any test houses?

Unknown

Doug and all,

All of our heat and all of our measurements will only ever be good educated estimates. The problem with all the data is our main variable, the occupant. We can take the same house, change occupants, and get totally different answers. Age, comfort, activity, kids, thrify... etc etc all add into the mix.

Here in philadelphia , my data shows 4759 total degree days (20 year average) of those 800DD (17%) happen in months my heat is off. Others may run their heat those days. Mmmmm/

Add in the mix, DD are based on 65, about where I maintain my house. Other home owners are higher or lower. Then tell someone that your changes to their system will save them 20% and the thermostat is raised instantly from 55 to 75 (20% in their mind) and all the sweatshirts and sweaters are put away.

Now in my house I have a little problem with seperating my gas used for heat and my gas used for cooking. I can not use my summer month gas usage and subtract it from winter month gas usage... I cook outside using my propane BBQ most days :-)

So, how do we get exact data? I don't feel there is any exact way to get this data unless we use empty houses with computer controlled appliances and fans to simulate usage (this is the way we compared heating systems in our lab in Germany). Unless we do this then all we are doing is estimating.. and even that can vary 20-30%. So a house that shows 5 BTU per square foot could actually be anywhere from 3.5 to 6.5. A wide spread with no control... unless you are the occupant in each house.

wheels

[Deleted User]

Any test houses?

Interested how my buildings fare in heat loss. I have tried blower doors and infrared scans yet it seems that (esp one) house cools down faster and uses much more heat than it should. Anyone know if someone has come up with a formula to tell if your heat loss is normal?

For instance, if I hold the heat to say 75, all day (to get the mass in the house at a constant warmth) and then on a windless night at say 30 degrees (no solar gain) see how long it takes to go down to a specific temperature. I know there would still be some variables but wouldn't that give a pretty good idea how one house compares to others with heat loss?
I'm going to guess someone has done this or similar but I can't find any reference to it.

Doug_7

Comparing the Energy Use of Buildings

The best way to compare the energy use of buildings is to calculate the actual energy use per year per unit of floor area.

To compare the energy use buildings in the same city you can simply divide the energy use by the sq ft of floor area for each building. Example: Btu / Year / Sq Ft.

If you want to compare buildings in different climates, you have to bring heating degree days into the equation. Example: Btu / Year / Sq Ft / HDD.

This is commonly done in Europe. Many countries use kWh /year / sq meter of floor area. In Denmark they use liters of fuel oil / year / sq meter of floor area.

Attached is a 1997 DOE survey of the energy use of single family homes, which might provide a useful reference. The average is about 10 Btu / Year / Sq Ft / HDD. I will try find the full article.

Also attached is an Building Energy Rating Certificate from Ireland. Every building will be required to have one of these. The conversion from Btu to kWh is 1 kWh = 3412 Btu.

Comparing the Actual Energy Use of Buildings is a very important tool. My building uses less than 5 Btu / Year / Sq Ft / HDD. A super-insulated house will use less than one Btu / Year / Sq Ft / HDD.

Doug

Doug_7

Home Energy article

See full Home Energy article at:

http://www.homeenergy.org/consumerinfo/benchmarking-energy-usage.php

Doug

Doug_7

Bill - Does that work for you ?

Bill -

Blower doors and infrared scans provide excellent information on the common causes of excessive heat loss from buildings.

For the rating and comparison of the actual heating efficiency of houses, the Btu / Year / Sq Ft / HDD method works best.

Does this method work for you ?

Doug

Brad White_203

I started

to pull together such data for The Wall and my own edification, but getting that done was a Herculean task, especially with homes of various solar orientations.

Still, I think it is worth assembling that "BTU per SF per DD" even though there are limitations to the data.

Also, I have found that comparing two houses for even a given year had different results than the same two houses for another year (maybe the solar effect at work, among other variables). So I opt for no less than three full years of data just to even-out any unusual seasons, to minimize their impacts.

Doug_7

Btu / Year / Sq Ft / HDD method

Brad - Thanks for the reply.

I have used the Btu / Year / Sq Ft / HDD method to compare several different condominiums - some of very similar construction on the same street and some of vastly different construction. Also can compare to super-insulated houses.

This method is actually very simple to use - add up the annual fuel use, divide by the floor area and divide by the HDD's for that same year.

I have found that the difference in building heating efficiency shows up immediately and dramatically. The causes of the differences can vary widely - Insulation, Infiltration, Solar Orientation, Windows, behavior of occupants, as well as the efficiency and operation of the heating systems.

When one of two similar buildings uses 60% more energy, you can look for and find the reasons. When a dis-similar building uses twice as much energy, you can usually find these reasons also.

The difference in annual heating dollars can be huge - the opportunity is in identifying the changes necessary to save the money.

I don't think we will really start to improve building energy efficiency until we can measure overall building energy performance an a comparable scale.

Attached is another interesting article on this method of measuring building energy performance. A bit old but still very relevant.

Doug

Mark Custis

Doug

Do they open the windows or turn down the thermostats?

Brad White_191

Thanks, Doug

I have used the method among others for many years so just wanted to state the limitations as I have seen them. Especially so when nearly identical houses had such disparate gas usage and no direct cause was immediately apparent. Similar insulation (next to none, just the low-hanging fruit of the attic) and similar blower door tests.

