The House as a System

Rate this post

Before we build a home (or hire a contractor to build it for us), we need to understand how the house works as a complete system. It is much easier to build a green home once we become familiar with some key principals such as how heat and cold gets transferred, and the reasons why moisture and air move throughout our homes. It is even more important to understand how a house works as a system; this saves both on energy losses through air leaks, and added moisture.

The transfer of heat

To understand heat flow it is best to look at the laws of thermodynamics (the study of energy) that is, thermo (heat) and dynamics (movement).  Once we understand these principals, we come to understand that science plays a big role in building a home, as well as the more commonly thought-of nails, wood and hammers.

There are two laws of thermodynamics:

1) The first law of thermodynamics states that energy can be changed from one form to another, however it cannot be destroyed. Energy exists in many forms including solar, chemical and electrical. In fact, the total amount of energy available stays the same – it just changes to different forms.

2) The second law says that in all energy exchanges, the potential energy of that state will always be less than the initial state. In other words, whenever energy is converted it gets downgraded in the process. This process is what is referred to as entropy.

You may be thinking right about now, what do these laws have to do with me building a house? It’s just bricks and mortar. These laws of science actually play a rather large role because when building a home you want to make it as efficient as possible.

A house that is electrically heated is nowhere near as efficient as a home which takes advantage of passive solar design features. Homes that utilize electricity typically come from fossil fuels such as coal. Coal as an energy source requires much energy to change from one form to another. A big chunk of this energy ends up getting ‘lost in transit’ and therefore by the time the usable power is delivered to a house its energy potential is very low. Sometimes by the time useful energy reaches a house its net energy is only 15 per cent of its original. That is, electricity has lost 85 per cent of the potential energy coal used to make it through transportation, refinement, generation, transmission, and transformation by the time it reaches the end user. I don’t know about you, but in a world where the supply of fossil fuels is running out by the day, finding an alternative is very much a reality for me.

Instead of using fossil fuels i.e. non renewable energy, have you ever thought about passive solar design? Solar design uses the power of the sun to create energy and in the process reduces the amount of energy a house will consume.  The sun as an energy resource is ever abundant and most areas in the world have enough sun energy to harness this energy. Even areas where the sun does not shine brightly every day, surprisingly there is still enough energy to power homes throughout that specific area.

Unlike with electricity conversion, solar conversion only uses one conversion process. That is, the sunlight shines through windows in your home and hits an object which is then radiated to human bodies giving us heat.

People find passive solar design a great way to reduce heating and cooling bills, and reduce wear and tear on heating and cooling equipment. These techniques are easy to apply when building new because you can control the placement of the home and were you put the windows (i.e. north facing, south facing etc). However, if you live in an existing home you can still take advantage of solar energy technologies. Some of these technologies include energy efficient windows, solar panels and rainwater catchment.

When we build a home and want to incorporate green elements, the process is easy once we have a clear understanding of entropy. We come to realize the role that well-designed windows play and the type of appliances we should use to make our homes run as smoothly as possible, using the least amount of fossil fuels.

How heat moves

The flow of heat is the flow from hot to cold, and is an important concept to understand. Heat is energy, and as long as there is a difference in temperature, heat will move.  Ever notice how when it is cold outside and you have the heater or fire on, you leave the outside door open even briefly the warm air sneaks out the house? Heat always moves from hot to cold and keeping this warm air inside the home is imperative to keep you feeling comfortable as well as saving you money on utility bills. This concept is important when building a home in order to truly comprehend how to heat and cool our homes, and how to control added air and moisture in our homes.

There are three ways that heat can be transmitted and energy movement is always a combination of three movements of energy: conduction, convection and radiation.

1) Conduction         

Heat conducts through solid substances in the conduction process. Conduction is usually measured in insulation terms. R-value is a measure of thermal conduction – the higher the number the greater the resistance to heat flow. This means that heat will move more slowly through the material. You will also find that anything that conducts electricity will have a low R-value. It is important to have good insulation in a home to limit the amount of heat loss. To do this we need to use low conducting materials.

2) Convection

Convection happens due to density differences between warmer and cooler parts of a fluid.

In simple terms, the hotter the fluid is the less dense it is. Hot air rises and this is why warm air remains in the upper levels of a home and the basement stays cold. Even using your morning coffee as an example: when you blow on your drink to cool it down, convective heat loss occurs between the drink and the air. It is important to understand convection because when not controlled, convection can result in a cold house and damp house.  It’s not only utility bills that will sky rocket if you have a cold damp house, but dampness which can lead to mold and mildew which can have catastrophic effects on your family’s health as well.

