Almost all packaged A/C or split system units do not have a service factor for extra capacity. Even when new, these units may not yield the cooling BTUH capacity specified due to improper installation and/or incorrect load calculations at the inception of installation and startup. Consequently, as the system gets older and parts become less efficient, the system may lower its capacity to the point...
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There are many existing systems that require the addition of cooling to a heating-only unit. Systems need to keep pace with changing requirements for spaces that include a mandatory requirement for cooling. Existing systems can already have cooling, but a booster will have to be placed into the system to add additional cooling. When cooling is added, it must be decided whether the tonnage can be...
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Most HVAC steam heating coils operate with steam pressure below 25 PSIG, and a very large percentage are below 15 PSIG. These coils have specific piping and coil arrangement requirements to allow these systems to optimize performance and avoid systematic problems that require premature replacement. Preheat coils in most of the country will require an arrangement that deals with below freezing air temperatures. In conjunction with...
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Operating water coils that are prone to air temperatures below freezing normally need the use of anti-freeze. The most common is glycol. This has been used for over 40 years, and there are two common types, ethylene and propylene. Anti-freeze provides a safeguard if there are mechanical or electrical breakdowns that may cause fluid to sit in a coil with below freezing air going across...
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Finned tube coils are meant to have contact with the air flow, as more contact creates more heat transfer. Heat transfer is nothing more than heat exchanged from one medium to another, and the goal is to create maximum heat transfer efficiency. The downside to this process is the coil’s susceptibility to foreign materials becoming lodged in them. The following explores this problem in a...
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Many projects require downstream duct mounted coils to heat or cool air to its final desired temperature. Normally there are upstream coils that regulate the leaving air temperature to a design intermediate level. The duct coil takes the air from that intermediate level to its final desired temperature. Many systems can vary the air flow or water volume to achieve a desired leaving air temperature...
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HVAC and process heating/cooling must deal with the added tonnage created by using fresh air from outside. Most times, the requirement for fresh air is mandatory and can go from 10% all the way to 100 % of the system air flow. There are numerous rules and regulations written to eliminate air flow quality problems, including bacteria and other micro-organisms, that can cause health problems....
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There are many reasons why hot water coils in your system can under-perform. Some reasons are from the time of the design, and many other instances can also occur after the coils have been installed. Here are 10 common reasons why hot water heating coils can fail: Air stratification issues - The air flow across the surface of the coil is not being evenly...
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Most heating coils are either a preheat or reheat coil mounted in a unit. Also, reheat coils can be mounted downstream of a unit in a supply duct. This article will address hot water and steam heating coils. There are numerous reasons why a heating coil may not perform to its expected capacity. The following are the major ones. Improper Coil Selection Heating coils can be selected...
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