If you're wondering about the kind of experiments that are used to determine green roof efficiency, then you might be interested in Dr. Liu's experiments. Dr. Liu currently works in Ottawa measuring the amount of heat transferred through the greenroofs at each month of the year. During winter the green roof doesn't make much of a difference when compared to a regular roof. However during the rest of the year the green roof reduces the amount of heat transferred through the roof.
" The average daily energy demand for space conditioning caused by the reference roof system was 20,500 BTU to 25,600 BTU (6 kWh to 8 kWh). However, the green roof system's growing medium and plants modified the heat flow and reduced the average daily energy demand to less than 5,100 BTU (2 kWh)-- a reduction of more than 75%."
quoted from Dr. Liu ( National Research Council Canada, Ottawa)
From: Dr. Lola Justice
From: Dr. Lola Justice
7 comments:
Wow, the green roof really cut down on heat transfer alot. I bet that made the energy bills for the building alot cheaper. Any ideas how much money that would save? I am seriously thinking of suggesting that city council look into a getting a green roof on City Hall.When I got involved as financial advisor on this project I was worried about the amount of money it would cost. Now I see that it is going to save us money.
Mr McPhee
I guess the green roof might cut down on heat costs but how is it going to hold all that weight? and anyway you are going to have terrible leakage problems with water streaming down the walls. I'm sorry but I'm just fed up with all these new fangled notions - we have done fine with the kind of roof we have for the last forty years.
Mr. A. Garnett
Hi Mr McPhee
Average cost would be $175.2 for a regular roof.
Average cost would be $43.8 for a green roof.
I know that this doesn't seem like a big difference but if you took that into prospective for 10 years, than the saving is larger.
Thankyou,
Dr. Lola Justice
Dear Mr. A. Garnett
There wouldn't be any leakage problems because the green roof has a water proof barrier. I will post you some more information on this as soon as I can.
Thankyou,
Dr. Lola Justice
thanks Dr Justice,
I would love to take a look at your calculations. Looking at your original information on your post I am thinking we could get substantial savings. I'm not sure of the time period you have used for your calculations. I need to know the number of kWhs transferred through each type of roof per day and the value you are using for the cost of 1kWh. I am very excited though as I really believe this would be a good idea for city hall.
Mr Mc Phee
Dear Mr Mc Phee,
This pricing is for 1 year. I used 6 cents/KWH in my calculations.
Thankyou,
Dr. Lola Justice
Dr Justice and Dr Hudson,
you know I think you dropped the 2007 prices in there instead of 2020. A slip of the pen I'm sure. Remember energy prices have sky rocketed and your green roof is really going to save us lots of money in 2020. Energy prices are 100X greater than they were in 2007.
That means that we're talking $6 not 6c
That means we're saving the difference between $17,520 and $4380 THATS $13,140/year! substantial - what was the area in the roof in the study you read about?
I am very excited about this!
Dr McPhee
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