Using a minisplit system?

[FiltrationEngineer]

I'm conisdering replacing a roof mounted residential package unit with a tri-zone minisplit AC/heat pump. The existing ductwork does get to all areas of the house and it looks like the minisplit is more efficient (15 SEER).

The home is a vacation rental and lots of time the upstairs isn't used because a couple stays there, so the systems upstairs wouldn't be used when not needed.

Is Friedrich a reputable manufacuter?

Is there any reason why I shouldn't use the minisplit?

Any commnents are appreciated.

 

[ChrisConley]

No reason not to use a minisplit other than cost, they are usually pricier than a residential packaged unit. Easier to zone though, and as you say the efficiency is higher.

One major issue would be ventilation. It needs to be dealt with somehow as well.

 

[FiltrationEngineer]

Thanks for the reply.

By ventilation, you mean getting enough air moving around the room?

 

[ChrisConley]

Nope, I mean outdoor air being brought into the space. This is required to replace the air being exhausted from washrooms/kitchen, as well as dilute indoor contaminents. Check your residential codes for how much air needs to be brought in and how.

An HRV or ERV exhausting from the washrooms and returning into the space is a good idea.

 

[ChrisConley]

Why Ventilate your Home,

Paraphrased from Rob Dumont:

Every house needs ventilation. Most older houses get their ventilation from air leakage, but most modern houses on the are now tight enough that a mechanical ventilation system is needed.

Why do houses need ventilation? Let’s go back to fundamentals.

There are about five main reasons. First, people need about 8 Litres per second (15 cubic feet per minute) of reasonably clean air for health and comfort. We ingest air at about 380 parts per million outdoors and our lungs reject carbon dioxide into the air that we exhale. Our exhaled breath is quite loaded with carbon dioxide, with about 40,000 parts per million or 4% CO2 . If you recycled that exhaled breath directly back into your lungs, you would soon be overcome with carbon dioxide poisoning. This is essentially what happened in the Black Hole of Calcutta, when a large number of people died in a confined space. Inside houses and most buildings, carbon dioxide levels should generally be below about 1000 parts per million. If the level is higher, it is usually a sign of inadequate ventilation (or a blocked chimney.)

A second reason that humans must have ventilation is to get rid of moisture that the body emits. Sedentary adults release about 0.1 kilogram (0.1 litres) of moisture per hour, partly through breathing and partly through skin evaporation. Cooking, bathing, floor washing, etc. all contribute additional moisture to the air. One of the common signs of inadequate ventilation in a home is high humidity, with condensation on the windows.

A third reason for ventilation is to dilute body odour, perfumes, deodorants, cologne, etc.

A fourth reason to ventilate is to remove the offgassing from building materials. Our paints, floor coverings, furniture, cabinets and so on all will all emit some volatile organic compounds, and these should be diluted by adequate ventilation. It is also important to choose building materials carefully to avoid organic compound emissions and formaldehyde.

A fifth reason to ventilate is to ensure that there is adequate combustion air for furnaces, boilers, water heaters, fireplaces, etc. When any fuel burns, sufficient air must be supplied or deadly carbon monoxide can readily occur.

In older houses, leaky walls and ceilings will generally provide enough ventilation air through most of the year. However, when there is no wind and the temperature inside the house is the same as outdoors, there is no driving force for ventilation, and very little air change will result.

 

[lilliput1]

Openable windows are considered sources of ventilation.

 

[HVACHawaii]

Usually operable windows will be suitable to comply with code for OA requirements in most jurisdications. Usually for residential, toilet/kitchen exhaust runs intermittant and it is okay to allow the residence to be negative for that time period, unless it is a very humid climate.

If you want a deluxe system ($$$) 100% outdoor air unit from dectron, desert aire, solution air, etc. would be recommended to pretreat and reheat outside air before it is injected into the conditioned space. Essentially you are separating the sensible and latent cooling, using the splits for the sensible and 100% OA unit for latent.