Calibration

Using OptiMiser For IRA HOMES BPI-2400 Audits

Hi All! As you probably know, OptiMiser is a DOE-approved modeling tool for IRA HOMES programs. If you are wondering how to complete the modeling for these jobs and get HPXML, you've come to the right place. Please check out this forum and post questions if anything's unclear.

Make sure to use the built-in error reporting function in OptiMiser if you have any project-specific questions - it's by far the best way to get help since it sends our team all the logging they need to dive into any issue.

Also make sure to check out the videos on this site, tooltips in the OptiMiser (hover over any control) and the page help in OptiMiser (hover over any control and hit F1 or right-click then "Help").

How to calibrate using BPI-2400

OptiMiser has BPI-2400 compliant auto-calibration built-in. So, every audit you do where you enter historical bills is basically a BPI-2400 audit, as long as you check the Enforce BPI-2400 box before running calibration. (BTW, make sure you let us know you are participating in an IRA HOMES program so we can get you all the latest information - replying to your setup email is a good way to do that.)

OptiMiser's auto-calibration aims to eliminate manual true-up in most cases. The basic idea is to
1. enter utility bills
2. work through the Wizard interface entering information you know and NOT making guesses
3. use the calibration range controls to give OptiMiser reasonable freedom to calibrate*
4. hit the calibrate button and watch OptiMiser snap the base model in line with historical usage
5. check results to ensure BPI-2400 compliance

*What are reasonable calibration ranges? For the most part, this is a not a difficult or mysterious issue. BPI-2400 has range limits for some parameters defined. Where it doesn't, OptiMiser establishes mins and maxes based on studies or our (vast) experience. Within those highs and lows, your job is to set reasonable ranges based on observations and experience. For example, in an attic, you will have observed an insulation depth, but it probably varies across the attic space. What's the best single value to enter in this mathematical model? No one knows. So it's appropriate to enter a range of depths that you observe in that space, and let the calibration identify the best-fit value that, along with all your other observations, most aligns with historical usage. Similarly, you may have a boilerplate system efficiency but without a tested value you should certainly use a range (OptiMiser will suggest a range based on the vintage you enter).

To see how you're doing with calibration (BPI-2400 status) go to the Calibrate->Calibration Results page in the Wizard (BTW, you should ALWAY use the Wizard UI). The Action column in the table there will tell you what changes need to be made to reach calibration. Be sure to also check the Calibrate->BPI-2400 page to make sure there are no input violations. If you are having trouble calibrating particular files, we're happy to help with a few. It's best to ask your questions using the built in error report feature (red exclamation mark). That system will send us your project files and other diagnostics, which will help us understand what you are experiencing.

If the auto-calibration has trouble getting the model to match the bills, here's a post on some additional steps you can take: https://optimiserenergy.com/forums/topic/calibration-primer/

Calibration Primer

When a model fails to calibrate, it's time to look for errors and revisit assumptions. Although calibration helps to ensure accuracy of savings estimates, you never want to go to extreme lengths to calibrate a model. Don't modify inputs beyond what could reasonably represent reality. Some models just won't calibrate for a variety of reasons from abnormal billing records to unusual usage patterns to physical circumstances in the home that can't be observed or modeled. With that in mind here some things to consider when reviewing a model that isn't well calibrated

Utility bills - errors can lead to poor estimates of weather normalized usage for all end uses

- Double check fuel energy units
- Check for other data entry errors (e.g. dates usages offset by 1 month, missing digits)
- Remove any bills with abnormal usage by checking the Omit box
- Make sure there is adequate and accurate representation of base load bills
- Base load usage is not constant. DHW and lighting loads have pronounced winter peaks. If you are using high/low bill entry it may improve results to pick an average base load bill rather than the absolute lowest.
- Incorrect base load representation will impact heating and cooling load estimates. 

