Thermal Comfort in the Home
Thermal Comfort in the Home
What makes you feel warm? What makes you feel cool? If you’re like most North Americans, when you think of these things in the context of your home, you’ll think of that little box on the wall: the thermostat. We’ve been trained by years of forced-air heating systems and baseboard heaters to believe that air temperature equates to feeling comfortable. But that’s not necessarily true.
“Think about being outdoors on a cold sunny day,” says Goran Ostojic of Cobalt Engineering. “It’s 10 degrees Celsius, yet you can sit in a nice sunny spot protected from the wind and enjoy your coffee. Now imagine a cloud blocks the sun. Suddenly you become cold because the air temperature is actually only 10 degrees. It was the radiant energy from the sun that was keeping you warm.”
Radiation is how energy reaches us from the sun.
Feeling comfortable indoors comes from a variety of elements (see diagram) – many of which, such as humidity and air movement (drafts) are addressed in building design. Air temperature does play a role – but we’ve given it too much focus in the way we design our homes.
Feeling comfortable indoors comes from a variety of elements – many of which such as humidity and air movement (drafts) are addressed in building design.
“Air is a very bad heat transfer mechanism – it’s actually an excellent insulator,” says Peter MacLellan of Olympic International. “That’s why forced air systems use so much more energy – they’re designed to maintain a particular air temperature. With radiant heat, we can have people be comfortable without concentrating on changing the temperature of the air. And it turns out to be much more efficient because you don’t have to pump all that air around all the time.
“With a radiant system you have no thermostat giving an air temperature readout. It doesn’t have a direct correlation to comfort.”
How Radiant Heat Works
Snowflakes falling in the air while you sit comfortably under an outdoor restaurant radiator. Shivering uncomfortably next to the cold glass of an office window despite a normal air temperature. Feeling relief near a cool concrete wall on a hot sunny day. All these are examples of radiant energy transferring heat from one body to another.
Feeling comfortable indoors comes from a variety of elements – many of which such as humidity and air movement (drafts) are addressed in building design.
“Heat transfers in three modes only: convection [fluid movement that carries heat, such as forced air heating], conduction [heat transferring without movement, such as a mug growing warm from holding coffee], and radiation,” says Goran Ostojic of Cobalt. “Radiation is how energy reaches us from the sun. It crosses a vast distance of universe with no air and warms the earth. A radiant exchange occurs between two objects or elements with mass that have different temperatures. The air is completely insignificant.” So radiant heating and cooling systems act directly on your body as you absorb or release heat energy to the other objects around you. Understanding the power of radiant energy – particularly what comes from the sun – is the first step to recognizing the importance of integrated, passive design in creating comfortable, energy-efficient places to live.
The psychrometric chart is a graph of the physical properties of moist air at a constant pressure (often equated to an elevation relative to sea level); it is a useful tool for engineers concerned with thermal comfort and passive design. The chart graphically expresses how various properties (dry bulb temperature, wet bulb temperature, dew point and relative humidity) relate to each other.
Passive Design: “Building a Better Building”
Don’t fight Mother Nature. And work as a team. That’s the advice on how to achieve high-performance, energy-efficient buildings. “First, take advantage of the environment through passive design – a proactive approach to achieving comfort,” says Albert Bicol, one of Cobalt’s engineers on the Olympic Village project. “Then use mechanical systems – which are reactive – to supplement as needed.” This approach uses less energy because it’s not battling the glaring heat of summer (thanks to solar shading) or losing energy to the chill of winter (due to high-value insulation).
It makes sense, but it’s not how most North American buildings are designed. “Buildings are becoming a commodity service, where various building design professionals operate in their independent silos,” comments Cobalt engineer Vlad Mikler. “We’ve had very low cost energy, so we’re not motivated to get as much as we can out of passive design, because it requires multi-disciplinary coordination to a much higher degree.”
This micro climate diagram highlights the key challenges and opportunities, from a design standpoint, for each façade orientation.
