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There are many possible reasons for this, but I cannot give you a useful answer without reviewing the actual file. Please open the file in OptiMiser and submit an error report using the red “!” button.
Currently there is one static default life time for each improvement category. This life time can be exposed and edited on the Improvement/Costs tab. Click on the “Columns: O and M” check box to expose the “Life Time” column. The default for the Upgrade DHW row is 13 years.
This does not imply anything about general results for window films in Las Vegas. The results will vary considerably from home to home depending on the orientation, window distribution, thermostat set-point, etc. I expect that many homes will see both energy savings and dollar savings.
The IECC codes were not developed solely to save home owners money. They have a broader mission that includes reduced environmental impact. Reducing SHGC’s will always reduce peak electricity demand through cooling reduction and that can mean less need for the utility providers to fire up older inefficient plants. Also, when you consider all of the inefficiencies in electricity generation and transmission, the improvement to this home may have reduced global energy consumption, despite having a slight increase in point of use consumption.
Moderator note:
It turned out that the model had the film applied to the SW and SE facing windows, but not the NE and NW facing windows. Because of the orientation of this house, the average daily solar intensity in the middle of the summer is actually fairly even across the four facings. However, in the winter, the solar intensity is much greater on the two southerly facings that had the film applied. Thus, the improvement impacts a little more than half of the eligible solar gains in the cooling season, while impacting almost all of them in the heating season. This combined with the lower efficiency of the furnace, relative to the AC, led to an overall energy loss. However, due to the higher cost of electricity there was still a small positive dollar savings. Applying the film to all window increased the savings.
To model radiant barriers, simply check the Radiant Barrier box in the ||Path popup for every attic section that has a radiant barrier installed. It does not matter how or where it is installed.
As is stated in the warning at the top of the Detailed Duct Efficiency Calculator, the calculator is a single set of controls that is used for each scenario. Any time you click a Detailed button from any of the duct control sets, you are opening the same calculator with the same set of controls. Each time you open the calculator, the controls are reset using relevant information from the main screen, based on the location of the Detailed button that you clicked. When you close the calculator the calculated efficiency can be copied back to the Efficiency control next to the Detailed button that launched the calculator. This preserves the results of the calculator. Unfortunately this means that if you made a mistake and need to revisit a duct setup, you have to specify it again. We do intend to develop separate control sets for each system in the future, at which time we will remove the warning message.
The TXV option should improve Delivery Efficiency. However, I have just discovered that the formula for the Equipment Efficiency Factor of TXV systems in ASHRAE 152 is only intended for use with fan flows between 200 and 400 cmf/ton. I will amend the calculations to revert to the standard Equipment Efficiency Factor when the fan speed is outside that range. In the mean time, simply leave the box unchecked, whenever you see that it decreases efficiency.
For this situation model the wall between the conditioned space and crawl space as and exterior wall under the Walls tab. Because the crawl space is unconditioned and the thermal barrier is at the insulated floor above it, the change does not impact the crawl space.
Is this the SHGC the only change made to the window? Was it made to all windows or just one facing? Did you model the overhangs correctly? Where are you looking at the savings? Are you sure that the U-factor doesn’t change? You called it a “low-e tint”. A low emmittance coating would reduce the U-factor.
If everything is modeled correctly, then this means that the loss of solar gains in the winter is costing more than the the savings attained through cooling load reduction in the summer. The balance between the two will depend heavily on orientation and shading, but also on the all the factors in the rest of the model that determine the length of the heating and cooling seasons and annual loads.
Did the SHGC change as well? Was the change applied to all windows? Are you looking at the savings for the window improvement only or for the entire package of improvements?
I’m a little confused by your description. Tell me if this is correct: The building has both a crawl space and a conditioned basement (or maybe conditioned space is the lower level of a split level home). One wall of the crawl space is adjacent to the conditioned basement/lower level and you want to insulate that wall. Is that correct?
