ERV vs. HRV...

ER/HR ventilators

Both er/hr ventilators are a box with a fan in it.  The differences are in the core or element that is inside, that the air passes thru.  Some include filters for particles and UV lights to inhibit bioaerosols, but the energy transfer occurs in the core.  The hr ventilator has a metal core.  The incoming air passes on one side, and the outgoing air on the other.  Since heat always moves to cold, the energy gets transferred to the incoming air in the winter, and the outgoing air in the summer.  Only sensible heat is effected in an HR ventilator.  In winter, frost may form on the element, and would soon clog it if there wasn't some provision for melting it, usually circulating warmer inside air around it, causing the frost to melt.  In summer, condensation will occur, and these two sources of liquid water are the reason an HR ventilator always needs a drain, and must be located in a space that does not go below freezing.  They tend to dry a space.

An Energy recovery ventilator uses a different element.  It may be a hygroscopic paper core, which will transfer moisture as well as heat from the higher side to the lower.  The ER ventilator never has liquid water, and recovers both sensible and latent heat.  It does not requirea drain, and tends to balance humidity.

Both run at about 80% efficiency, and can be controlled by a manual switch, a de-humidistat or  a program from some better quality thermostats that have a ventilation feature.  Usually, these units run 24/7 on low speed, but can be sent to high speed if needed for more fresh air, for example, when you have lots of guests.  They also tend to dilute and exhaust pollutants and odors.