# Presentation: 496664

## Performance Codes are Actually Easier:  A Different Paradigm

- 2000 National Workshop on
- State Building Energy Codes
- New Orleans, LA
- July 12, 2000
- Philip Fairey

## A Simple Rule of Thumb

-    **“****Building science is just like space science, only more complex.”**

*Terry Brennen*
-    Physicist & Building
-    Forensics Expert

## Compliance Methods

- _Prescriptive_ - disallows compliance if any single component fails to meet its prescribed  minimum requirements.
- _Performance_ - compliance based on achieving equal or lower estimated overall energy use than a “twin” (reference) building.

**Most Codes allow two pathways**

## One Versus the Other

_**Prescriptive**_
**Pro:**  simple and easy to use and enforce.
**Con:**  flexibility is severely limited to a small group of  options.

_**Performance**_
**Pro:**  virtually no limit on available options.
**Con:**  requires detailed estimates of energy use in buildings.

**The pros and cons of methods**

## “Trade-off” Methods

- Allows user to “trade” a ‘less than required’ performance in one component for an equally ‘better than required’ performance in another (e.g. trading poor envelope insulation for better equipment).
- Most often characterized by complex, difficult to follow tables, nomagraphs, equation, charts, etc.

**“****Quasi” Performance Methods**

## “Measuring” Performance

- All performance-based energy codes are based on “energy budgets.”
- The energy budget for a building is determined from its reference “twin.”
- Different systems have different names for the reference “twin” building.
- Florida’s Code:	*Baseline building*
- MEC/IECC:		*Standard design*

## The “Twin” Building

- Same areas as the proposed building.
- Same geometry as the proposed building.
- Same orientation as the proposed building.
- Same levels of service as the proposed building.

**As compared to what?**

## The Equal Service Principle

- Codes disregard lifestyle choices, so equivalent “levels of energy service” are assumed in both the proposed and the reference “twin” buildings.
- Example:  The “level of service” for air conditioning is the thermostat setting.

**Buildings versus Lifestyle**

## Florida’s Energy Code

- 20 years old (or “in the making”).
- More than 90% choose performance-based compliance approach.
- “Portfolio” compliance is achieved – “on average” Florida homes comply.
- State of Florida provides the compliance tools (i.e. software).

## California Code Experience

- More than 90% select performance-based compliance approach.
- Private vendors provide compliance software tools.
- Critical and necessary to provide detailed procedures for the verification of code compliance software tools(California ACM – 384 pages).

## Other Lessons

- Other compliance approaches must stem from the performance-based approach.
- Must have sufficient “rules” to construct an _**unambiguous**_ ***reference***.
***Reference**** – “... *constituting a standard for measuring or constructing.”					   *Webster’s Dictionary*

## Chapter 4 vs. Chapter 5

- IECC Chapter 4: performance-based approach
- Specifies the energy budget using “rules” for each component of the reference “twin” home.
- IECC Chapter 5: prescriptive approach
- Specifies the minimum energy performance requirement for each component of the proposed home.

**Are they equivalent?**

## Example:  Chapter 5, IECC

-    Windows and doors are included in calculation of wall requirements.
- 	**U****w****=(A****o*****U****o****-A****g*****U****g****-A****f*****U****f ****-A****d*****U****d****)/A****w**

**Where the reference failed**

- where the subscripts designate:
- 	w = wall		o = overall
- 	g = glass		f  = frame
- 	d = door

## The Window Problem

- Chapter 5 includes windows and doors in  overall wall U-value calculation, but ...
- Window U-value are not very important in hot climates.
- Window heat gain is not considered in calculation but is very important in hot climates.
- Outcome from calculation is dependent on building geometry.
- The result is a reference home anomaly.

**Windows are not the same as walls**

## An Exercise in Futility

- Create a group of square buildings of various floor areas.
- Set window area to 15% of floor area.
- Set window U-value to 0.90 (reasonable for Orlando, FL, with 733 HDD)
- Solve the Chapter 5 equation to determine the required wall R-value for each building size.

**IECC Chapter 5 wall U****o**** equation**

## The Window Anomaly!

**Square homes of different floor areas**

**Window U-value = 0.9**
**Orlando HDD = 733**

**Window-to-floor**
**area percent = 15%**

**2100 ft****2**

**2200 ft****2**

**3000 ft****2**

**1000 ft****2**

## Another Lesson

-    Code compliance software tools should be “certified” (re: California experience).
- Certification” should ensure that homes that should not comply, do not comply.
- At a minimum, certification procedures should evaluate software tools for the following:
- Reference home configuration ability
- Load prediction ability
- System performance prediction ability, and
- Code compliance determination ability.

## One More!

-     Procedures for developing “trade-off” compliance approaches should be codified.
- Local jurisdictions should be able provide their own compliance approaches.
- Anyone can determine if a given approach complies with the performance requirement – the principle of full, public disclosure.

## Code Myth No. 1

- “Builder’s prefer prescriptive energy codes.”
- Above all, builders value the flexibility to satisfy their customer.
- Where good compliance tools are available, the performance-based approach is preferred by a 9 to 1 ratio.

## Code Myth No. 2

- “Performance-based codes are too difficult to enforce.”
- Code officials don’t have to understand the intricacies – that’s the purpose of good software tools.
- A “custom prescription” can easily be reported for each home.  With this, the code official can easily determine compliance.

## Compliance Summary

## Compliance Detail

## Code Myth No. 3

- “Performance-based codes are too difficult to use.”
- Ease of use is a function of the compliance tools, not the complexity of the method.
- PC-based compliance tools can make virtually all methods equally easy.

## Chapter 4, IECC

- _Remove loopholes_:  “All Standard Design home characteristics not specified by this Chapter shall be the same as in the Proposed Design home.”
- Move minimum component requirements from Chapter 5 (or Chapter 6) to Chapter 4.
- Refine Standard Design rules to avoid ambiguity.

**Recommended Revisions**

## Chapter 5 (and 6), IECC

- Require all compliance pathways to _meet or exceed_ “worst case” performance as defined by Chapter 4.
- Codify verification and certification procedures for code compliance software.
- Codify allowable methods to determine customized prescriptive and trade-off compliance pathways at local levels.

**Recommended Revisions**

- Thankyou!