HVAC retrofit – how to understand comparative performance of different solutions
I would appreciate help understanding how to comparatively evaluate performance effectiveness trade-offs for different HVAC retrofit solutions (in addition to cost which is easy to understand). House currently has 4ton supply only 2 cycle heat pump/fan coil.
HVAC retrofit potential/proposed solutions:
1. Keep current 4t 2 cycle heat pump, and ducting and integrate an HRV to supply per Bruce Manclark to create integrated balanced ventilation. Replace existing spot exhaust fans with Panasonic Whisper Greens with humidistat controls.
2. Install a higher efficiency variable speed heat pump system, integrate an HRV and replace spot fans as in option 1.
3. Install a smaller higher efficiency variable heat pump system, downsize existing supply ducting and reduce the number of supply vents, integrate HRV and replace spot fans.
4. Instead of integrating an HRV to either the existing 2 cycle or new variable forced air, install a fully ducted separate Zehnder HRV system.
We are working to solve an exterior closed soffit moisture problem for our mountain house that was completed in 2014 in climate zone 5B that is also a wildfire and heavy snow area. The house is 3 stories cut into a ridge with the top floor as the main living space (2100 ft2), the bottom floor is storage (650 ft2), and the middle floor is composed of an encapsulated crawlspace (1000 ft2) and occasional use space (380 ft2). Additional house characteristics 1.8 ACH, all ducting is inside conditioned area, flat unvented cold roof with insulation on exterior, high performance walls and glazing. Internal relative humidity measured by psychrometer is over 60% in summer with AC.
Remediation is focused on additional envelope sealing both inside the house and outside the house to stop communication with soffits and HVAC retrofit.
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