View Full Version : Hvac-calc
03-19-2008, 10:20 PM
The HVAC-CALC manual suggest adding in 20% to the calculated load.
Do you also add 20% to the CFM?
I have a Infinity Heat pump that was installed by the contractor we selected. At the time we were negotiating they wanted us to go with the zoning package but we declined because of cost. Is there any other place to get the Infinity zoning other than a Carrier dealer?
The system we had installed is the Infinity 17 38YDB0060/FE4ANB006.
Would someone like to take a look at our number s and see why I have such a big system? Works great though.
03-19-2008, 10:34 PM
Cieling load, basement or floor load?
Put the whole calc here.
03-19-2008, 10:48 PM
Im Sorry, not sure what you are asking? I posted the report. Do you need one with more info?
03-19-2008, 10:59 PM
if you add 20% to the load then you need to match the load to the equipment that will handle the load. It gives you a cfm selection but you have to chose the equipment in order to know what cfms you will be using
03-19-2008, 11:04 PM
Has that 5-ton Infinity ever gone into 2nd stage--for a reasonable amount of time? You should be able to check this on the Infinity control.
03-19-2008, 11:31 PM
Thats a good question. How would I tell? I am sure it's om the thermostat and I know how to enter the service menu.
03-19-2008, 11:38 PM
Someone fluent with the Infinity control will have to direct you there. I looked online but I'm not sure if I should give this sort of information on a public forum per site rules, since it would allow other information/settings to be visible and maybe even editable.
03-20-2008, 07:58 AM
I don't see a people load on that report.
Nor did I see an infiltration load.
These would be needed to see if you made a mistake.
And then over the internet its stillnot something we can tell for sure.
That program also wants you to list 2 people per bedroom, did you.
What infiltration rate did you use.
Also, make sure you have orientation correct, that also makes a big difference.
HVAC CALC tells you the capacity the unit must deliver, NOT the nominal rating.
In your report, you need a unit that can remove 28,150 BTU's sensible, at a 75*F indoor temp, many 3 ton units can't do that.
Carrier Infinity zoning system=Carrier dealer.
03-20-2008, 06:28 PM
OK, Lets try this report. I did make some changes based on people and now it says I need a 3.5 ton. This is without any fudge factored in. Infiltration is listed on the report and I selected normal construction which this house is not. We have an excellent vapor barrier with Ty-vex that I personally sealed every joint with the tape.
03-20-2008, 09:55 PM
Where is your ductwork located. That can add load also.
A 3.5 ton heat pump won't meet your sensible load at your ID design temp, so they allowed for that and increased its size base on that.
If your ductwork is in the attic, they may have allowed for the additional load it adds.
Yaking into consideration the load on the ductwork, and the derate for the ID design temp it may have to be a 4 ton unit ot meet your requirements.
After that, they may have gone the next size up because its a heat pump, trying to save you money on your heating bill.
They may have used lower insulation valvues. Different load programs use different values for infiltration, and that will change the load it says your house needs.
Of course thats speculation that they did a load calc.
03-21-2008, 07:13 AM
I counted 33 people added to these rooms. I would only add people to the areas where they will be during the hottest time of the day Peak load. Get rid of all those people and keep people in the main rooms of the house. Do you see your self haveing 33 people in the house between 2 and 5 pm ? I allso add 20 percent to my heat load only. other may differ but I can say what works for me.
03-21-2008, 07:35 AM
I didn't take notice to that.
Gotta wear my glasses more often.
03-21-2008, 11:43 PM
Duct work in basement. I added people based on one of the post.
As stated do I need to increse CFM for each room by the amount of increase in unit size
03-22-2008, 09:23 AM
once your sure of the calculations inputs and results. you can go to the tools at the top of the program and select cfm calculation. you must know the amount of CFM /tons cooling size. an axample type in 1200 cfm for 3 tons and it will tell you according to the calculations where the cfms should be per rooms. add the ductwork one time to the program input .Adding the people the way i explained it was how it was explained to me by the company who sells the program.I have been faithfully useing this program on every single job for 3 years now.I will admit that I have not derated any of my jobs. and have had very satisfyed customers. This was something I overlooked until recently reading the threads on the issue. maybe in jersey it was not as crucial.maybe when wall inputs I allway leave blank the exterier sideing type insulations and only input R value in the walls.
