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Mechanical Ventilation is not being optimized - BEopt

asked 2020-11-18 23:59:23 -0500

EnergyModeller's avatar

updated 2020-11-19 12:57:19 -0500


I am developing a retrofit strategy for poorly built homes from 1960s to be Passive House ready. I have developed a series of assemblies (Figure 1) to be optimized in my house (Figure 2). However when I run my simulation the mechanical ventilation always sticks at "none" regardless of the price the efficiency and energy consumption. I have even tried dropping the price to $0 for equipment and made the HRV/ERV super energy efficient while still having a high SRE. Figure 3 is the inputs I currently have for my BEopt Model. Please let me know what you think.


image description Figure 1: Optimization Levels

image description Figure 2: Geometry

image description image description Figure 3: Imputs

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answered 2020-11-19 09:31:17 -0500

updated 2021-04-12 13:00:34 -0500

Whole house continuous mechanical ventilation nearly always result in higher energy use than having no such system. After all, you are bringing in outdoor air that needs to be conditioned to the thermostat setpoint (plus using fan energy to do it). Mechanical ventilation systems are designed to improve indoor air quality, not save energy. Even systems with heat recovery will result in higher energy use than no system, though not as high as systems without heat recovery.

In general, it only makes sense to optimize across mechanical ventilation systems that provide the same level of indoor air quality. In your example above, that would mean deselecting the None option, so that the optimization is evaluating different HRVs/ERVs that all provide the same amount of airflow (100% of ASHRAE 2010 requirement).

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answered 2021-04-11 09:13:04 -0500

jpierce's avatar

updated 2021-04-12 12:59:04 -0500

Rather than including "None" in your options try using "Exhaust only". While older homes will likely lack the automated controls that trigger bath fans to run, this scenario is something that the optimizing engine can reasonably trade-off versus low infiltration + HRV/ERV.

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Asked: 2020-11-18 23:59:23 -0500

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Last updated: Apr 12 '21