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Please check this post and let me know if it answers your questions:
Hi Bradley – Are you trying to move the thermal barrier from the floor to the roof to create a conditioned attic out of a previously unconditioned space or is the attic already conditioned and you are just looking to add insulation?
Apologies for the delayed response. We had a temporary malfunction in our notification system.
If you are installing a new heat pump to serve as both a heat source and cooling source, then you will have to specify it separately on both the Heating and Cooling tabs . You will then need to override the cost setting to split the cost of the single system between heating and cooling. To see the total SIR of replacing both the old furnace and the old AC, check only the Heating and Cooling improvements on the Details table and review the Package Total SIR at the bottom.
Apologies for the delayed response. We had a temporary malfunction in our notification system.
My understanding is that pressure pans are only suitable as a diagnostic tool and their readings cannot be used to drive a model of duct leakage. You will have to use the generic leakage description selections in the Leakage control.
I assume that you are referring to controls on the Duct Efficiency Calculator. Unfortunately we currently only have one instance of that calculator and it is used for all systems. Therefore the control specifications cannot be saved. Please note the warning message at the top of the calculator and that the button is labeled “Copy Results and Close Window”. The efficiency results will be copied and saved to the Delivery Eff controls on the main interface. If you are only concerned about storing the LTO, there is actually a way to do that on the main interface. Choose “Measured (cfm25)” in the Leakage control and a control labeled cfm25 will appear to the right. This leakage along with the other simple controls on the main interface are fed through the full calculator to generate and efficiency estimate, when the Edit? box is not checked. You will also note that if you set that control and then open the full calculator, that your setting is automatically imported.
OptiMiser’s utility analysis can handle delivered fuel. If all the deliveries are “fill-ups” and you have records covering a full year of usage, then you can often get an analysis that passes the BPI standards and can be used for auto-calibration. Even if the bills are not sufficient for auto-calibration, OptiMiser can provide a weather normalized annual usage that can be used to hand calibrate the model. More information about how to enter the fuel bills is available in the OptiMiser Help.
OptiMiser uses a single zone model, so it is fine to combine systems in one set of controls. Any set of systems that have the same fuel and type of distribution system can be combined into a single described system as follows:
- Set the % Total control to the proportion of the building load met by the combined systems
- Set the Capacity to the sum of the individual capacities
- Set the AFUE to the capacity weighted average of the of the individual systems.
- For two systems this would be AFUEAvg=(AFUE1*Cap1+AFUE2*Cap2)/(Cap1+Cap2)
- Set the Delivery System controls as though you were describing a single delivery system.
- Duct Leakage should be set the the sum of the leakages though the individual systems.
- Duct Insulation should describe the area weighted R-value of insulation on the ducts.
If you have flexibility in making your combinations, try to combine systems that have the most similar distribution systems.
EDIT: Wood, pellets, and coal are now available as options in the Fuel control for heating systems. Unfortunately we do not yet have direct support for sidearm water heaters, so most of this work around is still necessary.
This will require two workarounds and probably a little research on your part. The workaround is for using wood as a fuel. We hope to build direct support for wood, but for now you will have to hijack another fuel.
Using wood fuel:
- Set heating system fuel to a type not used by any other system
- Choose a system type with the appropriate delivery method (Boiler, Furnace, Direct Heater)
- Set the efficiency to the known efficiency of the system. If unknown look up system in http://www.epa.gov/compliance/resources/publications/monitoring/programs/woodstoves/certifiedwood.pdf or choose appropriate defaults from RESENT standards http://www.resnet.us/standards/RESNET_Mortgage_Industry_National_HERS_Standards.pdf.
- Go to the Envelope/Building tab and click the More button to the right of Electricity Prices
- Set the units on the selected fuel price to $/MBtu.
- Set the fuel cost to that of the wood source using the conversion 1 cord = 20 MBtu or 1lb = .008 MBtu
The second workaround will be for the water heater. You didn’t give me any details on that, but assuming that it works like a typical side-arm water heater, you can use the workaround posted in this thread from our old knowledge base system http://help.optimiserenergy.com/article.aspx?cid=4997&aid=12773. The only problem that I foresee with that workaround is that the AFUE of the furnace is based on the efficiency of the air-based heat exchanger and the recovery efficiency of the water heater would be based on a separate hydronic heat exchanger. I don’t know how to estimate that difference.
You will want to use the same fuel that you select for the furnace and you will need to estimate the annual load split between this system and the backup system that operates during non-heating seasons.
The short answer is Yes.
The modeling engine is constantly evolving, but we routinely run it against the BESTEST suite of tests as well as the various systems tests in the full HERS accreditation series. We have not submitted our current version for accreditation because we are waiting on RESNET to resolve of an inconsistency in the latest revision of the HERS Standard. We also are not currently marketing OptiMiser for HERS ratings, though we may in the future.
The location of the radiant barrier control on the || Path popup, does not indicate that it is modeled in parallel with the insulation. Most of the components specified on that popup are components that are part of each path in the parallel path calculator and thus run in series. The only things that vary across the three parallel paths are the cavity insulation and joists.
We model attic using a method published in the ASHRAE Heating and Cooling Load Calculation Manual. This method generates an effective thermal resistance of the attic space and roof assembly, which is then modeled along with other ceiling components and the insulation as a single envelope component. This contrasts to the method of modeling the attic as a separate zone. The ASHREAE method relies on resistance numbers generated by ASHRAE for different combinations of ceiling R-value, presence of reflective surface, ventilation rate, and roof absorptance. The method does not specify a particular installation method for the radiant barrier.
