Average lighting, appliance and plug loads for PV sizing?
In doing some energy modelling for a future single-family net zero residence (in Canada), I am running into the problem of trying to guesstimate what the total lighting, appliance and plug loads will be. Because it can be different with every specific family, I’m wondering if anybody has any links or resources they can provide that offer average values for these loads that one can use. I will calculate the heating, cooling and hot water loads separately, but am hoping somebody has some suggestions for those remainders. Here are some basic parameters that I would think would apply, so let me know if your assumptions deviate drastically.
– Family of 4
– All family members work or attend school outside the home during the weekdays
– Whole house LED lighting
– Typical ducted 220V dryer
– Typical full suite of energy-star rated kitchen appliances (fridge, separate upright freezer, dishwasher, range/oven, microwave)
BTW- I found Martin’s old article on the issue (https://www.greenbuildingadvisor.com/blogs/dept/musings/tackling-plug-load-problem), but it didn’t seem to have any hard values on what figures could be used as averages for starting points, but did highlight the challenges in doing so.
Anyway, any help would be great to see if I am on the right track. Even rule of thumb guides that people use would be helpful. Thanks very much!
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Replies
Burke,
Rule of thumb: A net-zero energy house requires a PV array rated at between 4 kW and 9 kW.
Big range, I know. Every family is different. Are you a conserving family, with a minimum number of gadgets? Or do you have a chest freezer, a couple of refrigerators, and two big-screen TVs that stay on for 6 or 8 hours every night?
I assume that you are living somewhere now. Look at your electricity bills to get a rough idea of what you are using now.
Thanks Martin. I guess really going appliance by appliance, device by device, light by light and tallying loads is the only way to do it. Because my current home' energy bills lump heating, hot water and all other energy into one bill (we are 100% electric), this doesn't help me isolate our plug, light and appliance loads for sizing a PV system for our new house under design. Thanks for the input regardless!
What about just using your shoulder-season usage to get plug loads plus water heating plus lighting? Then calculate heating/cooling separately.
Burke,
Charlie's suggestion is a good one. It's the standard approach if you are trying to separate plug and appliance loads from heating and cooling loads.
However, why do you find it necessary to separate these loads? If you are planning to build a net-zero-energy home, I assume that you will be building an all-electric house.
I admire your attempt at accuracy, but it's important to remember that there are a lot of variables. Predicting the energy use of a new home is difficult. Looking at your old bills, and perhaps lopping off a little to account for the fact that your new home will be better insulated and tighter than your old home, may be all you need to do.
Good thoughts both- thanks. I guess I may be trying to get it more precise than I need to, but because the new house will be a substantially different size and have far improved insulation levels, and because I may be using a heat pump water heater instead of electric resistance, and because we will have all different appliances and exclusively LED lighting, it seems like the differences may be substantial enough that they will be hard to predict. But, perhaps I can use existing data and just guess at a reduction factor. Designing an array layout that will allow for adding more modules later without looking goofy or unbalanced will need to be a consideration. Thanks!
Burke, I agree, you can't just use your current bill, since the new house will be so different. I'd suggest using a watt meter on as many things as you can for a week or so. If you're going to buy a new fridge or freezer you can use the manufacturers annual number. I can share my number, 3500 kwh/yr for a family of 2, lights (mostly led or CFL's), & plug loads. No elect dryer. Elect stove, refer, freezer. The freezer was not very good, & probly used 700 kwh/y. I was able to do what Martin & Charlie suggested, but I had gas & elect separate.
Thanks for the comparison number, Brad! I'll use it to see if I'm in the right neighbourhood after I've sorted it out. I've been working on a spreadsheet to help me figure these appliance, plug and lighting loads, so maybe I'll post it here when it's finished.
If you want a generic number to get you started, PHIUS has a calculator: http://www.phius.org/software-resources/wufi-passive-and-other-modeling-tools/calculators-and-protocols
Scroll all the way down to the bottom and download the "PHIUS+ 2015 Single-Family Calculator"
You only need to input the iCFA (interior conditioned floor area) and number of bedrooms. Then check the "Televisions + Misc. Elec. Loads (kWh/yr)" section. Keep in mind that this number is designed for passive house certification purposes, not for accurately predicting a specific individual family's use. But it at least gives you a starting point.
I recommend you follow Charlie and Martin's advice. If your new home will have similar appliances and electronics as the new home you can use your Base Load numbers from your existing home. For HVAC power usage you could use the energy modeling numbers. My last home was net zero electric. I sized my PV system based on the previous 3 years power usage.
Brendan- great resource, thanks! I will use that, in conjunction with my former billing from the summer months of our current house, and see how they "jive" with one another. From there I should have a pretty good sense of where I stand.
Hi all. As promised, here is the energy loads worksheet I have created. It is by no means perfect, but feel free to use and modify it as you see fit. I have left the data that I have inputted so far (customized for our family and planned residence) for interest's sake (and so you can complain to me if I have made any major errors so far!). It does have some site to source factors, and some lbs of CO2/energy unit conversions which I had acquired at a renewable energy course ages ago, but which are likely outdated. Feel free to comment on them if you know they are out to lunch!
Burke,
Where are you building? You are on the east side of the Island aren't you?
That's right Malcolm- in Nanaimo.