Mike Mahannah, President of Olympic International, agrees. “There was no way this [radiant heating] technology could have been applied if the architects and engineers didn’t work together – the needs for heating and cooling would be too intense. You have to build a better building. It takes cooperation to make this all work.”
“The results appear quite extraordinary,” says Mikler. “But in fact it’s just the proper way of designing buildings. There’s nothing magical about it.”
Energy Modelling
To determine how a building design will perform in terms of comfort and energy usage, engineers use energy modelling. A three-dimensional computer model of the building is established, and then information about a wide variety of elements is assembled: the insulation value of the walls; the interior conditions to be maintained (i.e. ideal temperature and humidity); the schedule of occupancy; and the planned mechanical systems. Engineers then add the weather.
“For Vancouver we a have database of standardized weather data for every single hour in an entire typical year,” says Vlad Mikler. “The simulation allows us to calculate the peak conditions for heating and cooling, as well as the building’s aggregate energy consumption over the whole year.”
It makes sense, but it’s not how most North American buildings are designed. Buildings are becoming a commodity service.
Mikler says the simulation is run twice – once for the building being designed and once for a hypothetical building with the same dimensions and location, designed to meet only minimum code standards. The hypothetical building establishes a benchmark against which the planned building can be compared. Modelling for the Olympic Village buildings predicts they will be 30% to 70% more energy efficient than their reference cases.
Cobalt’s engineers say they are lobbying against the current system of energy modelling, since it provides a comparison only between a building and its own minimum code reference case (which can be somewhat subjective). A better system is one now being adopted in Europe, which assesses energy intensity – the amount of energy used per square metre. This system provides a standardized baseline, which allows different buildings to be compared and supports policy that regulates the total energy a building may consume. (See Global Voices).
Water: the Key to Moving Energy
This schematic shows the heating and cooling systems within the Olympic Village buildings, from the NEU supply through to ceiling installed capillary mats within units. During cooling, unwanted heat energy is collected by the system and used to pre-heat domestic hot water. Any remaining heat is vented into building
parkade ventilation systems. A key element to efficiency is the system’s hydronic (water-based) technology. Water is 3,000 times more efficient at carrying energy than air. Therefore, the power used for pumping heated water – per unit of heat energy transferred – is approximately one-tenth what is required to transfer the same
heat using a forced air system.
In-Suite Heating + Cooling
Capillary Mats
With passive design planned and hydronic radiant energy the most efficient space-heating option, the Olympic Village’s design team had to select a specific system for thermal comfort in the Village’s many homes. They chose a radiant “capillary mat” system invented by Donald Herbst in Germany in 1981 and installed extensively in commercial and residential buildings in Berlin. The inventor likens the system to the capillary veins in
a leaf – or those in a human body, which maintain body temperature at a constant 37 degrees. Mats made of multiple thin-gauge tubes circulate water (warm or cool) across an extensive surface area, exchanging energy with any nearby mass.
Radiant energy transfers heat from a mass with higher temperature to one with lower temperature, in the same way we are warmed by the sun. When the radiant system is switched to cooling, it draws heat from objects – including bodies – that are warmer than the water, giving a cooling effect.
“Radiant heat always moves in one direction only – always from the warmer element to the colder element,” says Goran Ostojic of Cobalt. “During the winter we heat the ceiling to a slightly higher temperature than we want to achieve in the space. The ceiling radiates to all the solid objects in the room, whether it’s a human body or the furniture or your pot of coffee, and the opposite occurs in the summer, when we cool the ceiling to a temperature below what we want to achieve in the space. Then all the solid objects are losing heat towards it, so a human body is losing heat.” The system is governed by a simple control where the resident can shift the
system between “heating” and “cooling” and adjust the intensity depending on their comfort level. (Non-market housing does not include a cooling mode.) The system has no blowing air, so maintenance is reduced, and there is no noise from fans, nor movement of dust or allergens. And since the system doesn’t produce hot air, a resident can opt for warming while also having a window open for fresh air – and not “let all the heat out” of their space or waste significant energy.
