July 31, 2015
Over the last 15 years, energy use in new homes has been reduced by nearly 40%. Voluntary, market-driven programs like ENERGY STAR®, Built Green and R-2000 have provided builders with the technology and construction practices needed to build more comfortable, healthy and efficient homes.
Today, we have building codes that require increased insulation values, mechanical efficiencies and air tightness. In many provinces a new home built today delivers the energy performance of R-2000 homes built in the early 2000's.
One very direct consequence of these changes is that heating and cooling loads have dropped substantially in new homes across Canada.
However, the national standard for appropriately evaluating the heat loss/heat gain of a Part 9 building (CSA F280-M90) has remained largely unchanged for nearly 20 years!
This can, and does, cause problems for builders.
An unintended consequence of using the old CSAF280-M90 standard when designing HVAC systems for today's new homes is chronic over-sizing of heating and cooling equipment, as well as oversizing of air duct delivery systems.
Within the industry it's well know that oversized systems in new energy efficient homes often result in comfort issues for occupants, and can lead to homebuyer complaints and warranty claims. Somewhat like putting shoes on a child that are to big, large oversized HVAC systems result in homes that run "sloppily" and inefficiently.
Depending on a home's layout, short-cycling of HVAC equipment can lead to cold rooms on the second floor, and in rooms over garages with exposed floors. During the cooling season, the problems change, but include poor thermal circulation and inadequate dehumidification.
Short cycling also results in decreased mechanical efficiency, and compromises the performance capacity of today's more efficient heating and cooling equipment.
These problems can be avoided by the use of the new CSA F280-2012 standard. Some designers/contractors will also recognize some cost savings while optimizing system designs under the new standard.
The new CAN/CSA F280-2012 Standard "Determining the Required Capacity of Residential Space Heating and Cooling Appliances" is a freshly updated standard. It provides a tremendous opportunity for homebuilders and the HVAC industry to rationalize new mechanical system design.
Here is a brief synopsis of the more critical changes.
In applying the new Standard, designers and mechanical contractors will need to recalibrate old "rules of thumb" for sizing equipment in today's new homes:
In the last 2 years the new Standard has been applied on multiple Net Zero projects across Canada with great success. Occupants of these Net Zero, ultra efficient homes are raving about the "comfort" of their homes. Beside being quieter, and often smaller, 'right sized' equipment delivers ambient temperatures which are nearly identical on every floor and in every room. The mechanical systems also operate at peak efficiency further reducing the cost of operation.
The new CSA F280 Standard results in more accurate and potentially lower load calculations that reflect the efficiency improvements in today's new homes.
Here are results applying both the old and new standard to a reference home assumed to have an HRV, air tightness of approx. 2.5ACH50, January design temp of -20C, and summer design temp of 31C.
|Total Heat Loss
|Air leakage component of Heat Loss BTUs/hr||Total Heat Gain
|Current CSA F280||57,646||13,685||32,450|
|New CSA F280||34,665||5,049||26,750|
By Andy Oding, Senior Building Science Associate