Efficient Heating with Minisplit Heat Pumps: Page 4 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.

Controls

The indoor unit functions are controlled by a wireless remote, a wired control, or through a wireless network to provide local or distance control with a smartphone app. Unlike standard heating systems that use a room thermostat to tell the unit when to turn on and off, MSHPs measure the room’s air temperature with a sensor at the indoor unit’s air intake. Another sensor in the indoor unit measures the temperature of the conditioned output. These temperatures determine how the indoor unit is run and are compared to temperatures measured by the outdoor unit to determine the speeds of the compressor and fans. Even when there is no heating or cooling demand, the indoor fan runs at its lowest speed to monitor the room temperature, unless turned off entirely.

Additional Features

Some indoor units have occupancy sensors (i.e., motion sensors) that can reduce temperature when there is no movement in the room, modifying its target temperature by up to 8°F to save energy. For example, if the control is set at 70°F and there is no movement in the room for 20 minutes, the unit will gradually adjust its target heating temperature to 62°F until someone enters the room. At that point, the unit ramps up to 100% of its output to increase the room temperature.

Some units provide timer programming similar to a programmable thermostat. Other features may include:

  • A sweep function that directs the airflow out of the unit up and down and left to right, similar to the behavior of an oscillating fan, to more evenly distribute heat.
  • For homeowners bothered by the outdoor fan, a mode that reduces the capacity of the MSHP, thereby decreasing the amount of noise made by the outdoor unit.
  • An infrared sensor that can sense areas of a room that are hotter or colder than others and can redirect the airflow to provide consistent comfort.

These features may drive the selection of a unit for a particular installation. For example, if an indoor unit is placed on the longer wall in a narrow room, the automated sweep function or infrared sensor may significantly improve the room’s heat distribution.

Determining the best MSHP for your application depends upon several factors. Heating and cooling loads will determine capacity and whether you need a cold climate unit with a pan heater. The layout of the home and your heating zones will dictate how many indoor units are needed. The layout and available space for the indoor units in each room; the installation details needed to connect the indoor unit to the outdoor unit; and aesthetic preferences may influence the type of indoor unit you choose.

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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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