Must be a big secret!
With all the talk about confusion on which equipment to buy being it 12 SEER or 20 SEER. This brand or that brand. 80+% or 90+%. With all this talk why we do not talk more about proper sizing. The increased fuel savings and improved comfort levels of properly sized equipment is so dramatic and everyday many many many units are installed at 100 to 200% over sized. This wastes fuel and increases maintenance. As professionals we need to emphasize the importance of proper sizing of equipment. I have been asking around the heating and air conditioning companies if they do a heat loss. I am surprised that less that 15% actually does a heat loss/gain when replacing equipment.
The second thing is with boilers about half will actually properly adjust the heating curve on outdoor reset controls.
Our industry has been talking about heat loss/gains for many years. It is easier to just size from rules of thumb. We would have been much further ahead giving tax breaks on actual heat loss calculations than efficiencies.
Again, as professionals we must do what we can to properly size equipment which means lower equipment costs, improved comfort, less maintenance, increased efficiency and less noise.
I think the first word out of everyones mouth around here is, who did a load calc?
On the other hand I've got quite a few customers that would value pull down times above energy efficiency no matter how much I go over the benefits. So do I lose a customer because they dont want it sized right?
We do abbreviated loss calcs. to make sure we are sized properly. I have a couple dozen custom templates loaded on my lap top along with Wright J so plugging in numbers only takes 10-15 minutes. My customers almost always take my advise as far as size, type and brand of equipment and I can't think of one instance where I lost a job due to calculating the proper size of equipment, I have however, picked up more jobs than I can remember because I did it. Our country building department has adopted Rescheck and has stopped requiring Manual J and Manual D schedules be submitted for issuance of new construction building permits. I seriously doubt they actually looked at them anyway but they still need to be done, how else are you gonna know what your needs are.
A good HVAC tech knows how, an educated HVAC tech knows why!
How useful and accurate is the HVAC Calc software offered on this website?
It seems none of the contractors who have submitted bids did any sort of formal heat calc, so I decided I needed to do one myself. I can hear your responses now. If they don't do a manual J, manual S, and manual D then show them the door. If I follow that advice, there will be no one left to deal with! Sad but true.
Can I rely on the numbers this software generated?
If I going to spend big bucks on a complete system, I can't afford to screw it up because I have inaccurate heat calc numbers due to this software. And I wasn't inspired when the seller of the software said he was "only a programmer, not a contractor".
Not trying to step on toes, just need feedback from anyone who has used the software be it successfully or unsuccessfully.
CB, I'm in NW Arkansas and made a Manual J a requirement for all proposals. Most did it. However, after advice from this forum, I allowed some to use the Manual J, blower door and infrared camera study I got from our electric Co-Op, Ozarks Electric. This cost me $100 but I wanted to have an analysis of our house which we did not build.
Originally Posted by chambery1
By the way, since the existing split AC/furnace was performing good enough, I also required that no proposer bid an AC component that exceeded the current capacity.
It can be done. Just write your requirements down and tell every contractor he must respond to them.
He followed manual J for the programming it is accurate. Any heat loss will actually oversize equipment slightly, maybe 15 - 20%. I usually suggest homeowners get the heat loss done so all the contractors bid on the same size unit thus apples to apples. When I was a contractor we did heat loss but never put the size on the proposal. We would include the manufacturer and general model number but not the part that dictated the size. They got an updated proposal when and if they decided to sign. We did not want to do unpaid consulting.
There are places the home owner can get on on-line heat loss done which includes everything they would need to do if they ran it themselves, but the info is entered by professionals to verify it is entered properly. They also can ask questions when things don't make sense.
Of the 4 different contractors I met with before my install, all used rules of thumb, no man J. Not being in the business, I had no idea there was such a thing as manual J until after my stuff was already installed.
The programmer specifically states in his documentation, twice, that the program does not oversize in ANY way, he repeats, "There is no safety factor built into the program. The results are as accurate as possible. Just in case you missed that, there is no safety factor built into the program."