Heating loads - check these inputs for poor heating calibration

- Check for error/double-counting of envelope areas
- Floors above unconditioned basements and crawlspaces should not be listed separately as frame floors
- Attics should only be used to describe boundaries between conditioned space and unconditioned attic buffer space
- Vaults should only be used to describe roofs over conditioned space
- Default wall area calculations should be reviewed for split level houses, houses with finished attic space, and other unusual constructions
- Use/expand thermostat temperature ranges
- Thermostat set-point ranges can be used to account for variation in how the homeowner uses the thermostat as well as inconsistency in how the home is conditioned. Duct leakage and registers that are closed or blocked by furniture may cause some rooms to be only partially conditioned, reducing loads.
- Use/expand system efficiency ranges
- Double check system sizing. Be sure you have entered sizing in the correct units.
- Review conditioning selections for crawl/basement
- On the detailed screen there are editable assumptions for the basement average temperature, which is often lower than the upper floors. If you edit these temperatures, be sure to also consider how the temperature will change with any added insulation on the improved side.
- Be sure that duct location specification accurately represents total distribution of ducts.
- Note that for multi-story houses a selection of Attic, Basement, Crawlspace, or Slab automatically places 35% of supply ducts in conditioned space. >

Cooling - check these inputs for poor cooling calibration

- Check for error/double-counting of envelope areas
- Floors above unconditioned basements and crawlspaces should not be listed separately as frame floors
- Attics should only be used to describe boundaries between conditioned space and unconditioned attic buffer space
- Vaults should only be used to describe roofs over conditioned space
- Default wall areas calculations should be reviewed for split level houses, houses with finished attic space, and other unusual constructions
- Use/expand thermostat temperature ranges
- Thermostat set-point ranges can be used to account for variation in how the homeowner uses the thermostat as well as inconsistency in how the home is conditioned. Duct leakage and registers that are closed or blocked by furniture may cause some rooms to be only partially conditioned, reducing loads.
- Use/expand system efficiency ranges
- Double check system sizing. Be sure you have entered sizing in the correct units.
- Check window area, treatments (esp. bug screens), and overhangs
- Bug screens, overhangs, and other window treatments can significantly reduce cooling loads.
- Be sure to specify roof/wall colors that are very light or reflective.
- Be sure that duct location specification accurately represents total distribution of ducts.
- Note that for multi-story houses a selection of Attic, Basement, Crawlspace, or Slab automatically places 35% of supply ducts in conditioned space. >

Mixed Heating Appliances

OptiMiser now offers direct support for multiple fuel types. On the Utilities tab, select “Multiple Fuels” in the Fuel Type control and then open the Multiple Fuel Entry popup. You can choose Start and End dates (preferably spanning at least one year) and then enter total usage for each fuel. The instructions below are still useful, if you feel that you can accurately describe multiple periods of combined usage.

At this point the utility analysis can handle electricity plus any one fuel. Simply specify on the Utility tab, whether the home uses Fuel Heat, Electric Heat, or Dual Heat. That will inform the utility analysis where to search for the heating signal. In the situation you describe, the analysis would get the heating, cooling, and electric base load (i.e. appliances) information from the electric bills and the one fuel base load information from the fuel bills.

For multiple heating fuels. you can work around this limitation by converting usage for a second fuel to the same energy units as the primary fuel. The tricky thing about doing this is that the delivery schedules will probably be different. You will probably have to combine multiple bills to achieve a period with known total usage. You may even need to combine all of them into one period covering the entire heating season. It would be helpful to read the section on "delivered" fuels in the Utilities help. Here are the Btu equivalents for a selection of heating fuels:

Natural Gas (MCF) - 1,025,000
Natural Gas (Therm) - 100,000
Natural Gas (MBtu) - 1,000,000
Electricity (kWh) - 3,412
Propane (CF) - 2,539
Propane (Gallon) - 91,330
Fuel Oil (Gallon) - 140,000
Wood (Cord) - 20,000,000
Wood (Pound) - 8,000
Pellets (Ton) - 16,500,000
Pellets (Pound) - 8,250
Kerosene (Gallon) - 135,000
Coal (Ton) - 28,000,000