Exhaust does not stop changing when it leaves an engine. Reactions in the atmosphere can produce new particles and alter the chemistry of existing ones. In laboratory experiments, aircraft-combustor emissions became substantially more reactive as researchers simulated days of exposure to atmospheric oxidants.

Their oxidative potential per unit particle mass increased six- to sevenfold after aging equivalent to approximately 12 days. Emissions from a marine diesel engine showed a different pattern in the same chemical test. The contrast suggests that freshly emitted exhaust alone cannot describe how particle reactivity develops in the air.

The study, published in Environmental Science Atmospheres, was led by Markus Kalberer’s group at the University of Basel. Alexandre Barth and Battist Utinger were its two first authors. The work examined chemical indicators associated with potential harm, rather than measuring disease or demonstrating a corresponding increase in human toxicity.

Disclosure: I work with MENRED, an HVAC ventilation manufacturer. I’m sharing a practical ERV selection checklist for discussion; the linked article is company-affiliated.

A high heat-recovery rating can be useful, but it does not tell you how much energy the building will save over a year. The result also depends on the unit’s airflow and pressure conditions, leakage, fan power, climate, controls, maintenance and the HVAC equipment.

When reviewing an ERV proposal, I’d check:

• What does the rating measure: sensible, latent or total recovery?
• What test standard and operating conditions were used?
• Is the figure gross or net, and is leakage performance available?
• What fan power and pressure drop apply at the design airflow and external static pressure?
• How will supply and exhaust airflows be balanced after installation?
• Does the energy comparison include the fans, frost protection and affected HVAC equipment?
• Are bypass, defrost and filter maintenance appropriate for the project?

The comparison should keep the required ventilation rate and indoor air quality target consistent. Otherwise, apparent savings could come from providing less ventilation.

For engineers, designers and commissioning teams: which data point is most often missing from ERV proposals?

Full checklist:
https://www.menred-hvac.com/newsdetail/erv-efficiency-vs-real-energy-savings-what-buyers-should-check

City council has long sought to dismantle the citizens idling complaint program and allow idling again in the city for the sake of big business. Intro 561-A is their latest attempt. Please sign the petition and tell Speaker Menin that NYC deserves clean air!