When you look at Manual J reports, you’ll see the loads. They’re shown separately for heating and cooling, and cooling is further divided into sensible and latent. When the contractor or designer picks a piece of equipment, they’ll have to go through a “derating” process to match the equipment’s performance specifications with the building’s loads. (For more on this, see “Manual J Doesn’t Tell You Equipment Capacity.”)I mention this topic here because some Manual J reports can confuse you on this distinction, especially for cooling. Depending on which reports you’re looking at, you may also see something like “Req. total capacity at 0.70 SHR.” That’s just a guess at what equipment capacity you’ll need. If the person who ran the calculations has already gone through the derating procedure and specified the equipment, it may be accurate. Or the designer may have left the default number in there for SHR (sensible heat ratio), in which case you should look at that number simply as a suggestion.In the end, just remember that the load calculation comes first, and your equipment capacity is going to be a bit bigger than the loads.Notes on terminologyIf you’re going to read Manual J reports, knowing a little about the terms used will help you understand them. Here are a few that you need to know:One ton of AC capacity is equal to 12,000 BTU/hr.BTUh is the same as BTU/hr.Sensible cooling results in lower temperature (technically, dry bulb temperature); latent cooling results in lower humidity through condensation of water vapor on the coil.SHR is the sensible heat ratio. It’s obtained by dividing the sensible cooling load by the total cooling load. For homes in eastern North America, the humid side, that number often comes in at 0.8 to 0.9, sometimes even a bit higher. In dry climates, it can be 1.0 when ventilating with outdoor air.A rule of thumb you can useI often rail against rules of thumb when it comes to HVAC design (or lack thereof), but that doesn’t mean you can’t use one to your advantage. This is the sniff test you can do to see how close the designer might have come to an accurate load calculation. In the warmer climates where air conditioning is a big deal, the rule of thumb used by many contractors for sizing an air conditioner is usually this:AC capacity = CFA ÷ (500 sf/ton)CFA is conditioned floor area in square feet.Sometimes the rule is 400 sf/ton, sometimes 600 sf/ton. But it’s always right in that neighborhood. So if you get a load calculation report, find the total cooling load (sensible plus latent) and divide it by the conditioned floor area. If it comes out around 500 or 600 sf/ton, the designer fudged the calculations somehow to align them with their preconceived idea of how big the loads should be based on their rule of thumb. (I’m talking about new homes here, or complete gut-rehabs. Existing homes generally have higher loads.)Don’t believe me? Take a look at our data. The graph shown in Image #2, below, is from an article I wrote in 2016 about the results of our load calculations on 40 projects. (Go read the article for full details.) The takeaways here are that our worst result was 624 sf/ton. The average 1,431 sf/ton.If you’re building a well-insulated house with a good level of airtightness, double-pane low-e windows, and decent specifications overall — in other words, a house that meets most state energy codes these days — your result should be 1,000 sf/ton or higher. If it comes in lower that, you should see that as a red flag and delve into the details to see if the designer made mistakes.Delving into the detailsFinding the loads. First, identify the results for heating and cooling loads. The two main software tools for doing load calculations are Wrightsoft’s RightSuite Universal and Elite’s RHVAC. The reports look a little different but it’s not too hard to find the results. Both types of software make it clear how many BTU/hr you need for heating and for cooling. And for cooling, they also break it down into sensible, latent, and total. From the total cooling load, you can calculate the sf/ton I mentioned above. RightSuite doesn’t do it for you, but Elite’s software does. In the Project Report, they include a section called Check Figures that includes the sf/ton.Checking the details. If you suspect that the loads may be too high — or too low or about right — you can check the details to see if the designer got the inputs right. Here are some of the main things to check:Indoor design temperatures. The standard indoor temperatures are 70° F for heating and 75° F for cooling (with 50% relative humidity).Outdoor design temperatures. The outdoor design temperatures depend on where you are, and you should check to see what was entered versus what should have been entered. It’s pretty easy to find the entries on the reports. To find what should have been entered, you can go to this page on the International Code Council’s website. If the entries in your calculation are off by a couple of degrees, it’s not a big deal. If they’re off by 5 degrees, you should ask for