If you’ve been following Sunset Green Home, you know that the LEED for Homes green building program focuses on aspects of sustainability such as energy efficiency, water efficiency, sustainable site design and healthy indoor air quality. But did you know that following the LEED for Homes guidelines results in greater thermal comfort for a home’s occupants?
On average, Americans spend approximately 90% of their time indoors. So the LEED for Homes green building program offers strategies for achieving healthy indoor air quality – one aspect of which is occupant thermal comfort.
Thermal comfort, which refers to a person’s satisfaction with the temperature of his or her environment, is influenced by several factors, each of which I’ll address in turn:
- Air temperature
- Air velocity
- Relative humidity
- Radiant temperature
1. Air Temperature
LEED for Homes encourages projects to install multi-zone systems for heating and cooling, which allows occupants to tailor the temperature of a space to their own perceived level of comfort. In the Sunset Green Home project, we installed a four-ton five-zone Mitsubishi Hyper Heating inverter-driven heat pump system (sized using ACCA Manual J calculations…more about that later). Not only is the system extremely energy efficient, but with a variable speed compressor, it delivers an even rate of heating and cooling once its set points have been reached.
But air temperature isn’t controlled by mechanical heating and cooling alone. Sunset Green Home also implemented strategies to provide passive means of keeping the air temperature where we want it to be:
- High quality windows resist solar heat gain
- Automated solar shades made of high performance fabrics preserve the view but cut down on the amount of solar heat admitted into the house. Sunset Green Home's shades are tied into our Elan g! home automation system, which raises and lowers them automatically
- Insulation levels that exceed Code requirements and attention to air sealing result in a home that naturally stays cooler in the summer and warmer in the winter – without any draftiness
2. Air Velocity
Air movement reduces the temperature perceived by a room’s occupants. The LEED for Homes program rewards projects that install ENERGY STAR rated ceiling fans in each bedroom and in the living spaces.
But not all fans are created equal and occupant behavior can sometimes lead to INCREASED energy use rather than reduced energy use. According to a 2013 article published by Green Building Advisor, “The same way a breeze cools you off, a ceiling fan can make you feel cooler, but only if you are close enough to it to feel the air blowing on you. If you can’t feel it, it isn’t doing any good.” The article goes on to assert that another hazard with ceiling fans is that some have motors that create a great deal of heat – which runs counter to the desired cooling effect that most occupants hope to achieve.
Big Ass Fans has come up with a solution to address both of these potential ceiling fan drawbacks. The Big Ass Haiku model is the most energy efficient ENERGY STAR rated fan available – and an energy efficient motor generates less heat than a less efficient motor. And Big Ass Fans has developed SenseME technology, an advanced technology that “monitors the room’s temperature and humidity, adjusting fan speed when conditions change.”
"The typical home has more than three fans, but they’re no smarter or better looking than your great-grandma’s,” said Carey Smith, founder and Chief Big Ass of Big Ass Fans. “In the past couple of years, we’ve seen smart thermostats and smart light bulbs, yet you still have to pull a chain to start your ceiling fan. SenseME changes everything." According to Big Ass Fans, “SenseME knows when you enter or leave a room, turning Haiku on and off automatically.”
According to the US Department of Energy, “using a ceiling fan will allow you to raise the thermostat setting about 4 degrees without impacting your comfort.” Sunset Green Home elected to install Big Ass Haiku fans with SenseME technology in each bedroom, the living room and den, the screened porch, and in the pool cabana, which is not air conditioned. By installing Haiku ceiling fans throughout the home, we have been able to commission our air conditioning at set points that are several degrees above where they’d be if we didn’t have the fans. We’re cool and comfortable, and saving energy at the same time!
3. Relative Humidity
LEED for Homes requires a project to size its heating and cooling equipment to its actual thermal load using industry standard calculations developed and approved by ACCA, the Air Conditioning Contractors of America, a non-profit body that creates that standards for HVAC design and performance. The ACCA system sizing calculation (called a Manual J) ensures that a home’s heating and cooling equipment is not oversized. Why is this important? An oversized air conditioning system will reach its set point quickly and will then cycle off until the thermostat perceives that the temperature has moved beyond an acceptable deviation from the desired temperature, which in turn causes the equipment to start up again. This on/off cycle can lead to humidity problems inside a home.
Ideally, air conditioning equipment should run consistently; moisture is removed from the air as it passes across an air conditioner’s coils. But a system that experiences “short cycling” will doesn’t move enough air across the compressor’s coils to dehumidify it. Because it was sized using the ACCA Manual J calculation, Sunset Green Home’s Mitsubishi heating and cooling system’s properly sized variable speed compressor ensures that air is constantly moving across the coils. And the system can be operated in “Dry” mode, which keeps the coil temperature just below the dew point of the return air to remove unwanted moisture from the home.
4. Radiant Temperature
Radiant temperature refers to the heat emanating from surrounding surfaces. LEED for Homes addresses radiant temperature effects through credits aimed at reducing the “heat island effect” – which occurs when surfaces in and around a structure absorb heat from the sun, and then radiate that heat into the structure and into the air around it. By minimizing local heat island effects in warmer climates, a home’s air conditioning system won’t have to work as hard – or use as much energy – to cool the house. We can minimize heat island effects by using light-colored materials for roofs, decks, driveways and sidewalks, and by providing shading to hardscapes. Sunset Green Home installed a light colored permeable pebble driveway to reduce the heat island effect.
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You don’t have to seek LEED certification to make smart decisions that will deliver energy and cost efficient thermal comfort. When you are looking to install or upgrade your heating and cooling system, consider a multi-zone system to allow for individual occupant comfort, keep the air moving in occupied spaces to allow for more energy efficient temperature set points, and keep humidity at bay by not oversizing your system. You’ll be comfortable, your pocketbook will be happier, and you’ll be reducing your impact on the environment. This is a win-win-win for triple bottom line principles of economic, human and environmental impact.