Plug and process loads are one of the most important factors for LEED points for energy, but they are often overlooked. This category includes everything that is plugged into a wall and other permanent equipment like elevators, walk-in refrigerators, and ventilation fans that are not part of an HVAC system. (It does not include lights and water heating)
The reason why this category is often overlooked is because in the energy model you are required to put in the same energy use for plug and process loads in the proposed model (actual building design) and the baseline model (hypothetical building designed to minimum code).
LEED points are calculated as the percentage difference in energy cost between the proposed model and the baseline model. So if the plug and process loads stay the same in both, why do higher plug and process loads reduce LEED points for energy?
When the energy use from plug and process loads increases, the total amount of building energy cost for both the proposed and baseline model increases. Thus as the total energy cost increases for both models the energy cost savings will be smaller percentage of the total energy cost, decreasing the LEED points you will earn.
Here is an example to demonstrate this point:
You may be thinking that reducing the total plug & process loads by more than 50% is probably not easy, but later on I will show you how it’s possible.
So, many projects can directly earn 1-2 LEED points from plug & process load reduction (Every 2% increase in energy cost savings between the proposed and baseline model equals 1 LEED point in LEED v4.0)
Assuming the plug and process loads are located in the building, they produce waste heating which reduces the amount of heating that is required from the HVAC system for both the proposed and baseline models. In projects that use heat pumps, which are 3-4 times more energy efficient than electric-resistance heating (as talked about in part 1 of this guide), increasing plug and process loads can significantly reduce energy cost savings, which means less LEED points.
Here is how:
The total energy cost savings are derived between a proposed model and the baseline model. So, when a building uses heat pumps which produce heat that is 3-4 times cheaper than electrical resistance heating, you get more cost savings from heat pumps over baseline than any other electrical savings measure (like using more energy efficient water heating and lighting).
However, this also means that when you increase plug and process loads and significantly reduce the heating use, the energy cost in the baseline model for the inefficient resistance heating also drops by a lot (heat from plug and process loads is equal to electric resistance heating cost). But it doesn't drop the heating cost by the same amount for the heat pumps in the proposed model because the heat from heat pumps costs much less than heat from electrical resistance systems. And since we're comparing the amount of total energy cost between the electric resistance baseline and the heat-pump proposed, this difference will decrease.
Here is an example to illustrate this point:
Example Explanation (skip if everything is already clear)
Higher plug & process loads reduced the heating costs by $15,000/month from $40,000/month to $25,000/month in the baseline and only by $3,750 from $10,000 to $6,250/month in the proposed, due to the heat pump used being 4 times more efficient. The total energy cost in the baseline remains the same when you increase plug and process loads because the heating from electric resistance has the same efficiency as plug and process loads, so the cost increase in plug and process loads becomes the cost decrease in electric resistance heating. The higher plug and process loads only reduce the heat-pump heating by $3,750/month compared to $10,000/month from electric-resistance heating in the baseline. That means the total building energy cost in the proposed increases when plug & process load cost increases, whereas the total building energy cost in the baseline remains the same. And when the proposed energy use goes up compared to the baseline, we end up with less energy cost savings, and less LEED points.
The equal totals in the baseline models in both situations may make you mistakenly think that we are comparing totals in terms of heat savings (instead of cost savings) because we traded heat costs with the heat generated from plug and process loads. And that could make you think, “Since we’re also saving the same amount of heat with a heat pump, why did the total in the proposed go up?”
If this confuses you, remember that cost is not based on the amount of heat used, but the amount of electricity used to make that heat. It takes heat pumps 3-4 times less electricity and cost to generate the same amount of heat as electrical resistance systems. That means the heat cost reduction with higher plug and process loads is less with heat pumps ($3,750 reduction/month) compared to electrical resistance ($10,000 reduction/month), which doesn't offset the higher cost of "plug and process load" equipment use, as electric-resistance heating does. These smaller heating cost savings increase the total energy cost in the proposed model.
So how do these two factors affect the number of LEED points for energy on a project?
On an elementary school project I worked on, doubling the plug and process loads from 13% to 26% resulted in a 3-point reduction in LEED points due to the decreased heating use. But higher plug and process loads also increase cooling use and increase total savings (This works in the same way that decreasing heating from plug and process loads decreased total savings in the last example). However, this effect is not as significant as the effect from increased heating: on this project, the extra cooling use only increased the LEED points by 1.
The effect from increasing plug and process loads overall reduced the LEED points by 2 points. The dilution of total savings through increased plug and process load cost further reduced the school’s energy LEED points by 1 point. The net loss in LEED points on this project for increasing plug and process loads was 3 points.
Now that you know how important plug and process energy use can be for LEED points, the question is how do we reduce the energy use of this category? There are three ways:
Do a careful job documenting the actual plug and process loads in the project. In most of the projects I have worked as an energy modeler, plug loads were not provided to me by the design team nor the client. This is a typical situation and in this case energy modelers typically assume that 25% of the total baseline energy use is plug and process loads. This is an unofficial default in LEED: energy modelers know that if they use this 25% default, they will not likely be challenged by reviewers to provide documentation on the actual plug and process loads in the building. The problem is that 25% of the total baseline energy use is much higher than many projects use, if they are using energy efficient equipment. Therefore, documenting the electrical equipment is the greatest way of reducing plug and process loads, even by 50% or more.
Lower levels of plug and process loads than 25% of the total baseline energy use should be documented, since there is a high chance that below this number the LEED reviewers will ask for complete documentation. Preparing the documentation for plug loads (not process loads) requires working with the client to specify them for the energy modeler. By educating the client on how important plug and process loads are for total LEED points, you can hopefully convince them to choose equipment, such as computers, earlier in the design process.
Once you know all the specific equipment, you need to make a list of plug and process loads, which needs to include the average power consumption (average watts; what is listed on equipment is maximum) multiplied by the daily hours of use to get the daily power consumption for the plug loads.
https://www.siliconvalleypower.com/residents/save-energy/appliance-energy-use-chart
Talk with clients about ways to reduce plug and process loads in the project. One of the easiest ways to do this is to use more efficient computers and monitors. Talk to clients about the possibilities of using laptops instead of desktops (for highest energy savings) or at least using efficient desktops such as energy star-rated models. Make sure to document the average power consumption (average watts; what is listed on equipment is maximum) of these more efficient plug loads and their daily hours of use, so that these savings can be included in the energy model.
In residential projects LEED pre-approved energy star appliances directly reduce the plug and process load cost in the proposed model.
This is an exception, as in all other building types they have to be counted equally in both the baseline and proposed models, as you have seen in the previous examples, unless you ask LEED for special approval. This includes Energy Star equipment or equipment that is more efficient than average.
In terms of asking for special approval, I have not heard of other energy modelers succeeding in this. But with the link below you can find out more specifics on documenting a reduction in plug and process loads for LEED approval:
https://leeduser.buildinggreen.com/forum/industrial-or-non-regular-process-load
Aaryan (R-yahn) is an American daylighting innovator, math geek, and energy & daylighting educator and consultant.
He has over 10 years experience in energy & daylight modeling and consulting for LEED and other certifications.
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