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The Water Cooler
General Discussion
HVAC problem (undersized unit)
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<blockquote data-quote="_CY_" data-source="post: 2776580" data-attributes="member: 7629"><p>when sizing a non-spec build it's better to round up a 1/2 ton vs down. reason is simple .. a bit of headroom for extreme temps can be a good thing. you just don't want to be way off .. like say installing a 5 ton on a 1500sf home. but if you are that close rounding up or down, both will probably work fine. </p><p></p><p>to explain why one constantly sees .. "call a pro" .. HVAC work can get very complex in a hurry. correctly diagnosing what's actually wrong can make a HUGE difference in costs to fix. below goes into a tiny portion of what a competent HVAC tech does ... </p><p></p><p>for instance your example above of variable fan speed and sizing really has little to no relevance. variable speed fans are controlled by newer units with electronic boards. low speed to keep air constantly moving .. medium speed for heater which needs slower air speeds .. high speed if needed to achieve air flow needed to meet AC mfg spec's or what ever ... </p><p></p><p>your AC is spec'd by the factory for XX CFM airflow to keep coils from freezing up. then we get into metering devices .. TXV or piston .. superheat is the amount of heat removed by refrigerant after it passes through A coil or evaporator. a thermal expansion valve will open or close depending temperature. a fixed orifice or piston meters a set amount of refrigerant controlled by piston size. </p><p></p><p>dialing correct amount of refrigerant for TXV is different vs piston. with TXV using subcooling one needs to insure a full stream of liquid refrigerant just before TXV but not so full system slugs liquid to compressor which can kill it ... to properly charge a piston unit one needs to measure superheat ... measure wet bulb temperature at intake duct. then measure outside temp by condenser. the correct superheat range can be found using a chart for fixed metering devices. </p><p></p><p>then factor HVAC work is one of the most equipment intensive or all the trades ... a competent/honest tech is an asset! you cannot blame a pro for not wanting to explain how to fix your HVAC unit .. it might have taken him years to figure out .. not to mention the very expensive/on going costs for equipment. then factor all the new equipment coming out ... for instance above explanation for variable fan speeds can be thrown out for ductless mini-splits .. which can use DC driven variable speed compressors and fans. </p><p></p><p>here's my latest equipment purchases .. Appion G5 recovery unit and Digicool AK9000</p><p><a href="http://postimg.org/image/hsr55rsln/" target="_blank"><img src="https://www.okshooters.com/data/MetaMirrorCache/s25.postimg.org_hsr55rsln_DSC05676.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p><p></p><p><a href="http://postimg.org/image/ldn0ozx57/" target="_blank"><img src="https://www.okshooters.com/data/MetaMirrorCache/s25.postimg.org_ldn0ozx57_DSC05679.jpg" alt="" class="fr-fic fr-dii fr-draggable " style="" /></a></p></blockquote><p></p>
[QUOTE="_CY_, post: 2776580, member: 7629"] when sizing a non-spec build it's better to round up a 1/2 ton vs down. reason is simple .. a bit of headroom for extreme temps can be a good thing. you just don't want to be way off .. like say installing a 5 ton on a 1500sf home. but if you are that close rounding up or down, both will probably work fine. to explain why one constantly sees .. "call a pro" .. HVAC work can get very complex in a hurry. correctly diagnosing what's actually wrong can make a HUGE difference in costs to fix. below goes into a tiny portion of what a competent HVAC tech does ... for instance your example above of variable fan speed and sizing really has little to no relevance. variable speed fans are controlled by newer units with electronic boards. low speed to keep air constantly moving .. medium speed for heater which needs slower air speeds .. high speed if needed to achieve air flow needed to meet AC mfg spec's or what ever ... your AC is spec'd by the factory for XX CFM airflow to keep coils from freezing up. then we get into metering devices .. TXV or piston .. superheat is the amount of heat removed by refrigerant after it passes through A coil or evaporator. a thermal expansion valve will open or close depending temperature. a fixed orifice or piston meters a set amount of refrigerant controlled by piston size. dialing correct amount of refrigerant for TXV is different vs piston. with TXV using subcooling one needs to insure a full stream of liquid refrigerant just before TXV but not so full system slugs liquid to compressor which can kill it ... to properly charge a piston unit one needs to measure superheat ... measure wet bulb temperature at intake duct. then measure outside temp by condenser. the correct superheat range can be found using a chart for fixed metering devices. then factor HVAC work is one of the most equipment intensive or all the trades ... a competent/honest tech is an asset! you cannot blame a pro for not wanting to explain how to fix your HVAC unit .. it might have taken him years to figure out .. not to mention the very expensive/on going costs for equipment. then factor all the new equipment coming out ... for instance above explanation for variable fan speeds can be thrown out for ductless mini-splits .. which can use DC driven variable speed compressors and fans. here's my latest equipment purchases .. Appion G5 recovery unit and Digicool AK9000 [url=http://postimg.org/image/hsr55rsln/][img]https://www.okshooters.com/data/MetaMirrorCache/s25.postimg.org_hsr55rsln_DSC05676.jpg[/img][/url] [url=http://postimg.org/image/ldn0ozx57/][img]https://www.okshooters.com/data/MetaMirrorCache/s25.postimg.org_ldn0ozx57_DSC05679.jpg[/img][/url] [/QUOTE]
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