
In the northeast, we spend a great deal of our total energy (note this is not just electricity) on home heating (about 44% of the utility bill is heating & cooling). In other locations, home cooling is the major expense. In some locations, both heating and cooling are required to ensure our comfort. How much energy we will need is obviously weather dependent. The colder (or warmer) a location is, the more energy will be needed, and if the winter (or summer) is long and has many cold (hot) days, then more energy is needed. We can express this impact mathematically using heating degree days (HDD) for our heating needs and the summer equivalent cooling degree days (CDD).
HDD and CDD
How much energy is needed to heat (or cool) your home is dependent not only on how many days that heating (or cooling) is needed, but also how cold (or hot) it is outside. On a very cold day, you will need to use much more energy than on a slightly cool day. We can quantify this by examining the temperature difference and for how many hours it is needed (we need more heat in the evening/early morning or more cooling mid-day). Heating is needed < 65o F (<18o C), We use this information (HDD/CDD) to compare annual energy usage and to explain why heating/cooling costs will vary due to weather impacts or regional temperature differences (used in determining how much insulation is appropriate). For example in 2019 the Northeast had ~6000 heating degree days but Florida had ~ 2,500 heating degree days. Have a look at the regional map is here.
Insulation

The house with more snow on the roof is more efficient and has a lower energy bill because there is less heat loss through the roof due to better insulation values!
Obviously, we can save energy if we capture it and don’t let the heat out (winter) or let the heat in (summer). We can achieve this with insulation. Our older houses often do not have the required insulation because when they were built energy was cheap, and so the economic incentive was not present (or, as we will see much later, the national energy security was not threatened—yet). Modern housing is required to have certain insulation levels to meet the building code. What these values are will vary by geographic region (related to HDD/CDD). We use R values to measure the insulating property of the material (the resistance of an area of material to heat flow over time). The units are:
h= hours, ft2 is the area, F is degrees Fahrenheit, and Btu (British thermal units) is energy. So, as that is a mouthful, we just report the R-value as the unit.
As this is the resistance to heat flow, the higher the R-value the better the insulating ability. We can increase the R-value by adding more (thickness) insulation or by changing the insulating material to a higher R-value. Of course, if this is a wise investment or not depends on the climate (Heating degree days), how well the house is already insulated, along with the cost of insulation and the cost of heating. So, it makes sense to add insulation when the energy cost is high and the insulation costs are cheap. When energy is cheap, the payback period is too long. That is why old houses were poorly insulated. Now, however, the era of cheap energy is over.

The map below shows the EPA insulation zones for houses across the country. Both cold and hot areas (those with high HDD AND CDD) are required to have higher levels of insulation (higher R-values).

The chart below shows the EPA recommended R values for houses in (Zone 2), where Penn State's main campus is located. The highest R-values are required for the attic. R-values differ based on the area and location in the house (interior and exterior walls for example).

Air infiltration
Air infiltrates in and out of your home through every hole, nook, and cranny. About one-third of this air infiltrates through openings in your ceilings, walls, and floors. This provides a means for heat to escape or enter the home. Again this will differ due to area, location, and materials used in construction.