3) Radiation

Radiation occurs when heat passes from one object to another. For instance, the sun radiates heat and when you stand next to a cold object such as a window, your body radiates heat towards that object, and that is the reason you feel cold. Radiant floor heating is often a popular choice for consumers and is often said to be the most energy efficient and comfortable heating method on offer today. With a forced air furnace, hotspots are created only where the air blows and in high ceiling areas, however radiant heating provides an even temperature throughout the house.

Not only will radiant floor heating increase the comfort levels of a home, it will cut the heating bills of a house more than other traditional heating methods can do.

Controlling heat flow

It is important to build a house in order for you to remain comfortable and keep the cold air outside and the warm air in. You need to make sure that you build your home to respond to the environment around you. Once this is achieved, no matter where you are in the country, you can design your house so that you can control the flow of heat.

When looking at controlling heat flow, insulation is the key element that you need to consider. There are a number of options when it comes to insulation choices and most are available from a home center store or large hardware retailer. Before going to the store to purchase insulation it is best that you measure the areas to be insulated beforehand so that you purchase the right amount of material.

Depending on where you live, the amount and R-value of insulation you require differs. However, remember that the more insulation you have, the warmer and more comfortable your home will be.  The Department of Energy website which is regularly updated is a great resource for you to use and has a helpful insulation calculator www.ornl.gov/~roofs/zip/ziphome.html.

If your home was built before 1981 you will probably need to add insulation, and if you are currently remodeling your home there is an easy way to add insulation. When it comes to insulation people tend to know what `Pink Batts` are but most are unaware that there are other types of insulation as well.  You need to realize that no type of insulation is the same and each different type is used for a different purpose and has a different R-value.

Batts are the most common form of insulation available. They come in either fiberglass batts, non-fiberglass batts or wool and cotton batts, and are often described as ‘fluffy blankets of insulation’.  Batts are easy to install and sit easily in the space between the studs in a wall. As with all insulation choices there are tradeoffs in terms of performance, cost, and the amount of chemicals they contain. Avoid fiberglass batts if possible. However, if you do choose to go with fiber glass batts, choose formaldehyde free and make sure the installer knows what he/she is doing.  There are three choices with batt insulation: foil-faced, kraft-faced and non-faced. They all have their benefits and limitations. Talk to your local insulation professional about what choice is best for you.

Loose fill insulation is another popular insulation choice and as the name suggests, loose fill is made up of small pieces of insulation that is blown into place using a special piece of equipment. Fiberglass and cellulose are the main loose fill options available, they are both cost competitive; however cellulose is a better insulator. Cellulose has a R-value of 3.7 whereas fiberglass has an R-value rating of 2.8. Loose fill insulation is a popular choice in small and hard to reach places such as in the attic. If you choose to install loose fill insulation into the walls, it needs to be held in place with netting or held in place while the wall is being completed.

Spray-in Insulation is similar to loose fill insulation. It expands into a foam, filling every possible area even in hard to reach places. Spray-in Insulation has high R-values, creates a super insulated area and is great for sealing tiny gaps.  The one down side to spray-in insulation is that they are one of the most costly options and not an option you should consider if you are looking to save money. However, the one thing you need to keep in mind is that by spending up now, in the future you will be much better off and will be living in a warm and comfortable home.

Rigid foam is a stiff board and when applied to the outside of a framed wall is a great way to keep wall cavities dry and reduce the risk of mold. More expensive than batts and loose fill, rigid foam has more than double the R-value of batts and loose fill making it a great choice and especially effective where space is limited. If you are remodeling your home and you want to incorporate insulation in that process, you may want to consider rigid foam because it is easier to add insulation to the outside of a framed wall rather than removing a wall and adding insulation i.e. batts or loose foam, and replacing the wall again.

Air leakage

Air leaks can be responsible for approximately 25 per cent of the heat loss in a new home, and even more in older houses. Leaky Building Syndrome is an issue affecting homeowners worldwide. Air leaks are an important part of the equation, often causing mold and structural deterioration.

To determine whether your home is suffering from air leakage you can do a blower door test which must be performed by an energy auditor or a heating contractor. These tests shouldn’t cost you more than a few hundred dollars and are a great way to check if air leaking areas should be sealed.

Once you have all air leakage problems sorted out it is important to have good ventilation i.e. fresh air needs to be able to come into your home. Don’t ever think that you have tightened up your house too tight by sealing all potential air leaks, you haven’t.  Mechanical ventilation is the next step that you should take to control the flow of fresh air in your home. Not only does mechanical ventilation control the flow of fresh air in your home, it also helps define the correct pressurization of a house.

Leave a Reply

Your email address will not be published. Required fields are marked *

*