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Guide for Selecting an Independent AC Unit for Home or Office

written by: Raunekk • edited by: Lamar Stonecypher • updated: 3/7/2009

Why to choose an independent AC unit? What are the pros and cons of an independent unit? It is important that we take into consideration the answers to such questions before we take a plunge to select an HVAC system.This article will educate us as to why and when to choose an independent AC unit.

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    It is important to have an impeccable understanding of the types of AC units available in the market when you are selecting one for your requirement. This is necessary because many advantages and disadvantages will follow after installing a unit and thus it is necessary to understand as to where to compromise depending on the requirement. An independent unit is mainly selected keeping in mind factors such as room capacity and energy consumption.

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    Advantages and disadvantages

    A unitary or an independent AC system provides cooling to only a particular zone and is not connected with rest of the spaces. Thus if there is a malfunction in a unit, only a particular temperature zone will be affected.This is one of the biggest advantage of selecting an independent AC unit. But it is also seen that most of the unitary systems do not provide close humidity control. Though such type of application of humidity control is not often required, except in computer room applications, it can be acquired using special purpose packaged unit according to the requirement. A disadvantage of a unitary system is that it produces undesirable operating sound and also the appearance is often unappealing. The air filtration system that is provided in the unit is often not efficient and an addtional outside air economizer will not be economical at all for a low cost cooling. A proper condensate removal arrangement is imperative to prevent spoiling of the conditioned space and also is an integral part of the whole system.

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    Airflow and temperature control.

    The temperature and airflow control in a unitary system are often limited. Initially all the independent units used to come with only two position temperature control, though they have now been substituted by digital controls. But still the temperature control remains a bit limited. Also the air flow quantity is fixed by design, restricting efficient circulation of air. Thus a unit should be so selected as to cover the entire room capacity with efficient cooling. Also the average temperature and the fluctuation in the temperature of the surrounding area should also be kept in mind while choosing the capacity of the unit. Ventilation air is also fixed by design and operates only when the conditioner operates. So even if the temperature control is inexpensive and simpler, proper selection of the unit is necessary to prevent overloading of the unit and excessive energy consumption.

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    Manufacturer’s assembled units and the ease of installation.

    There are a number of manufacturers producing AC units which are there in the market. It is always advisable to purchase an AC unit from a branded manufacturer who also gives warranty. A branded unit will provide improved quality control and reliability. It is to be noted that the average life of an independent system will be shorter (10-15 years) as compared to a central unit (20-25 years). Installing an independent unit is always easy and the manufacturers also provide easy installation manuals and technicians for the process. The only thing that has to be kept in mind and predetermined is the design of the room and the position where the unit will be fitted, so as to make the installation task less complicated.

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    Cost and energy efficiency

    The installation and initial costs of a unitary system is usually less than those borne by central system. But the operating costs are usually higher in a unitary system. One more disadvantage is that the energy efficiency is low. A unitary unit should be chosen only if the size of the zone is small. But this loss of energy can be saved manually by turning off the units serving unoccupied spaces thus keeping the occupied spaces unaffected. Thus the AC system should be chosen keeping in mind factors such as output efficiency and the costs to be endured.

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    HVAC fundamentals by Samuel C. Sugarman