<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<font face="Helvetica, Arial, sans-serif">What you describe is what
I have in my own home, and an approach often used. The return is
an open return located someplace sensible (eg, best to have it
draw from a kitchen or bath, but it could be OK to draw from a
mechanical room or basement) and supply to the return duct,
preferably downstream of the grille. <br>
Be careful about door undercuts as air transfer mechanisms: works
great for ventilation, but when you start delivering 100 cfm to a
room, it is rare to have enough of an undercut. Transfer grilles
or jump ducts are generally needed to avoid over pressurizing such
rooms (master bedroom being the most common example).<br>
<br>
The pressure differences caused by the main air handler kicking
in, SHOULD be small if the ductwork is properly designed, but CAN
often be a problem in homes with poor high pressure duct design.<br>
<br>
<br>
<br>
</font>
<div class="moz-signature">Dr John Straube, P.Eng. <br>
<a class="moz-txt-link-abbreviated" href="http://www.BuildingScience.com">www.BuildingScience.com</a></div>
<br>
On 12-03-23 9:21 AM, Alan Abrams wrote:
<blockquote
cite="mid:CADj3_s7OkxMVTZ65HMVBcYz-wze_hdyehSWQj50zhSCc7yRbzA@mail.gmail.com"
type="cite"><br>
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000"><font face="Helvetica,
Arial, sans-serif"> <br>
I guess in general the IDEA of a good HRV ducted into the
return of a modulating heat pump is excellent, exactly
what many people want and need. But the actual products we
have available are far less than perfect and hence other
arrangements are usually less expensive and high
performing.<br>
</font><br>
</div>
</blockquote>
</div>
John-<br>
thanks for the assessment and rules of thumb. with regard to the
diagram, and assuming a NON in line ERV configuration--and if the
building layout makes it feasible--why not use the bathrooms (with
undercut doors or transfer grilles) as full time ERV stale air
returns, with boost mode for showering, and dump the ERV fresh air
either adjacent to main unit return grilles, or directly into the
return trunk line.<br>
<br>
that would seem to accomplish two things--one, to eliminate
auxiliary bath fans, and to recoup the heat--and two, to avoid a
pressure balance issue where the ERV fresh air competes with or
backdrafts when the main system air handler kicks on. Or is the
ERV in the diagram programmed to shut off and dampen when the air
handler is running?<br>
<br>
-AA<br>
</blockquote>
</body>
</html>