it to be corrected.Areas. When the designer enters the various floors, walls, ceilings, windows, and doors, having the wrong areas can make a big difference. This is especially true for parts of the building enclosure that have worse specifications, like windows. A code-built house in IECC climate zone 3, for example, has windows that are about R-3 whereas the walls will be R-13. Entering too much window area is a way to inflate the load. Entering too much of any of the areas likewise inflates the load.R-values and U-factors. Check the entries for the floors, walls, ceilings, and floors to ensure the designer put in the correct R-values (for insulation) and U-factors (for assemblies like windows).Number of occupants. A common way to inflate the cooling load is to add extra occupants. The rule here is that the number of occupants should equal the number of bedrooms plus one. If they put 23 people in a 5-bedroom house (yes, I really saw that!), they’re adding unnecessary load. At 230 BTU/hr sensible and 200 BTU/hr latent, those 17 extra occupants added more than a half ton of cooling load.Infiltration. Did they use a simplified input method? If you’re building a new house and meeting a code that requires 7 air changes per hour at 50 Pascals (ach50) or better, the entry should be tight or maybe semi-tight. Better would be to use an actual blower door number. For example, if your code requires 3 ach50, enter that into the calculation. If you’re going for Passive House certification, enter 0.6 ach50 or 0.05 cfm50/sf of enclosure.Orientation. The software gives the designer the option of using worst case for the orientation. Your load calculation should have the correct orientation or you’ll end up with extra load in your reports.Duct location. If the ducts are in conditioned space or in an encapsulated attic or crawl space, make sure that gets factored in properly. Doing the load calculations for ducts in an unconditioned attic will result in excess load.Contractors doing these load calculations often feel compelled to stretch a little bit here and a little bit there. Each litte bit doesn’t affect the overall load that much, but by the time you add them all up, you’re looking at putting in a 4-ton air conditioner where 2.5 tons would work. But here’s the thing: Even when you’re as stingy as possible with things that add load, you still end up oversized. So there’s no need to add extra load. If you’re building or remodeling a high-performance house, make sure the load calculation is correct. It’s worth it. Allison Bailes of Decatur, Georgia, is a speaker, writer, building science consultant, and the author of the Energy Vanguard Blog. You can follow him on Twitter at @EnergyVanguard. RELATED ARTICLESSaving Energy With Manual J and Manual DWho Can Perform My Load Calculations?Manual J Load Calculations vs. Rules of ThumbHow to Perform a Heat-Loss Calculation — Part 1How to Perform a Heat-Loss Calculation — Part 2Calculating Cooling LoadsWhen Do I Need to Perform a Load Calculation?We Are the 99% — AND the 1%Air Conditioner Basics When you enter the world of building science — whether through building a house, becoming a home energy rater/building analyst, or just hanging out in cyberplaces like this — everyone talks about the importance of getting actual heating and cooling load calculations based on ACCA Manual J. A great number of HVAC contractors sell and install oversized equipment with air distribution systems that don’t work because these contractors base their choices on rules of thumb.OK, but what if you hire a contractor or third-party designer to do Manual J load calculations and you’re not an expert and don’t want to be? Suddenly you’re faced with a bunch of seemingly indecipherable reports. How do you know if they’re accurate or not?Fear not, dear reader. I’ve got some help for you today.Don’t confuse load with capacityI don’t think I can make this distinction often enough. Heating and cooling loads are not the same as the equipment capacity needed. I just did it in my last article, and now I’m doing it again. It’s that important. The first thing you need to know is that the term loads refers to how much heating and cooling the building needs and capacity refers to how much heating and cooling the equipment can supply. Here in the U.S., both are measured in British Thermal Units (BTU) per hour.
