Rem/Rate has added HERS before PV and after PV as PV distorts the rating by compensating for poor construction and poor energy efficiency.

 

I hope the above makes sense, and I am very interested in understanding NRELs position on BEopt providing a HERS equivalent rating.  If this is possible it would make a big difference to BEopt acceptance.  The RESNET Rem/rate solution is a provider and software environment that has a locked-in system of expensive software licenses and multiple provider fees.  All these costs have made it almost impossible for energy raters to make a living, and many have had to either work for contractors or find another career.  This means they cannot act independently and in the best interest of their customers; it also makes it expensive for homeowners to have comprehensive audits, so they resort to the strip-down $99.00 offerings from utility companies that are also supported by local contractors on the premise they can get additional work from the audit to make it pay; hardly independent and in the best interest of the homeowner.

 

On the other hand as BEopt is a no cost product and if it provides a HERS equivalent rating the game changes and in favor of the raters and their customers.

 

Looking forward to a response

 

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