Many heating and cooling (HVAC) systems are sized by some rule of thumb, and “to be on the safe side” end up significantly over sized. While this may protect the designer and installer from receiving calls that the home is not getting warm, there are significant downsides to this practice.
- Equipment unlikely to operate at its design efficiency resulting in higher operating cost
- System cycling often resulting in temperature swings and reduced comfort
- Increased stress risking premature component failures and reduced service life of the equipment
- Added cost to purchase and install the over sized equipment
At BrightSense, with help from detailed science based simulations, we carefully quantify the actual heating and cooling loads, and put them into perspective with the local climate, orientation of the structure, and other site specific factors. In many cases we manage to cut loads initially suggested by traditional tools like Manual J by up to 50% resulting in significant savings all around.
The design day temperature, which is the typical low temperature for the year at a particular location, rarely occurs for more than a few hours at a time. Sizing equipment for these conditions is not prudent, in particular for super-insulated homes that are designed to coast through extreme weather without noticeable effect on indoor comfort.
Smaller equipment not only costs less, it also allows reducing the size of the distribution system saving even more. Smaller ducts require less space and offer more flexibility for the installer. During operation, a smaller system requires less energy to run, less air to be circulated, further reducing noise and draft.
Right-sizing or under certain circumstances under sizing the main HVAC equipment has many advantages.
- Longer run times with equipment reaching and staying at peak operating efficiencies for extended time
- More consistent operation providing high level of comfort
- Appliances operating as designed by the manufacturer
- System, installation, and operational expenses only for what is really needed
Only after the actual loads are known can a serious discussion about type and size of equipment be had.
Hans Joachim Preiss
Office: +1 720.500.5470