CRACK EMS HVAC CALC
Vida Hubbert
Note: This tool is provided strictly as a quick method of computing general size and value conditions. Square foot methods are considered rule of thumb for use in quick calculations. The exact thermal load can be determined by using a full heat load analysis.
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Thanks so much for the interest. The home is in MA. It is a 1,700 sq ft. cape (1956) which has had extensive air sealing and insulation upgrades. Blower door test was in at 1542 @ 50cfm before my last round of spray foam insulation which turned all cape dormer areas into conditioned space. Walls are a combo of Fiberglass/dense pack cellulose and rigid foam.
If I turn on my kitchen exhaust I have negative pressure in the home and my boiler back drafts down the chimney.
My manual J calcs came back with total heat gain of 15,692 BTUH
I was honest when entering the data and went for higher heat gain if anything.
I would like to locate my blower unit in the now conditioned triangle shaped space of 2nd floor dormer attic knee wall areas. It would be near the middle of the house and keep trunk line short....so I am not sure if friction losses come into play here. I also would like to use a minimum of flex duct (and use metal elbows if I do use flex for 90 degree bends).
Any help appreciated. I really think there is a market out there for Manual D consulting. Most of the HVAC guys I know just guess.
Bob,
A common duct guideline is that a 6-inch round galvanized duct can deliver 100 cfm and 7,400 Btuh of heat. That corresponds fairly well with Dana's calculation. My rule of thumb is 74 Btuh/cfm, while Dana's is 65 Btuh/cfm.
Dana, you based your BTU/hr calculations on the DeltaT across the furnace heat exchanger (supply air temp - return air temp). Would it not be better to consider the minimum desired room temperature instead? Taken to the extreme, if my desired minimum room temperature was 120F, the same as the exit air temp of the furnace, then the furnace would be incapable of heating the room regardless of the DeltaT across the furnace heat exchanger.
The Manual D spreadsheet from Acca.org is blowing up on the Friction Rate tab as it does not like the external static pressure of .15 in. W.C. that Carrier publishes as the ESP. Also it is clear the Manual D won't like the fact that I am not performing calculations on the entire house (there is a lot duct buried in walls & floors that I cannot see). Providing info on my furnace/ac while only running calculations for the basement's projected ductwork is likely not going to work unless I am missing something.
What I do in renovation to existing duct systems is: Start by visiting the site and measuring the existing system. System static pressure, airflow from all the registers, total airflow, delivered air temperatures, duct sizes, etc. I also collect information for a heat gain/loss calc. I talk to the customer to try and determine any existing comfort issues, like cold/hot rooms or slamming doors, how long the system seems to run during hot/cold times. This tells you how a system is actually performing, which is the most important thing for an existing system.
You do the heat loss/gain calc to ensure the equipment has enough capacity (10/10 so far it is way oversized) and then you give them a list of things to improve the system, like adding additional registers to uncomfortable rooms and fixing return issues, upsizing any ducts that are too small, repair any damage ducts you might have observed, airsealing existing ducts, maybe insulating long lines, balancing ductwork, etc. If you bring a good hvac tech along, he can check out the equipment and tell you if now is a good time to change it out or if it still has lots of life left. That's the process that should be taken. Measuring the existing system performance is key to a good retrofit design.
The latest version of Cool Calc Manual J is all about simplicity. We consolidated several screens and improved the map tracing capabilities. Users are now guided through the process from start to finish so even users with little experience can sucessfully complete a load calculation.
This Furnace Price Checker makes it very easy to calculate the cost of a new furnace and compare the quote from your contractors, to what other HVAC contractors are charging in your area, and see if you are getting a fair price, or being charged too much.
Loads calculations with the world-renowned APACHE engine allows for easy-to-use access to the most robust industry methods, which require (sub)-hourly calculations that account for the storage and thermal mass of construction materials.
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That is correct. The DP-Calc 5815 is a handheld digital micromanometer designed for fast and accurate differential and static pressure measurements, while the DP-Calc 5825 is a high-performance version that can also calculate flow and has data logging capabilities. Both models have various applications in HVAC commissioning and troubleshooting, testing and balancing, pitot tube duct traverses, static pressure measurements, pressure drop across filters, coils, fans, and diffusers, as well as environmental air flow testing.
The DP-Calc 5815 and 5825 micromanometers allow you to easily make HVAC pressure measurements. These robust instruments can be used with Pitot probes to measure duct velocity. The DP-Calc 5815 is a simple to operate, hand held digital micromanometer for fast, accurate differential and static pressure measurements. The high performance DP-Calc 5825 can calculate flow and has data logging capabilities.
The intent of the power calculator is to provide guidance for estimating the electrical and heat loads for typical operating conditions. It should not be used to calculate power or HVAC requirements. Instead, please use the appropriate installation guide to allow for proper allowances.
You MUST allow electrical and cooling headroom for unforeseen circumstances, component upgrades, and increased computational loads. Please allow for worst-case power conditions. Actual power consumption will vary from the sample workload used in the power calculator. These include, but are not limited to, the factors below. Each of these factors may cause significant differences in power consumption:
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