Bathroom moisture control in HRV defrost mode
Planning new residential construction in moist and winter cold zone 5A. Basement/walls/roof are R20/40/60, triple-pane, super-tight, well-drying, direct-vent, and mechanicals all in conditioned space. I feel like I have covered most angles, and am looking for extra insurance against mold.
I’m planning for 2 mini-splits to handle 3000sf plus another mini-split for a 600sf in-law, and an HRV to not only provide exhaust/fresh air, but with the help of a few transfer grills, to also distribute heat & cooling throughout the fairly open layout.
Kitchen hood will have makeup air delivered right to the cooktop, with a damper that opens when the hood turns on.
I’m expecting ordinary, distributed humidity to be evacuated by the HRV in winter, condensed by the mini-splits in summer, and also buffered by the dense-packed cellulose, but am concerned about the heavy dosage of moisture from a series of hot showers. I have gone back and forth with the idea of dedicated, exhaust-only bath fans, but I like the idea of balancing pressures with the HRV. I am envisioning flow restrictors in all rooms that the HRV pulls from except the showers, which would instead have a intake like the American Aldes Zone Register Terminal (http://www.americanaldes.com/airflow-zone-controls/zrt-2/) that is wired to the boost switch to open completely and allow increased flow from that bathroom when the HRV is boosted. If both showers are going at the same time then, yes, the flow pulled by the HRV will be even further divided.
Sorry for the long lead-up to this, but here is my primary concern – at the time when I would most want to eliminate concentrated moisture from the house, the HRV could go into defrost mode and dump it right back into the house. Am I doomed to use a pre-heater with this approach?
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