Mini-split, air circulation and noise transmission
We are considering using a mini-split system on our new tight home (double wall cellulose on a insulated slab) in Upstate NY (Zone 5a). We are both consultants with full time home offices.
One option is a hidden short ducted system on the first floor (1,500 sf) to duct air to the main living area and the master bedroom area and a regular mini-split unit for the upstairs (800 sf) where we will have our two offices, a bath, storage and a guest room. Our mechanical room is on the second floor. I don’t want a visible unit on the first floor.
I don’t mind a visible unit on the second floor but I am concerned about comfort in our offices given that we will want to keep the office doors shut because we are often on the phone at the same time. Any openings (jump ducts or undercutting the solid doors) that will let the air circulate will also allow noise to transmit.
Any thoughts on a cost effective solution that provides comfort and keeps the noise out. We also will have a HRV or ERV and a wood stove with an outside air supply. The floor plan is attached.
Thank you.
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Have you thought of contacting an architect with green building experience? In my area we have at least one. The reason I suggest this is if you learn here a little, you still need installation experience along with all the other phases of construction needing coordination and experience and successful past outcomes.
Who are you buying from? Who is installing? Who is maintaining? If you know these answers then you should be able to answer your posted question.
I am working with a builder that has green building experience and who is recommending a mini-split system as one option because it provides both heating and cooling in one system. The noise issue is unique since noise control is not usually an issue in a residence.
I want to see if anyone at GBA had dealt with noise control in designing the HVAC system in a tight home.
it is my understanding jumper ducts (through the ceiling, not through the wall) greatly reduce sound travel. We use this design often on schools (from classrooms to halls for example) without issue or noise complaints. With your plan, I would guess you could have a jumper duct from one office into the hall. Air circulation can be aided with the HRV and ceiling fans.
Elizabeth:
Here are a couple of options that I have specified for past for clients with a similar set up to yours.
1. DUCTED OPTION: Assuming you have an encapsulated attic, you could use another ducted unit serve the second floor, install the Tamrack Return Air Pathways (RAP), instead of jumper ducts, to get return from each room to a central return grill in the central hall ceiling. In a tight, well-insulated home, 800 s.f. will likely have a max load around 6-7,500 btu/h. The smallest ducted fan coil is 9,000 btu/h and would serve this area well (it's OK to be oversized with mini-splits).
2. DUCTLESS OPTION: Install ductless unit (wall-mounted, floor mounted, ceiling cassette) in one room and use an Air Share Fan (http://www.tjernlund.com/airshare_ventilation.htm) to push air in to the adjacent rooms. I would recommend the RAP, again, as it has very good sound and light control, with less material. Building America did a study on their effectiveness, and showed some pretty good results. http://www.ba-pirc.org/casestud/return_air/index.htm
p.s. the floor mounted unit is probably the only ductless unit that can be recessed in to a wall cavity and "hidden" with a decorative grille with enough free air flow.
great info Chris. About how much do one of those transfer fans run do you know?
Thanks Chris,
Sounds like some good solutions. I am thinking we could also use the Air Share fan to get the warm air from the wood stove around when we are using the stove. Does the air share use much energy?
Jesse: I've seen them run anywhere from $100 - $200. Amazon sells them for about $130
http://www.amazon.com/Tjernlund-AireShare-Room-To-Room-Ventilator-Hardwired/dp/B000UC7ACE
Elizabeth: The fans are rated at about 25 watts, or .5 Amps. That's about the same or less as the fan in the indoor units of the mini split systems.
Here is their spec sheet: http://www.tjernlund.com/Tjernlund%20_AS1_AS1P_AireShare_Spec_Sheet_8513030.pdf
Chris, love your post. Any of us that have not used a mini split need to know how to and how not to, set them up.