PHIUS Tech Corner, November, 2011, PHPP and Lighting, copyright PHIUS, 2012
PHPP and High Efficacy Lighting Prudence Ferreira, CPHC While the PHPP is a fantastic tool for calculating the energy balance of a building targeting the Passive House criteria, in some instances it is a bit limited, or more accurately, outdated. Once such example of its limits can be found in the Electricity Worksheet. Many of us have clients that utilize a high percentage of LED lighting, or a mixture of CFL’s, LED’s and incandescent. Yet, we are given only one cell that we can modify, cell J23 on the Electricity Worksheet to account for our lighting. This cell is labeled “Percentage CFL’s, however with a bit of arithmetic, this cell can be manipulated to produce results for any mixture of lighting. But first, we need to understand the underpinnings of the lighting wattage calculation. Here’s the low-­‐down: 1. Notice that when cell J23 on the Electricity Worksheet is set at 0%, cell H23 report 60 watts. This is the default wattage assumed with 0% CFL’s 2. Now change cell J23 to 100% and notice that cell H23 reports 11 watts. This is the default wattage assumed for 100% CFL’s. A look at the PHPP Manual tells us the assumed average lumen output here is 720 lumens. 720 lumens at 11 watts equates to 65.45 lumens/watt for CFL’s, whereas 720 lumens at 60 watts equates to 12 lumens/watt (this is on the efficient side for incandescent which typically range from 5-­‐15 lumens/watt) 3. Following row 23 across the page, we can see the following calculation: Demand * Utilization Factor * Frequency * Reference Quantity = Useful Energy kWh/yr used * Electric Fraction = Electricity Demand Let’s take a closer look: • Demand (Watts) =11*J23+60*(1-­‐J23). In English this breaks down to assumed wattage for CFL (x) the percentage of CFL (+) assumed wattage for incandescent (x) percentage incandescent • Utilization Factor -­‐ Is the lighting inside the thermal envelope? • Frequency – For lighting the PHPP assumes 8 hours per person and day or 2,920 hours, which the PHPP lovingly converts into 2.90 kh/(P*d) or kilo hours per person and day • Reference Quantity (ie Occupants) – this carries over from your Verification worksheet and can change depending on whether you select “Verification” or “Design” mode and whether your project is utilizing less or more than 35m2 of TFA per person • Useful Energy – This is the product of all preceding factors multiplied together. • Electric Fraction – How much of the fuel to power your lights is coming from electricity? • Electricity Demand-­‐ Total demand associated with your lighting Passive House Institute US | PHIUS
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PHIUS Tech Corner, November, 2011, PHPP and Lighting, copyright PHIUS, 2012
So now that we understand what is being calculated, we can get back to the task at hand: Accounting for LED’s and other lighting types that have higher efficacies than 65.45 lumens/watt. Here’s how: 1. Verify the lighting schedule with design team and owner 2. Calculate the average lumens per watt for the project a. Example: Your dream client is using the latest and greatest LED light fixture achieving 100 lumens per watt for 75% of their overall lighting, the remainder is CFL’s performing at 60 lumens/watt. 100 *0.75 + 60 *.025 = 90 lumens/watt average. 3. Adjust the percentage on cell J23 to produce the watts in cell H23 that correspond to our example. a. 720 lumens /90 lumens/watt = 8 watts b. Adjusting the percentage up to 106% in cell J23 yields a result in H23 of 8 watts 4. For your use, the PHIUS Technical Committee has created a Lighting Calculator to assist you in deriving your desired wattage result for H23 . The caclulator allows entry for up to 20 different lamps/bulbs. You will only need to know 1) rated lumens, 2) rated watts, and 3) quantity of lamps/bulbs installed for each type of lamp/bulb. The calculator includes the example noted above for reference. 5. Download the Lighting Calculator here: http://www.passivehouse.us/passiveHouse/LightingCalculator.xls Additional Notes: For circumstances where the lighting is being used for more than 8 hours per day per person, simply unlock the worksheet and adjust the value in cell N23, adding a comment for the reviewer and including supporting information in your PHIUS+ submittal. Please be aware that the lighting electricity demand calculation in PHPP is a “rough” entry and doesn’t go into the level of detail that a lighting consultant might like to see. For instance, it doesn’t take into account high use areas versus low use areas, daylighting, actual lumens out of fixture versus rated lumens out of lamp, etc. Given these limitations, please use the tools at your disposal to calculate lighting electricity demand as accurately as possible! Passive House Institute US | PHIUS
110 S Race Suite 202 Urbana Illinois 61801
217.344.1294 www.passivehouse.us