It’s important for homeowners to understand the difference between active and passive systems. One can save you a huge amount of money on the other!
Active vs. Passive Systems
Active systems like mechanical (heating and cooling), plumbing and electrical systems have a first cost (purchase + installation) and ongoing costs. They have moving parts that need to be maintained and they require energy to operate.
In contrast, passive systems are those systems like air sealing and insulation that have a first cost with no additional costs. Once passive systems are installed, they function without any additional input or maintenance.
The Cost of Active Systems
Home owners constantly invest in active building systems. Whether those active systems are mechanical (heating and cooling), plumbing or electrical – they have four costs:
1. A first cost: purchase + installation
2. An operating cost: the cost of fuel, electricity or water
3. A maintenance cost: repair or replacement of parts that no longer work properly; and
4. A replacement cost: the entire system is too old to function (safely), the (ongoing) maintenance cost will exceed the cost of replacement or the system is too inefficient to make the cost of fuel, electricity or water cost effective.
You could also argue there’s a fifth cost to every active system: the safe disconnection and removal of that system. For example, systems that use natural gas must be properly disconnected and air conditioners with regulated refrigerants must be properly drained before being removed.
The Beauty of Passive Systems
Passive systems are a game changer when it comes to saving money because they only have a first cost. They can help protect you against rising energy costs.
Active systems like your air conditioner use energy to cool your home. Passive systems like insulation help keep that energy from escaping. If your home is efficient – it doesn’t quickly lose energy through its exterior (floor, walls and ceiling) – your air conditioner and furnace don’t need to put as much energy into the home to keep it comfortable.
That means your passive systems have reduced the demand on your active systems so smaller active systems can be designed, installed, operated and maintained. Thus, well-designed and properly installed passive systems like air sealing and insulation can reduce the size and cost of your active systems. Reducing your energy consumption through passive systems helps protect you from rising costs: higher seasonal energy rates + higher natural gas and electricity prices.
Design as a Passive System
It’s possible to invest too much in passive systems. For example, there are limits to the amount of insulation that it makes sense to install. In the southeastern United States (Climate Zones 2, 3 & 4 of the International Energy Conservation Code), that limit is about R-20 in the walls. If you install much more than that amount of insulation, the return can quickly diminish as the cost rises.
It’s important to carefully invest your budget in the right places. Though passive systems like insulation may seem simple, the success of that insulation depends on a design that calls for the right types of insulation in the right places of the home’s exterior (floor, walls and ceiling). The design of the home needs to account for its systems, both active and passive, rather than treating them as an afterthought or following the minimum requirements of the building codes.
Investing in passive systems like air sealing and insulation isn’t just about energy efficiency. This is particularly true for existing homes that were built before energy efficiency was much of a concern. Those homes may not just have efficiency issues, they may also have health and comfort issues – which are much more difficult to quantify in terms of cost.
An energy retrofit of an existing home often involves:
1. Sealing air leaks,
2. Adding insulation where needed; and
3. Upgrading to more efficient lights, appliances and fixtures where it makes sense.
Those first two items can be very challenging when it’s difficult to gain access to the places where that work needs to take place. For example, the work to seal and insulate exterior walls can involve opening those walls from the inside or removing exterior cladding to gain access from the outside.
It’s easy to lose perspective if you only look at the cost of an energy retrofit on an existing home compared to the return on investment in energy savings. The work may cost more than the anticipated energy savings over the life of the home. That’s why it’s important to also consider the health and comfort improvements that the proposed work will provide.
For example, if you have air leaks between your crawlspace and your living area, you’re probably introducing humid air with dust and allergens into your home through those air leaks. Sealing those leaks will likely improve your health + comfort and you’ll no longer be paying to condition the air and humidity that’s leaking into your home.
In recent years, the construction industry has gained some wonderful diagnostic tools for verifying conditions in homes, both old and new. We can use infrared imaging to see heat flow – a great way to spot areas with missing insulation without opening walls. We can pressurize homes and air conditioning systems to find (and seal) air leaks. We can also use sophisticated energy modeling software to estimate whether investments in passive and active systems will create the desired outcome.
It’s exciting to be working in a time when industry professionals use those tools to take much of the guess work out of improvements intended to address health, comfort and efficiency. Home owners can also have real-time energy monitoring systems installed to help them make better decisions about their behavior. You get to compete against yourself as you might with the average gas mileage number constantly calculated and displayed in new cars – better information can result in better decisions.
If you’re tolerating health and comfort issues or high utility bills, please give some thought to hiring a professional with the knowledge and equipment to find the best design solution for your budget before you hire a contractor. You can look forward to learning a great deal about your home and using some great new tools during the design process.
As always, if you’ve got a comment or question, please share it below. Thanks!
Image by dagnyg used under creative commons license.