Advanced HVAC Training for Raters

Ok, I admit it, this post is about a week late as I took this class last Friday after completing the two Day ENERGY STAR® V.3 Training. This is what I would refer to as a one off class – that is it is only offered by Energy Vanguard, covers the basics listed below, and is semi tailored to the needs or wants of those taking it. One of the most interesting items in our class was we actually had an HVAC installer & Rater, in there, to learn more about his field, how it affects the overall picture, and how he can improve.

Identify HVAC systems & components

Piece of cake right, I mean anyone that has been in the trades for any length of time knows what all the components are, right? We should just be able to take one look at it & know exactly what type of unit it is, without hesitation. Gas furnaces are easy… or are they; is it a condensing type with an efficiency of 92-95%, a regular one with an efficiency of 60-68% or is it 78-80%?

• Condensing furnace extracts heat from water vapor (One by-product of combustion), where water goes to a condensate pump & utilizes PVC for exhaust
• 60 – 68% has a metal exhaust & uses an always on pilot light
• 78/80% – also uses metal exhaust, but the pilot light is an automatic start

There are two general layouts for combination systems, which is dependent on the fuel source.

• Gas heat: Return plenum – Blower – Heater/furnace – cooling/evaporator coil – Supply plenum
• Electric & other types of heat sources: Return plenum – cooling/evaporator/hot-water coil (hot water coils – rare in south) – heat strip (if not handled below) – Blower – Supply Plenum

Understand the refrigeration cycle

There are four parts to the refrigeration cycle, which he is famous for making students re-enact in the class after he explains them. While I am not going to give away his teaching system (ok, I thought it was a little lame, but if it helps and works for others – that’s great), I will briefly cover the cycle here.

• Compression: Starting with the compressor the incoming vapor is compressed down to 2-3 times from its original volume. It leaves the compressor at around 190-200° as a High Pressure (280 PSIA) vapor
• Condensing: The vapor soon enters the condenser coils, where the heat is lost to surrounding air or other medium (now done to 110-120°) and changes from a vapor to a High Pressure liquid.
• Expansion: This liquid now hits the expansion valve where it changes over to a Low Pressure state (85 PSIA) and the temperature drops dramatically to the 40-50° mark
• Evaporation: As this liquid flows through the evaporator coil, the moving air or other medium gets to pull the “coolness” from it & replace it with the heat it is trying to shed. This changes the liquid back to a gas state (about 10° warmer) where it can start the process all over again.

Deal with HVAC design issues – Manual J, S, T, & D

Bring in the Architect… At this point Allison turned the class over to Chris, who went over what the actual manual’s looked like (J, S, T & D – or as I like to call it J-STanDard or J-STD for short) and what they each cover.

• Manual J: Based off SF, Insulation, window values, room layout, it determines what the heating & cooling loads will be & airflow required by room
• Manual S: Selection of equipment – while there is not a printout available for this, it is where the designer flips back and forth through numerous charts & selects the correct equipment that will best meet the loads & airflow required by the Manual J
• Manual T: Selection of distribution – flex pipe, metal ducts, square, round, etc… (also no printout available)
• Manual D: Once the distribution, unit, and loads are all calculated – this is where the duct design, return types, and equipment placement is figured out. A printout is made of this and handed off to the installers to make sure everything is installed properly to meet the needs of each room

Chris then took us into one of the two main programs generally used, which was by Wrightsoft software (the other one is by Elite (I swore they said Insight, but I might not have heard it properly / can’t find it?)). While going through the demonstration, a few items stood out on why there is such a disparity between different programs and the unit size listed. In the case of RemRate, it bases its calcs not off each rooms needs but the whole house, whereas as properly done Manual J looks at each room individually.

On the flip side, Wrightsoft does have a few bugs which your designer has to watch out for. One of the biggest ones is how it calculates the U-Factor of a section, because when more insulation is added to a wall, the U Value should drop, not increase. While one can get away from using their prebuilt sections & adding insulation to them and going into a custom layer, it should not take much to fix that issue. Even so, it pays to pay attention and double check the numbers as shown by that & even what RemRate comes up with as shown in the previous class. (One nice note, is that you can import a file into RemRate from either of these programs or vice-versa which should help cut down on the duplicate data entry)

The final three:

• Learn the details of ENERGY STAR’s right-sizing rule for cooling systems
• Understand air flow and static pressure
• Commission a new HVAC system (the basics)

Ahhh, I guess you will need to take the class to learn the rest… but in closing, I will leave you with one video of Allison explaining the Bernoulli principle.

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