HVAC design, ducts & performance

Heating and Cooling Design

After the design of the building envelope, HVAC design can have the biggest impact on energy performance. There are a few basic decisions have a enormous effect on energy use: 

​​>  The air handler is inside the envelope...many times it is in the attic or garage where it loses heating and cooling to extreme temperatures.​​

>  The ducts are inside the envelope.

>  The high insulation and air sealing levels in this building translates into a lower heating and cooling load. Dropping the load means smaller equipment.  The original design included a 3 ton system.  With the insulation we were able to install a 2 ton unit...a 30% drop in size!

Duct Sealing and the Duct Leakage Rate

Energy Star reports that for any given house "about 20 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts. The result is higher utility bills and difficulty keeping the house comfortable, no matter how the thermostat is set".  

Reducing the duct leakage rate is a crucial part of 311 Varnum's energy model.  In fact, as part of the LEED criteria, the duct leakage rate measured by an independent third party tester to ensure it meets the LEED criteria. Energy Star puts typical duct leakage in the ballpark of 20%.  Our goal for 311 Varnum was under 4%.

Our final leakage rate is will be determined by upcoming testing...We'll keep you posted!

HVAC Equipment Performance

311 Varnum has a 15 SEER/9.0 HSPF high efficiency heat pump system. ​

Seasonal Energy Efficiency Ratio (SEER):

SEER indicates the relative amount of energy needed to provide a specific cooling output. The higher the SEER, the more efficient the equipment.   Many older systems have SEER ratings of 6 or less. However, the minimum SEER allowed today is 13. 411 Varnum's HVAC equipment is 15 SEER, which is 20% more efficient than the minimum required 13 SEER.

Heating Seasonal Performance Factor (HSPF):

HSPF is specifically used to measure the efficiency of air source heat pumps. It is the ratio of heat output to electrical power for a season.  The most efficient heat pumps have an HSPF between 8-10.  311 Varnum's HSPF is 9.0.

Not sexy, but very important!