Add AC to ERV Ductwork?
pico_project
| Posted in General Questions on
Northern Michigan, 1,600 sq/ft single story ranch.
We have a boiler for heating and currently no cooling.
As part of our remodel we had an ERV installed with new ducts ran throughout the house. The plan at the time of the remodel was to add mini splits for cooling in the next few years.
We’re now started to plan for mini splits, their location, etc… and was wondering if connecting a ducted AC unit to the existing ERV duct work would be a better approach?
We’re mainly looking to just take a little edge off on 85F+ days. Ideally maintaining a temperature around 75F.
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Replies
The air flow rates for ERVs and air conditioning are very different. You would get some cooling through the ERV ductwork but it would be inefficient due to the ductwork sizes being too small.
Thank you for the reply. What size duct are we talking about? I do run my ERV very high most of the time. The ducts are 8" on the main intake and exhaust. Then it's at least 6" duct to all locations. I know it's 6" oval duct in the wall — not certain about the branches in the crawlspace — but at least 6".
Duct design should follow ASHRAE Manual D, and depends on many factors--there's no way to know whether 6" or 8" will be enough without doing a full analysis of your house including heating and cooling loads, room sizes and configuration because every bend or fitting affects airflow rates.
The high velocity AC use smaller ducts, so if calculations show that central AC needs larger ducts than what you have, that may be an option to consider.
Can you get the specs/design for your ERV (ducts diameter may be shown on the plans)?
The thing about high velocity is that it is noisier.
Pls consider that AC needs to move the air around the building (recirculate) with the coil somewhere in the loop, a ERV is straight in and out. You would need to use the ERV ducts in a recirculationg mode primarily as AC and inject the fresh air from the ERV in front of the fan to the duct. This is a redesign of the whole setup, nearly guaranteed to need a major rework!
I might suggest a air to water heat pump with a chilled water coil in the ERV supply ductwork and a buffer tank. This will make matching the capacity and flow requirements not as big of deal. But won't be cheap. You would need some additional fan coils to handle the load of the building though.
If you cool the air down to 10-12degC it should take the edge of the humidity.
The other option would be to configure the ERV to dump into the a ducted minisplit return air plenum to take advantage of the mini split conditioning and distribute via the upsized minisplit ductwork.
See my comment here:
https://www.greenbuildingadvisor.com/question/why-not-minisplit-inline-with-erv-ducting
It can work but won't get 100% of cooling through it but it will definitely take the edge off. The air handler needs to be rated for similar pressure as your ERV, so it can't be a low static unit.