Hi All,

Regarding the requirement for energy recovery in high rise residential buildings following ASHRAE 90.1-2010, section 6.5.6.1, I want to analyze the difference between a pressurized corridor system vs. in-suite ERV system, and get your opinions.

My building is in CZ 6A, and following this I would need energy recovery on a fan system if my design were greater than 80% fresh air, and greater than 0 cfm (i.e. any amount), down to greater than 5500 cfm and 30%-40% fresh air, per Table 6.5.6.1.

In a pressurized system, it is certainly feasible that these thresholds will be exceeded due to the high amount of air pumped into the corridors, at 100% OA. However, you can get around this with exception 6.5.6.1h - the largest exhaust source is far less than 75% of the fan system design OA rate. In this case, that would be the central corridor fan, which is serving both the corridors and suites, and the exhaust would be the individual WC fans in suite. Diagnosis - no ERVs needed.

In an in-suite ERV system, again the Table 6.5.6.1 thresholds will likely be exceeded , since any amount of flow will need heat recovery if it is more than 80% fresh air. In this case, each individual ERV is its own fan system, again at 100% OA. The corridor system is compartmentalized from this, and again can be exempt per 6.5.6.1h, as there would be multiple exhaust sources. In suite, however, the ERV supply and exhaust are balanced, and very likely within 75% of each other, so the exemption no longer applies. Diagnosis - ERVs not needed for corridors, but needed for suites. In other words, once an in-suite ERV strategy is designed, you are penalized for it.

However, if you include the terminal fancoil/heat pump flow when considering table 6.5.6.1, the % OA would likely drop below 30%, and therefore heat recovery is no longer needed. Is it appropriate to consider the terminal device flow here - be it either in series or parallel with the ERV?

Your thoughts are appreciated. Are there any other interpretations for this out there?

Adam Barker, MBSc, C.E.T., LEED AP BD+C