Originally Posted by rbeck
Then he goes on to talk about sensible output ratings on A/Cs and HPs. He says if the mfgr. data is not available, a good rule of thumb is to use 72% of rated BTUHs as the maximum sensible output.
Using the mfgr's actual data on a 3.5 ton system shows sensible output of 33,400, while the HVAC-CALC program returns a sensible requirement of 36,000. So this 3.5 ton unit would be undersized for design temp and I need to go to a 4 ton unit, or the program and/or it's theory is flawed.
Comments on man. J calcs for sensible heat versus sensible output for a particle unit?
Comments on the programmer's advice re: sizing for sensible heat?
As long as we are talking about neglect, how about including some fresh air ventilation into our new system in the new energy efficient homes. An interesting process when doing load calcs, plug in .2 ACH of fresh air during low/no cooling load conditions. 2-4 occupants with 100 cfm of 70^F dew point outside air is 4-6 lb./hour moisture load. We all see this condition for days on end. Our defense is to avoid all fresh air possible. This produces an indoor air quality problem that is chemical soup. Some do not care while others will purchase a solution.
In green grass climates, a ventilating whole house dehumidifier is a solution to the opportunity. Many manufactures are suppling these units. As an a/c trade group, we do a poor job of creating awareness. The a/c mfgs. will not admit to the limitation of being unable to maintain <50%RH during low/no cooling loads. So the a/c trades only solution is to elimainate all fresh air possible.
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"
In simple terms, the program tells you what (sensible) you need; the mfg's specs tell you what the equipment delivers. You need to select equipment that will deliver the required BTUs.
Originally Posted by chambery1
You want some more head spinning? Search (here) for 'derating air conditioners' and ARI (or AHRI) conditions'.
I'm curious; how many contractors have done a Manual J and had the recommendations match the currently installed heatpump/AC and furnace?
I do believe that doing some kind of load calculation (preferably the Manual J) is the right thing to do. I think if the local utility companies took the lead this would help lead less energy usage. If the contractor installs the wrong size system it obviously might use more energy.
My mom, in Kansas City, had a new heatpump and furnace installed. She explained that the contractor did a Manual J, going from room to room measuring etc. The local utility company, KCPL, requires contractors to do this in order for the customer to get a rebate.
Contrast this to Maryland, where I live. The rates are about twice as much, having gone up around 80% or so in the past couple of years. They are just now coming aboard with offering rebates for customers installing energy efficient heating and cooling equipement, but they don't require the the contractors to do any kind of heat loss calculation to size the equipment, go figure.
The local utility company, BGE, does have a lot of great programs, but they seem to have missed the boat on load calculations. They suggest that load calculations be done. They suggest don't just replace new equipement with the same size as old. They do a visual audit to ensure that the equipment you said was installed is installed, but there is never any proof required that a heat load calculation was done. This is interesting since they go through all the trouble to make sure that the contractors are licensed and insured. Maybe it's the close proximity to DC that causes them to forget to do all the right things.
I find that most of the equipment is in the range of 100% over sized. This is not a rule to just cut the appliance size in half. I am amazed that a heat pump will be sized let's say for 3 ton. This is 36,000 btu's with some back-up electric. When the electric kicks on the heat pump is not putting out near 36,000, assuming it is a 12 SEER or less. The electric back-up is 10 kw. The a furnace is installed and rated at 80 or 100k. If the heat pump is doing the job at 36K why such a big furnace?
When I worked for the oil company we did heat losses. We say the average fuel reduction of 25 - 40% savings and the appliance was a minimum of 50% smaller but usually 100% or more. We had one which really sticks in my mind that we tore out a 320k boiler and installed a 125k. Fuel bill went down 73%.
Here are some sites to look at.
Interesting info and sizing info
My experience shows that boilers are some of the biggest offenders when it comes to being grossly over sized. Most were installed by plumbers who really don't have a background in HVAC as such. Things are changing slowly, separate licenses for hydronics is one way, education is another.
A good HVAC tech knows how, an educated HVAC tech knows why!