Efficient Heating with Minisplit Heat Pumps: Page 3 of 4

Intermediate

Inside this Article

Outdoor portion of mini-split heat pump.
Indoor portion of mini-split heat pump.
This wall-mounted indoor air handler is equipped with a pump that is used when the condensate cannot drain by gravity.
A ceiling-mounted indoor air handler can be slightly less efficient, but is less obtrusive than a wall-mounted unit.
A stand-mounted outdoor unit, raised above typical snow levels. The cap prevents snowmelt from accumulating on the coil.
A floor-mounted indoor air handler looks like a space heater, but with heat-pump efficiency.
A wall-mounted outdoor heat pump allows placement flexibility and simplifies installation. Care should be taken to avoid installing outdoor units near bedroom windows.
Air filters help improve indoor air quality. They are easy to remove and clean with soap and water or a soft vacuum brush.
Heat pump controls can be on-the-unit or wall-mounted thermostats, handheld remote controls, or smartphone apps.

While multizone units suffer some efficiency challenges relative to single-zone units in climates with long stretches of freezing weather, they can also have significant benefits. In homes with lots of smaller rooms that are heated and cooled with electricity, having numerous outdoor units scattered along the exterior of the home can be unsightly. In addition, some single-zone units may be oversized for the heating demands of a small room. With careful planning, these small rooms can be served by a single outdoor unit to provide the same level of comfort with less equipment, less visual impact, and less cost.

MSHP production during cold temperatures can be improved by selecting a model that utilizes a pan heater to reduce the unit’s defrost cycling. During a defrost cycle, the unit extracts heat from inside the home to melt any frost that has accumulated on the outdoor unit’s heat exchanger. The pan heater is an electric resistance heater that reduces the accumulation of frost on the outdoor unit and minimizes these cycles (see “Defrost Cycle” sidebar). These models can be rated for outdoor temperatures as low as -15°F. As might be expected, this feature requires more electricity than for a unit without the pan heater.

Common Features

In addition to heating and cooling modes, MSHPs  commonly have a dehumidification mode and a fan mode. Dehumidification mode is similar to cooling mode—the unit removes moisture from the air, which condenses on the indoor heat exchanger and is drained to the outside. Dehumidification mode is less precise than cooling mode, in that it runs at a low fan speed to constantly cycle the air through the unit and a cooling capacity that is a fraction of the unit’s maximum output.

The fan mode can be used to cycle the air in the room through the unit to provide a more even distribution of temperature in the room, without turning on the heat pump. This may help distribute heat from a wood heater in the winter, for example, or simply provide more comfortable air movement in the summer.

The indoor unit also contains filters that limit the amount of dust and other airborne contaminants that accumulate on the heat exchanger, and help purify the air. These filters need to be cleaned regularly and are easily vacuumed with a soft-brush attachment or rinsed with tap water. The filters may need to be cleaned only every few months in homes with good air quality. In homes with smokers, where candles are used regularly, or that have airborne contaminants like pet hair, the removable filters need to be cleaned more frequently. If they are not cleaned, the airflow will be reduced, reducing the heat output.

Comments (5)

Greg Smith_0_0's picture

Mini splits are a much better option on the backup panel than a central HVAC unit. I always cringe when someone send me a load profile with a 5T AC unit, or two... You can get so much more bang for your buck from your storage system if you are smart about what loads you run when the grid goes down.
"But Greg, I GOTTA HAVE MY KOI POND PUMP AND MY GLASS KILN ON THE BACKUP PANEL!!!"

Marc Fontana's picture

Thanks for the article . A few questions : What is the average cost for a small 1-zone unit? Do they require a 240v circuit ? What maintenance is there on the outdoor unit ? Can installing a MSHP system be a DYI project ?

vwoodruff@insourcerenewables.com's picture

Marc, the average cost for the equipment for a single-zone mini-split heat pump is around $2k. The cost including labor typically is in the $2,500-4,000 range depending upon the size of the unit and the difficulty of the installation. Though there are 120V models, their performance tends to be dwarfed by the 240V models. Maintenance on the outdoor unit includes cleaning the coil periodically - annually clearing leaf debris, for instance, and a low pressure coil cleaning wash every few years. With the high performing units, it is highly recommended to have a refrigeration professional perform at least that portion of the installation. The greenhouse gas potential from losing refrigerant from these units is not to be ignored.

Ronald Gilliland's picture

Has anyone measured the power draw on their mini-split even when the unit is powered off? I have a Fujitsu Halcyon 9RLS3 and have found that there is a continuous draw of 100 watts after using the control panel to fully power the unit off. That seems a shockingly high power draw for a device intended to be highly efficient. During months when in Pennsylvania climate when there is no need to use the unit this parasitic load adds up to a large power usage. I now keep the breaker off to avoid this except for the times when need for unit is clear.

Vince Caruso's picture

Nice article. Some comments on instalation could include self install units now available, some may be moved to new home or other rooms many times as they have valves in the precharged hose's connectors. Just screw them on and turn on the valve. This could be a real cost savings for DIY'er. Great technology for solar powered homes.

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