What is a passive home? 20, 21
Before we define what a passive home is, let’s make sure we have some building basics covered. We talk a LOT about the “building envelope.” The envelope refers to all of the parts of the home that keep the outside out and the inside in. These are your roof, walls and floor including all the bits and pieces inside like framing and insulation. We will mention thermal bridging below. We’ve provided references for most of the technical topics we discuss, but a quick definition for a thermal bridge is a construction component that conducts heat. In the case of a CruxHome, the arched trusses act as thermal bridges.
In a nutshell, a passive home is designed to use the least amount of energy possible. The primary means of accomplishing this is to reduce the amount of energy transferred between the inside and the outside of the home. There are various standards used to describe what a passive home is, but passive homes adhere to several basic principles:
Each passive home standard defines a maximum amount of energy consumption per square foot for heating and cooling. The numbers change depending on which standard you use and some standards are climate specific.20 The goal is to make the amount of energy used for heating and cooling as low as possible. This is achieved by making an awesome building envelope22 with LOTS of insulation,23 by making sure it’s tight (does not leak air), by installing excellent windows and doors, etc.*** Each standard defines a limit to how much air the building is allowed to leak,24 again lower is better.
***One of the core principles of passive home construction is to minimize thermal bridging.25 A CruxHome compromises on this point to achieve significantly reduced construction cost and building time. We compensate for this by incorporating additional insulation into the building envelope.26
Each passive home standard defines a maximum amount of total energy used for all purposes. Again the numbers change depending on which standard you use. Total energy includes heating, cooling, hot water and all electrical consumption. This factor incorporates home design as well as occupant behavior, but chances are if you want to live in a passive home, you probably like to turn the lights off when you leave the room!
Testing! If you want to call a home passive, you have to prove it. CruxHomes is owned by a Certified Building Commissioning Professional,2 so we are passionate about testing and proving our results. This testing includes an an air-tightness test (blower door test)27 and full commissioning3 of the home systems with verification of actual energy use of components under operating conditions. We will test every CruxHome we build to verify and document that it performs as it should.
How do you heat and cool a CruxHome ?
You can’t just stick a furnace in a CruxHome and call it a passive home. For a home to be truly passive, we need to do things a bit differently and take heating and cooling to the next level.
Before we dive into the nitty gritty, let’s make sure we have some HVAC (heating, ventilation and air conditioning) basics at our disposal. Right off the bat we have ventilation, which is the fresh outside air that is brought into the building. While we’re on the subject, a ventilator is what supplies that fresh air. Exhaust air refers to the air that you remove from a building (such as with a bathroom fan). A heat exchanger is a piece of equipment that moves heat energy from one place to another. In our discussion we are moving heat between inside air and outside air. An “air handler” is equipment that heats and cools air (the thing on the other end of your thermostat). The ventilation requirement is the amount of fresh air a building needs to maintain indoor air quality.
The majority of heating and cooling in a CruxHome is done with an ERV 28 (Energy Recovery Ventilator). An ERV uses exhaust air to heat fresh incoming air in the winter and cool fresh incoming air in the summer. ERVs are super efficient air-to-air heat exchangers (rotary air-to-air enthalpy wheels 29) that do most of the work for the air handler. In most typical homes, and non-passive buildings in general, the amount of air supplied to the building is dictated by how much heating and cooling the building needs. In a CruxHome, because there is so little energy transferred between indoors and outdoors, the amount of air delivered is dictated by ventilation requirements. In typical buildings, ventilation requirements are normally a small fraction of the air needed for heating and cooling.
The bottom line is, CruxHomes need a lot less heating and cooling and therefore a lot less air which is how they save so much energy!
You may be wondering, “Am I still going to have a thermostat?” The answer to that question is yes. To make sure you have complete control of your CruxHome, every home will also have a super efficient air handler for the days where you need a little extra oomf! When you’re entertaining or just looking for some extra comfort, you’ll be able to walk over to your thermostat and make it happen.
Building a passive home with typical building techniques is expensive. The price point for this type of passive home is approximately $300.00 per square foot. To continue using the example here on CruxHomes.com, you would pay $792,000.00 (plus land and interest, etc,) for a new 2,640 square foot passive home constructed with typical building techniques. With CruxHomes you will be paying approximately $166,900.00 for the same square footage. You can secure a brand new, green home with all of the added ecological cost saving technology built in, for $625,000.00 less. Why pay more than you have to?
Most of us live in communities where all occupied structures have to abide by building codes.30 Although they aren’t perfect, building codes31 are a form of protection for the public good. They are intended to ensure that all types of buildings operate within acceptable limits and are safe to use. However, some building codes hamper innovation. At CruxHomes one of our primary goals is to make passive home construction mainstream. Just like any new building technology, we are working to become certified32 as code compliant including the evaluations and structural tests to make that happen. But we have a huge advantage over other new technologies because CruxHomes has already been proven in Europe!
Passive homes built with typical building techniques are expensive, but they (more than) satisfy building codes. The core of our mission at CruxHomes is to Make Sustainable Homes Attainable. We believe passive homes should be within reach of anyone who wants to own a home. We need your help to make that future a reality. Please contact us for information on how you can help!”