I agree, it is a useful tool but with any comes with understanding the limitations.

My project was to compile a database (broader statistical sample) to get a better benchmark. There being such a disparity and finding enough common elements, I postponed the effort yet continue to collect data as I go. Likewise blower door test data.

Man, do we know how to have fun...

Doug_7

Applying the Btu /year / sq ft / HDD method

There is quite a bit of scatter in the daily data due to factors like sunshine, wind and the fact that the HDD is the mean of the daily high and low temperatures - not the average of the 24 hour temperatures.

For these reasons, I prefer to apply the Btu /year / sq ft / HDD method over an entire year. This averages out factors like sunshine, wind and the HDD calculation itself.

The attached chart shows our building before and after installing a high-efficiency boiler. It shows a 30% reduction in heating energy required. The correlation coefficient is up to 94% which is pretty good (I think).

It was more work than most people would do, to get the hundreds of daily meter readings necessary to generate the data points.

I think the best application of the Btu /year / sq ft / HDD method is to make macro comparisons of the annual energy use of the same building before and after major changes, or for comparisons between different buildings. Allows you to categorize different building on a Good, Better, Best energy efficiency scale for overall efficiency.

It is a useful figure, because if you multiply the Btu /year / sq ft / HDD figure by the cost of fuel and you have the annual heating cost.

I am very interested in the Passive House work in Europe: http://en.wikipedia.org/wiki/Passive_house

A Passive House requires space heating energy of 1 BTU per square foot per heating degree day. They use some very simple passive concepts, like the ground heat exchanger for preheating the ventilation air.

Regards

Doug

[Deleted User]

Sorry for the long wait for a reply, Thank you guys! I will have to chew on some of it for a while but it does get me a lot closer to what I was looking for.

Gordy

Unless the buildings have identical solar orientation, exposure to wind. Occupant habits being identical. Examples being habits of cooking, closing/ opening window treatments, bathing, laundry, thermostat settings,lighting usage,appliances. All the latent heat loads.

I don't see how a apples comparision could be a gauge even if the structures have similar heatlosses, square footage, and construction. Way to many variables.

Even if identical dwellings were sitiing 20 feet apart one could be shading the other, or one could be a wind break for the other.

Maybe I'm miss understanding the question or intent for the comparision.

Gordy

Doug_7

The reason for the question is -

The question is - How do you compare one house to others with respect to heat loss ?

The reason is to identify cost saving opportunities - identify the houses with unusually high heat losses - so the causes can be found and corrected to save money.

You do not expect the heat losses of houses to be the same - you expect them to be different. There are the opportunities.

If one house uses 5 Btu / year / sq ft / degree day and the other house uses 10 Btu / year / sq ft / degree day - you say Hmmm - why does that second house use so much more energy than the first house ? If we could find and fix the causes we could save a lot of money.

You look into the causes of high heat loss - such as insulation, windows and infiltration as well as the efficiency and operation of the heating systems. You can use diagnostic tools such as Blower doors and infrared scans.

If we are in the business of retrofitting buildings to save money on energy, we should be checking and comparing the overall fuel efficiency of these buildings on a comparable standard basis.

I am mainly working on larger multi-family buildings with cost savings potential of $5,000 - $20,000 per year - or more. It is not unusual to be able to cut heating bills by 30% or 40%.

It is basically the same idea as checking the miles per gallon of a vehicle - except it is much easier to improve the fuel-efficiency of a house than a vehicle.

Doug

Doug_7

An Investigative Tool

We are not trying to get exact data. We are trying to get relative data that shows approximately how efficient one building is compared to another building - corrected for obvious differences in floor area and climate. All data will vary - that is normal. You can improve data accuracy by collecting more data, which is why I recommend using annual fuel use.

The building and the occupants are a "system" and the occupants behavior definitely effect the results. So does sunshine. I posted a graph which shows the scatter in the data points. That does not mean that it is not worthwhile to measure how efficient the building is.

We measure the fuel-efficiency of cars. There are lots of variables - speed, stop-and-go, weight, tire pressure, driver habits and on and on. But it still provides a useful comparison tool. Buildings are a much larger cost investment and use more fuel than all the cars and trucks combined, but we still have no measurements of building fuel efficiency.

I posted an article on the buildings in NYC that used 24 BTU per SF per DD. A properly designed conventional house will use about 5 BTU per SF per DD. A super-insulated house will use 1 BTU per SF per DD. These differences are a long way outside any normal variation in the data due to any limitations of the method.

I think it is still worth assembling data on buildings of interest, even though there are limitations to the accuracy of the data. Wide variations in the data are due to causes. We are trying to find and correct those causes. Some causes are due to the occupant behavior, some are due to the structure and some are due to the heating system and how it operates.

If you think your fuel bills are too high, and want to look into it further, then assemble your "BTU per SF per DD" data and see where you stand. If it is 5 BTU per SF per DD then you don't really have a problem. If it is over 12 then your building is worse that half of the buildings in America and you have some real cost savings opportunities.

If you don't think your fuel bills are too high - then don't bother.

Doug

Glenn Morris

Btu's sqft/HDD

Hi - I am looking for similar info posted in this thread. Specifically a way to correlate a home's measurement with any Energy Star suggested rating for existing homes. Any data source for this or other ways to compare similar homes on the BTU's per Sqft/HDD would be appreciated. I realize these are very rough benchmarks.