In this video, we'll be looking at what's needed to calculate the heat loss and heat gain of a residential building. We'll be talking about the application of conduction convection radiation, but we won't be covering the basics of heat transfer in much detail. If you want to brush up on the basics of heat transfer before watching this video, click on the link above or in the description to view our previous videos. All about the basics of heat transfer in a building.

An HVAC Trade for residential buildings. We use AKA Manual J to calculate heat losses and gains in residential structures. Manual J is one of the design manuals from the Air Conditioning Contractors of America also known as Akka. Proper System design requires math and nowadays we use software to help us out with the calculations, but Manual J will let you know which measurements you need to make an accurate load calculation.

This video will hopefully help you understand why those measurements are important for calculating indoor heat loads. Before we can calculate the heat gains and losses in a residential building, we need to know a bit about the structure. Specifically, we need to know the area of all the different surfaces in the building before we can calculate heat loads. Now, you're going to notice in this video we are talking about block loads on an existing home.

There's also something called room by Room Manual J Load calculations where you calculate each room independently and in many cases Manual J Calculations are done based on a set of plans for new construction. In this case, we're talking through a block load for an existing home. It's important to be detailed when considering walls. Understanding the R value of insulation is important, but the building materials in the wall also have R values that need to be accounted for.

We can control the wall thickness and insulation to minimize conduction. Manual J requires us to know the walls r value, which gives us an idea of how much the wall will resist conduction. Different materials or similar materials of varying thicknesses will have different R values. A higher r value indicates that material resists conduction well, and a lower r value indicates the material isn't as effective at resisting conduction.

The insulation in this case is located between the studs. So when calculating the r value for Manual J You'll need to consider the wall insulation and studs, you'll need to deduct the studs as well as any windows and doors. When measuring the R-value of a wall, Manual J has assumed percentages for study area depending on the actual stud spacing. This might sound intimidating, but an ACA approved software will calculate this for you.

As you can see, a wall without insulation will have a lower resistance or R value than a wall with insulation. The rate of heat transfer via conduction is significantly higher in walls that lack insulation. It's important to note if the exterior walls are adjacent to another space such as a neighbor or an unconditioned garage. these partition walls will have a different delta T or temperature difference than an actual exterior wall.

As said earlier, you'll need to deduct windows and doors from the total area of a wall, Take the area of the wall, and then subtract the area of the window to calculate the heat losses and gains of the wall. The window will have its own calculated heat loss or gain. Windows are also responsible for allowing heat gains via solar radiation. These gains will vary depending on the placement of Windows and the time of day.

For example, more heat will pass through a window facing west during the last few hours before Sundown because the sun sets in. The West manual J requires us to know the size of Windows, what material they're made of, what side of the house they're on, transparency, the type of window, the framing, and the number of panes. To understand the U factor, a high U Factor indicates a higher rate of heat transfer through a given substance. We can think a view Factor as the inverse of the R value.

Overhangs on roofs can reduce the amount of solar radiation that enters a window by blocking those electromagnetic waves from passing through the glass. The overhang height and depth needs to be accounted for whenever we do a load calculation. In addition to the overhang, we should know the roof type, pitch, and color for our load calculations. All of these things will affect heat gains through the roof or Windows As you can see, a manual J calculation requires us to collect quite a few pieces of field data and take several measurements.

When we're looking at exterior doors such as a front or back door, we need to think about the door size, material, and what side of the home it's on. We also need to know the elevation of the home and how many stories it is. In addition to knowing how many stories it has, we need to figure out the ceiling height for each level. As with the walls, we need to know the r value of the ceiling and understand something about its construction, especially as it separates the home from an attic or an upstairs neighbor.

A common ceiling insulation r value would be R39 as shown here, conduction can also happen through the floors, and Floors come in a few different variations and can even have insulation like ceilings. Floors can separate the conditioned space from garages, basements, and even Neighbors Ductwork also has to be considered and may be contained in crawl spaces in an attic or a basement. The ductwork may have insulation, which we also need to think about in a manual J load calculation. This insulation slows down conduction into or out of the ductwork just like the insulation in walls or floors.

As with wall and floor insulation, duct insulation also has an R value, which will typically be R4, R6 or R8. Most modern codes call for R8. duct installation. Regardless of what the R value really is, we'll need to factor it in for our load calculations.

As with gaps and cracks and walls, poorly sealed ductwork can allow air to pass in or out of the ductwork via convection. Leaks in the ductwork will cause you to gain or lose BTUs And you can measure duct leakage with a duct tightness test. Leaky ductwork can change the load calculation by a substantial amount, so it's a good idea to account for those BTUs during your load calculation. Or better yet, if the ducts are very leaky, upgrade the ductwork as part of a retrofit or make it an option.

We also need to know if the air handler or furnace is in a conditioned space or an unconditioned space. In many cases, such as this one, the air handler is in a garage or an attic. These are usually unconditioned spaces, but Air Handlers may also be in closets within condition spaces. In this example, 100 CFM of exhaust only ventilation would be responsible for 1764 BTUs of heat loss in the winter.

In the summer, we can expect infiltration to be responsible for 1198 sensible and 2004 latent BTUs of heat gain in the summer. Thank you Appliances also add Heat The default Appliance load from manual J is 1200 BTUs Electronics such as TVs and computers also give off heat when they run. The data shown here is from a real life calculation. Notice that the dishwasher adds latent BTUs or the other appliances do not, and homes for occupants will wash a lot of dishes or clothes or take many showers.

We can expect significant latent BTU gains. Occupants also add to the sensible and latent heat loads. Typically, a single person gives off 200 latent BTUs per hour. On the sensible side, we can expect a single person to add 230 sensible BTUs per hour When you're calculating BTU loads based on the number of occupants, Manual J looks for the number of bedrooms plus one.

For example, if you have a three bedroom home, you would calculate the heat load for four occupants. Keep in mind that appliances will not run all the time. There'll also be times when there are more or fewer occupants than the load calculation accounts for. When we use manual.

J We'll need to weigh the probability of appliances running during the hottest hours of the hottest days and base our calculations on that table. 6A can help you determine additional sensible and latent loads based on occupant lifestyle. Using all the data we've gathered, we can finally put it all together and finalize our load calculation. There are many types of software nowadays that can help you determine your heating and cooling loads.

You can use any software you're comfortable with as long as it's approved. We've chosen to use Quick model with energy gauge loads for this video. Foreign: this is how you collect data from manual J load calculation as well as a little bit about it. Once you know your total Heating and Cooling loads, you can use those numbers to select your equipment.

We'll be doing a 3D demonstration of equipment selection with manual S, so be sure to keep an eye out for that video as well. Thanks for watching! If you're willing, give this video a thumbs up and drop us a comment Don't forget to hit that Bell icon to stay updated with all of our future videos. And as a quick reminder: HVAC School isn't just a YouTube channel. Dive deeper with us at our main website Hvacrschool.com Curious for more knowledge on the go? We've got you covered! Tune in to the HVAC School podcast available on all your favorite podcast apps.

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