"An efficient (hvac) system is not merely one that uses efficient equipment. System interactions play a major role in the overall system efficiency. Particularly for systems that serve multiple zones, the efficiency of the air and water distribution systems and how they are controlled can be much more important factors in determining overall hvac system performance than the efficiency of each piece of equipment."
So begins chapter 6 in ASHRAE's newly released (Standard) "90.1 User's Manual." Rather than just announcing a new standard to be implemented, in this case "Energy standard for buildings except low-rise residential buildings," ASHRAE wisely decided to put together a sound compendium of actual examples and helpful hints, charts and graphs for compliance.
This book is as wide-ranging as the standard itself, covering not just hvac - which it addresses in the aforementioned chapter 6 - but also administration, enforcement, building envelope design, water heating, lighting, etc.
In the building envelope section, the widely used but seldom understood mysteries of U-factors and R-values are explained, along with heat capacity. For, as we read in chapter 6, hvac alone does not make for an energy efficient building: "¿ a poorly designed hvac system can easily have twice the yearly energy costs of an energy-conserving design."
Demand controlled ventilation (DCV) is a relatively new concept and is described here for the first time, even to where CO2 sensors should be placed.
Duct insulation and construction are also described, giving a thorough example for a building located in downtown Chicago for specific R values according to placement and type of ductwork: supply and return ducts on exterior of the building; supply and return ducts in unvented attic with roof insulation; exterior wall of return plenum, etc.
The manual describes some of the changes that have been made over prior publications. In the section on mandatory provisions for mechanical equipment efficiency, for example, it states how part-load efficiency limits in 1989 were added for most equipment types, recognizing that most equipment operates at part load most or all of the time. "However, the part-load requirements were not stringent due to the lack of actual product part-load performance data available at the time¿ (since then) the level of stringency has been increased."
The manual has an index as well as a table of contents and definitions, abbreviations and acronyms. Chapter 2 defines the scope of what both the document and the standard attempt to accomplish. As it says, "Although Standard 90.1 is not a code, it is intended to be adopted as a code by governmental agencies that are empowered to enact codes through legislative or regulatory processes."
"For our own good," it might add.
(Contact ASHRAE at 1791 Tullie Circle, N.E., Atlanta, Ga. 30329; phone 404-636-8400; www.ashrae.org.)