Home Heating

Natural gas is popular because of the (normally) low cost and ease of use (no cleaning up ashes, or arranging storage and delivery, etc). Not all of the houses have access to natural gas pipelines, so they tend to use electricity, or older houses (especially in the northeast) might use a fuel oil furnace. Had this course been taught in 1917, the local area would have been heated with coal. You may have heard the expression of getting coal for Christmas if you had been naughty. Coal was so abundant around the house for home heating, it had little value as far as children are concerned. Before the 1800s, biomass would have been the fuel of choice for home heating.
Biomass Combustion
Burning wood is still used in many nations and was, of course, the method of choice for the early settlers and Indigenous Americans. I still use wood furnaces to supplement my home heating as it is cheaper than using electricity. Cleanup is a pain and I often get yelled at for dropping bark on the floor or spilling ashes but it is nice and romantic on those cold winter evenings! Burning wood works because solar energy is stored in the plant in the form of chemical energy and then released as thermal energy during the combustion process.
Biomass is going to again contribute more to our energy mix. See the next lecture for why. Hint: Renewable Portfolio Standards!
Below you will find two videos from the US Department of Energy. They both provide a nice overview of home heating.
The first one, Energy 101: Home Energy Assessment (3:30 min.) discussed what a home energy assessor looks for when evaluating a home for efficiency, including insulation and air infiltration as described above.
In any season a leaky (high air infiltration) home costs money. How do you stop it? It starts with a comprehensive home energy checkup. That’s a series of tests and inspections to find out where your house could be more efficient. The end goal is to save energy, save money, and make your house more comfortable. Installing energy-efficient lighting and appliances will help. So will creating a sealed barrier around your house hence minimizing the leaks. Upgrading your home to save energy can put anywhere from 5 to 30% of your energy bill. To get a thorough home energy checkup, you’ll need some help from a professional. Look for a home energy technician, called an auditor, in your area. Now, in this cold-weather evaluation, the auditor starts on the outside, looking for problems around walls, joints and under the eaves. If there’s not a tight fit, you’re losing energy and money. Next the technician might head up to your attic to check for leaks in the top of your home barrier. That trap door could be a culprit, letting cold air pass into the house. A big part of the checkup is determining how well the insulation insulates. Insulation should be correctly installed in between all areas of the house frame. That means it needs to be evenly applied and not just jammed in spaces. And of course, if the insulation has fallen down, it’s not working. Your energy auditor will inspect the holes where electrical lines pass through. If they’re not sealed, they’re leaking. Then it’s down to the basement. Your furnace and water heater could be wasting energy. The auditor will check to see how energy efficient the furnace is. Furnaces generally lose efficiency as they get older, and it could cost you more to keep yours running than to replace it with a new one. Maybe all you need is a new filter. Some people haven’t changed their filter for months, even years. That gunk clogging the filter means your furnace has to work harder to heat your home. If the water heater is several years old, it may not be efficient, and if it isn’t insulated, it’s also losing energy. Now it’s on to the ductwork. The technician will inspect connections to make sure they make a tight fit. They have to be sealed to keep the warm air going where it’s supposed to go. If the screwdriver can go in the hole, it means one thing for sure: Money is going out. Now for the blower door test. The energy auditor will close all the windows and doors and anything else that let outside air in. This special fan will depressurize the home. The idea is to suck air out of the house, allowing outside air to rush into the home through all those openings you didn’t know about. OK, so with the windows and doors closed and the fan running, leaks are easy to spot with an infrared camera. In winter the auditor will scan the interior of the home looking for cold air rushing in. Here the darker the color, the worse it is. These black spots mean one big air leak. It’s an eye-opening experience. For this house, the recessed lighting fixtures are big problems. The auditor will also take a look at the kind of light bulbs in those fixtures. If they’re incandescents, they’re using a lot of energy. Warm compact fluorescents are an energy-saving alternative. So the home energy assessment reveals ways that energy escapes your home, costing you money. The good news is you’ll have a comprehensive home energy report showing which efficiency upgrades are right for you and where to stop those pesky leaks.
Now watch the 2:43 minute video about daylighting.
Windows do more than provide a great view (or not). When we maximize the use of windows to reduce lighting and heating needs It’s called daylighting. Daylighting combines lots of things – everything from the type of window, window placement. and interior design – to control how sunlight comes in. They all work to maximize benefits from natural sunlight. (Music.) Check this out. Windows that face south are best in the U.S. They let in the most light in the winter months, but little direct sun during the summer, keeping the inside cooler. North-facing windows are also good for daylighting. They let in even natural light with little glare and little summer heat. Windows that face east and west don’t work nearly as well for daylighting. They do provide lots of light in the morning and afternoon, but it often comes with lots of glare and excess heat during the summer months. (Music.) Have a look at this energy-efficient office building. The windows team up with skylights to provide most of the light you need. Notice the light color of the ceiling. It reflects and enhances the daylight so that it fills the room. And what about all the overhead lights? Most of the time, you don’t need them. To account for glare, this office building placed hoods outside around the windows. The hoods also cut down on summer heat, keeping the office cooler and more comfortable. On the inside, louvers or tinting reduce glare and also direct light to reflective surfaces inside, allowing plenty of natural light to come into work areas. One big help to daylighting is the window technologies available today. Windows are now way more energy efficient. They insulate while still letting the light you want in. And have a look at this. It’s an electrochromic window. This special window changes with the brightness of the sunlight outside. As the sun tracks across the sky, it darkens to keep excess heat out. It’s like giant polarized sunglasses. Daylighting can have a positive effect. Studies have shown that with good daylighting at the office, productivity goes up and absenteeism goes down, and that’s good for the bottom line. Natural lighting and heating means you use less electricity and lower your utility bill. And the more natural lighting, the more money you can save.