Author Topic: Is there a tool to estimate total home energy usage?  (Read 878 times)

kenmoremmm

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Is there a tool to estimate total home energy usage?
« on: September 16, 2021, 10:37:30 PM »
I'm building a house in the near future. Debating on solar panels and thus trying to decide if we should go with all electric or electric + natural gas. NG is commonly used in our area (Canadian Rockies) and it will get pretty cold here at times (down to -20F at for stretches). In the late spring to late summer, it's basically heat-off conditions similar to the Pacific Northwest. However, here it's very sunny.

I am curious if there is a tool out there that would allow you to enter house size, insulation, appliances, etc to see how much energy usage we'd be looking at.

We will have radiant floor heating and I understand that modern gas boilers are pretty damn awesome. However, there are electric boilers and there's a chance that, with solar, it would be better to go the electric route.

My builder, that lives in the same neighborhood as we will be moving into with a recently constructed house (to Step Code 3 requirements) says we might expect an average of $200/mo for gas and $60/mo for electricity for the year. So, if we assume that electricity is more $/energy-unit compared to natural gas, we could say $300/mo. Solar installs around here do not have much in the way of credits or incentives, so I think we'd be looking at $25-30k. Even the DIY kits available here are like $20k for the size that we'd probably need.

uniwelder

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Re: Is there a tool to estimate total home energy usage?
« Reply #1 on: September 17, 2021, 04:07:09 AM »
There shouldn't be any reason to use a boiler for radiant floors.  Get a water heater instead.  Circulation temperature should be less than 150 degrees, so a water heater will be more efficient and less expensive than a boiler.  When routing directly through a concrete slab, temps are usually less than 110 degrees, though I don't think thats the case for you, or not entirely.

I would go for the gas heat, rather than all electric.  In the US at least, using photovoltaic panels to heat water directly is not particularly cost effective, especially when a natural gas option is available.  With your temperatures, it doesn't sound like an air exhange heat pump option makes sense either, but perhaps geothermal could?  You'd likely have to go very deep for geothermal, so drilling several vertical holes or possibly laying loops a couple feet under the basement slab?  I'm assuming your slab will be insulated.

Looking at your rooflines from the previous house layout thread you had, its pretty complex.  Putting panels up there may cause them to be scattered about, meaning installation cost will be higher and less square footage available.  Not sure how cost efficient solar would be that far north--- what your payback period would be, maybe 15 years?  Looking at a map of annual sun hours in the Canadian rockies, its at the very low end compared to a US map of good places for solar.  If you wanted to put up panels to support the $60/month usage, that sounds reasonable, though again not sure how cost effective.

For energy usage, shouldn't your builder be able to provide all that info, at least on the heating end?  Not sure how the system is being sized otherwise if no calculations are being done.  Your house seems much too big and expensive to be relying just on general rule of thumb for heat loads.  Since you're spending so much money on this place, the most cost effective thing you might do is to consult an energy efficiency expert that can walk you through the various options of insulation, solar, heating systems, windows, etc to get the most bang for your buck. 


Systems101

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Re: Is there a tool to estimate total home energy usage?
« Reply #2 on: September 17, 2021, 09:40:42 AM »
However, here it's very sunny.

You may want to look at solar thermal rather than trying to do solar panels to an electric water heater.  The efficiency is MUCH higher (magnitude 70% vs 10%), and depending on where you are in the Canadian Rockies, it may be very effective (whereas it's not effective in places like New England).  A number of Passive Houses have been built in and around Whistler (some of which use solar thermal), if you haven't looked into those they could be a great source of lessons.


uniwelder

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Re: Is there a tool to estimate total home energy usage?
« Reply #3 on: September 17, 2021, 10:03:10 AM »
However, here it's very sunny.

You may want to look at solar thermal rather than trying to do solar panels to an electric water heater.  The efficiency is MUCH higher (magnitude 70% vs 10%), and depending on where you are in the Canadian Rockies, it may be very effective (whereas it's not effective in places like New England).  A number of Passive Houses have been built in and around Whistler (some of which use solar thermal), if you haven't looked into those they could be a great source of lessons.

I think thermal panels are typically around 60% vs 20% photovoltaic, not that it matters.  If the house is getting sun, the type of panels don't matter much, although photovoltaic will be a little more efficient in its range vs thermal because of the cold weather.  Cost per unit usable energy is what you should care about.

A friend of mine has a solar installation company.  He no longer installs thermal systems on residential homes.  The installation cost, along with required maintenance, make them non-competitive versus photovoltaic.  Up to about ten years ago, they were common enough, but in the last few years photovoltaic has come down so much in price that it needs to be a large commercial system to make any sense.  He can quote an installation for photovoltaic cheaper to simply use an electric hot water heater with the power output than for an equivalent thermal system, not that you'd want to do it that way, but as an example.

What can make sense in regard to thermal system is to DIY with old panels and place them somewhere you don't care about even heating, like a workshop or basement.  Just let the hot water pump through a concrete slab and reap whatever benefits you may.  I don't think this really applies to your situation.

Tester

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Re: Is there a tool to estimate total home energy usage?
« Reply #4 on: September 17, 2021, 11:17:50 AM »


I am curious if there is a tool out there that would allow you to enter house size, insulation, appliances, etc to see how much energy usage we'd be looking at.


The company building your house/the company providing the heating solution should propose the solution based on math and physics - they should have access to those tools and tell you: you need this amount of BTU because of X,Y,Z.

Some things (there are more, I just remember what was in the document for my house) they take into consideration are:
Location, wall/roof details, weather, orientation, window surface (and orientation I hope), type of heating solution...

If they don't give you that I would not trust them.

For a back of the envelope estimation you can use this https://www.calculator.net/btu-calculator.html

Papa bear

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Re: Is there a tool to estimate total home energy usage?
« Reply #5 on: September 17, 2021, 12:08:30 PM »
Itís called a Manual J calculation.  Good HVAC companies can do one for you ($$$) and Iíve also worked on some decent online calculators for an addition.

I used this:

https://www.loadcalc.net

You will need to know a lot of information to get an accurate output.  Everything from the orientation of your house, sunny days, number of occupants, r value of insulation in walls, floors, attic, u value and shgc for windows and doors, etc.  thereís a reason most places just take the sf and do a quick back of napkin calculation for sizing.  Thereís plenty of jokes out there for it!   2000sf? 80k btu furnace and 3 ton AC! Slap it in!


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