STOMACH SICKNESS?Kanter posted a video of his “cheat day” meal on Wednesday, with seven burgers and a plate of fries on the table in front of him. He then missed practice Thursday and the game Friday because of illness, leading to speculation that he had ate himself sick. But Fizdale thought there was no way Kanter actually ate all that food.“The guy walks around with his shirt off all day in the locker room. There’s no way he’s stuffing seven burgers down his face. I just don’t see that,” Fizdale said. “I think sometimes people take the ‘gram too seriously.”UP NEXTPacers: Host Phoenix on Tuesday.Knicks: Host Philadelphia on Sunday.Sports Related Videospowered by AdSparcRead Next “It felt good to play here,” rookie Kevin Knox said. “Not the result we wanted, but it felt good to finally be back at Madison Square Garden.”New York battled back from 13 down to take the lead on Tim Hardaway Jr.’s second straight 3-pointer, but with the game tied, Indiana scored the final 12 points, with Oladipo hitting consecutive 3-pointers, to make it 64-52 at halftime.Bogdanovic then opened and closed a 16-7 spurt out of the locker room with 3-pointers to open an 80-59 cushion.Hardaway played just a minute of the fourth quarter before leaving for good because he was cramping. He said he expected to be fine.TIP-INSPacers: Turner has a sore right shoulder. … The Pacers have won the last five meetings.Knicks: New York played without Enes Kanter (illness), Frank Ntilikina (sprained left ankle) and Mitchell Robinson (sprained left ankle). … Knox was presented with the Eastern Conference rookie of the month award for December before the game. … The Knicks celebrated Croatian heritage night. Hezonja and Bogdanovic are Croatian, with Bogdanovic the leading scorer in the 2016 Olympics with 25.3 points per game.PORZINGIS PROGRESSKnicks coach David Fizdale said the team is leaning toward leaving Kristaps Porzingis home next week when the Knicks travel to London to play Washington, believing that is better for the All-Star forward’s rehabilitation from his torn ACL than traveling. Fizdale said he spoke Friday with Porzingis, who is scheduled to be re-evaluated in about a month. He said Porzingis’ spirits were positive.“Obviously he misses playing, that part has been hard,” Fizdale said, “but he’s starting to get stronger, so he’s feeling better. And he seems to be in a really good place.” Sabonis shot 9 for 14 from the field to finish 21 of 26 this season in two games in New York. Playing as a reserve, he made all 12 shots and tied his career high with 30 points when the Pacers won here on Halloween.Starting this time with Myles Turner out of the lineup, he led six players in double figures as Indiana shot 52 percent. He couldn’t explain why he is so good in New York.“I treat every game the same way,” he said. “Come out, my teammates do a great job of finding me and I just try to do my job.”Bogdanovic had 15 points.Emmanuel Mudiay scored 21 points for the Knicks, back from a lengthy, six-game road trip and playing their first game at Madison Square Garden since Christmas. They lost their seventh straight at home.ADVERTISEMENT SEA Games hosting troubles anger Duterte Is Luis Manzano planning to propose to Jessy Mendiola? Indiana Pacers forward Domantas Sabonis reaches for a loose ball during the second half of the team’s NBA basketball game against the New York Knicks, Friday, Jan. 11, 2019, at Madison Square Garden in New York. The Pacers won 121-106. (AP Photo/Mary Altaffer)NEW YORK — Beaten badly in Boston, the Indiana Pacers shifted their energy to finishing their road trip with a winning record.It helped that it ended in a building where Domantas Sabonis barely misses.ADVERTISEMENT SEA Games: Biñan football stadium stands out in preparedness, completion Don’t miss out on the latest news and information. LATEST STORIES TS Kammuri to enter PAR possibly a day after SEA Games opening PH underwater hockey team aims to make waves in SEA Games PLAY LIST 02:42PH underwater hockey team aims to make waves in SEA Games01:44Philippines marks anniversary of massacre with calls for justice01:19Fire erupts in Barangay Tatalon in Quezon City01:07Trump talks impeachment while meeting NCAA athletes02:49World-class track facilities installed at NCC for SEA Games02:11Trump awards medals to Jon Voight, Alison Krauss Hawks pounce on Jimmy Butler’s miscues, stun 76ers on John Collins’ late jumper Private companies step in to help SEA Games hosting Hotel management clarifies SEAG footballers’ kikiam breakfast issue SEA Games: Biñan football stadium stands out in preparedness, completion LOOK: Joyce Pring goes public with engagement to Juancho Triviño MOST READ Sabonis had 22 points and 15 rebounds to cap his sizzling season at Madison Square Garden, and Indiana bounced back from its worst performance of 2018-19 by beating the New York Knicks 121-106 on Friday night.Victor Oladipo added 19 points for the Pacers, who finished 3-2 on their longest trip of the season. They yielded season highs of 135 points and 56.8 percent shooting in their 27-point loss in Boston, and spent two days talking about finishing strong.FEATURED STORIESSPORTSPrivate companies step in to help SEA Games hostingSPORTSUrgent reply from Philippine football chiefSPORTSWin or don’t eat: the Philippines’ poverty-driven, world-beating pool stars“Even though we were 2-2 we felt like we hadn’t played our best basketball,” Oladipo said, “and I think we came out today with a chip on our shoulder and we did a great job of using that intensity and that edge and going out there and playing with that chip.”And with energy and anger. Oladipo threw down a dunk over Mario Hezonja, and Sabonis and Bojan Bogdanovic both had powerful slams in the first half. View comments