Tips on Selecting a Ductless Minisplit
Green builders focus on getting high-performance windows and above-code levels of insulation to reduce air leaks in their homes thus most greenhouses have low cooling and heating loads. Besides just the high-performing windows and a good degree of insulation most of the green homes are being heated and cooled using ductless mini splits or ducted mini splits which are air-source heat pumps that have ratings of between 9,000-15000 Btu/h range which are suitable for small load houses. These systems use electricity thus they are a good fit for any home that has a roof-mounted photovoltaic system.
Despite the benefits that these mini splits offer some builders have some doubts regarding them and they wonder if it is possible to cool and heat a house with just one or two ductless mini splits and if extra rooms like the bedroom need a separate heater or forced heat register.
When selecting a mini-split, the first thing to look at is the load calculation of both heating and cooling which can be done using a formula that most contractors do not know and most contractors use the rule of thumbs which can lead to excessive cooling and heating loads and oversized equipment. To get a good mini-split system the person needs to get an overview of the available equipment such as the outdoor unit of the mini split system which is called the compressor and there are many kinds of indoors units among which one is the wall mounted unit that is designed for ceiling installation and is at times called a cassette.
There are various types of ducted indoor units such as a multi-split system that includes an outdoor unit that is connected to either one or more indoor units and most of these units are multi-zone systems not single-zone systems but both mini split and multi-split systems need 220 or 240 volt AC power. Minisplit systems are designed such that as the outdoor temperature drops both the heating capacity and the coefficient of performance (COP) of the air-source also drops thus if the person expected to heat the house with a mini split system when the temperature outside drops to -130F 0r 150F then they will have to look at the heating capacity of the equipment at these outdoor temperatures.
A known truth is that an electric resistance heater has a coefficient of performance (COP) of 1 which means that it is 100% efficient thus when you put in 1 energy unit it gives the user 1 unit of heat and compared annually an air-source heat pump is about two or three times more efficient than an electric resistance heater thus has an average COP of 2 and 3.
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