03-22-2008, 09:57 AM
Is there a basement? Are the floors really insulated over the basement? Duct losses are greater in unconditioned spaces and should be insulated. If the basement is in the conditioned space it needs to be added. Why do you have so much shading on your windows? Are there awnings? Windows add allot of load. Don't count trees as shading. Not seeing the plan it's hard to tell if the inputs are correct.
03-22-2008, 10:09 AM
When I said 2 people per bedroom. I meant if you have 3 bedrooms. Include 6 people for the load.
Not list 2 people in the bedrooms, plus people in every room.
Didn't mean to mislead you.
03-24-2008, 10:23 PM
Yes I will have to admit I am very confused on the people/
Do add the people expected or the total of people in the house.
As a homeowner/ built this place, and contracted out the hvac to a reputable dealer, I still have questions about if they over sized my HVAC by a great amount. I appreciate everyones comments and will go to helping me have some piece of mind.
To answer another post, yes this is a ranch on a full basement and in order to get a building permit it had to pass RESCHECK which is a DOE (Department of Energy) home energy efficiency check. AS the builder it was a surprise to me when I went to get the permit. The only way it would pass was if the flooring was insulated, lowE double pane windows and doors and R30 attic insulation. I have seen numerous house being built at the same time that did not have insulated flooring over a full basement.
As for the shading most of the windows are on the front and rear which does have full length a eight foot covered porch on the front and rear.
03-24-2008, 11:35 PM
The most people that will be there on a regular basis will be 2 people per bedroom so you would only want to add 2 people per bedroom and leave the other rooms blank......unless your have in laws living with you permanently :D
03-25-2008, 11:30 AM
Just add 1 person per bedroom plus one (they assume two people in master bedroom) and add them to the living room. The load is considered during peak time of the day. People in the bedrooms don't add enough during sleeping hours to matter (system is over sized during the night). The load won't make much difference and you can prove it to yourself by changing the number of people in the program and watch the load change. I would double check how they entered the info into Res Check, I have Res Check but I only use REM/Rate, if you insulate the foundation to R-10 on the exterior it should be fine and not need floor insulation (there are trade offs in the program). If you plan on using the basement you will want to insulate the walls anyway. I would also insulate the basement ground floor, it will make a big difference in comfort. It sounds like you are building an unconditioned basement and it doesn't make sense to me. I would meet with the local code inspector and clarify the construction details.
I ran the data from your second load calc with the Carrier system product data.
At system cooling design conditions the system will produce about 50,000 btu/hr. in high speed. about a 10,000 btu/hr over-size. You have a modulating two-stage system, and if the ducts are correct, I would not worry about it.
For your heating design conditions, the system will produce about 42,000 btu/hr in high speed. This is right on for your design conditions.
Sounds like they sized it for heating, and you have a great system.
03-25-2008, 06:33 PM
Thanks Davo thats good to know. It's these little things that bug me. I do wish I had found this website during construction and it would have removed some of my troubles.
The system has performed flawlessly and I consider it to be very energy efficient.
Mbarson. I built a basement. It is not and was not intended to be finished. The only way to insulate the foundation for a unfinished basement would be to put Styrofoam panels on the exterior or frame the interior walls. Yes this would have worked except it is an unfinished basement. Georgia law will not allow Styrofoam below grade. Why TERMITES
03-25-2008, 08:26 PM
You might try to remove all the shading from the windows and see what the load is. I think the manual says to use unshaded unless there is a room with blockout curtains/shades always closed. The covered porch still allows reflected IR heat to enter. This might bring you closer to the 5 ton unit selected (when adding 20%) and reflect that the program is correct.
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