Capillary mat heating is a “low intensity” system. Due to the extensive area covered by the mats, the temperature differential between the circulating water and the bodies it interacts with does not need to be extreme (i.e. water heated to 38-41 degrees Celsius). This contributes to the system’s energy efficiency.
Energy Transfer Centre
The operating systems for each suite includes: hot/cold circulating water; a circulation pump; an expansion tank; control valves connected to the comfort control (room by room); and monitor wiring for usage reporting. These components are located in a panel, called the Energy Transfer Centre, which is mounted in storage rooms or closets in the suites. The system also includes a sensor to determine whether unacceptable condensation has developed (during cooling mode), which then shuts off cooling until humidity subsides.
In-Suite Radiant Heating and Cooling System
Lighting + Incentives
Lighting Design
Lighting design at the Olympic Village had to balance a mandate for energy efficiency with the need to create inviting, enjoyable spaces. Efficiency measures included motion sensors that dim corridor lighting when no one is present, and multiple zone design, so that residents can choose to turn off light in areas they’re not using. But the company that handled lighting design for the majority of the Village’s buildings opted against sustainability’s poster child: the compact fluorescent lamp (CFL). “They’re poor sources of light, in terms of quality,” says Steve Nemetz, of Nemetz (S/A) and Associates, the company that handled electrical engineering in the Village. “It’s flat light, with poor colour rendering, and some people react badly to it.”
“We aimed for energy efficiency and colour temperature, not too bright or too dim. It’s about quality of light, not quantity.”
Steve Nemetz
Instead, the company choose low-wattage MR16s, a halogen lamp. (In BC Housing properties, some CFLs were mandated.) “CFLs always require a ballast [a device that limits the amount of current the lamp draws],” says Nemetz. “A 13 watt CFL with a ballast uses about 15-16 watts of power, and dimmable ballasts are expensive. Instead, you can use a long-life 20 watt MR16 and get the same amount of light, but with better colour rendering, much better atmosphere and similar longevity.”
Another feature of sustainable lighting design (worth a LEED credit) is to minimize light trespass – the unwanted entry of exterior light from one home into the next. After that, it was time to set the mood. “You’ll see many architectural features that are highlighted,” says Daisy Chan, lighting designer with Nemetz. “We’ve worked to ensure there’s good feature lighting, in lobbies for example. Light can make or break a space. If it’s lit improperly, you’ll have a different impression.” “At the end of the day we’re very happy with the lighting and the distribution,” says Nemetz. “We’ll be able to be proud of it. It’s quite amazing.”
Pendants used in areas such as lobby and amenity with compact fluorescents.
Power Smart New Construction Program
The Olympic Village is the largest project ever to participate in BC Hydro’s Power Smart New Construction Program. The program funded an energy study to identify energy conservation measures and estimate potential savings. It found that the Village’s conservation strategies – ranging from radiant heating to Energy Star-rated appliances – will save enough electricity to power 1,040 homes per year. Based on the energy saved, the program provided capital incentives to offset part of the upfront costs of the efficiency measures.
“At BC Hydro, our motto is to consider generations to come,” says George Crowhurst, BC Hydro’s key account manager for the Olympic Village. “This project will show our children what we did, that this was the innovative way to go at this time, and it gives a baseline for going further. Innovation for saving energy will only grow.”
Educating the Market
One challenge faced by those involved in energy design was dealing with current perceptions about what the market demands in a new residential suite. While the superior performance of radiant heating sounds luxurious, for example, marketers say buyers demand floor-to-ceiling glazing (windows) to maximize views. You can’t have both – windows lose too much heat. “People may think they want huge windows, but not when they realize that there’s a trade-off – these impact on comfort,” says Vlad Mikler. “We tend to focus on what we marketed in the past. Now we have to educate buyers rather than just promoting what we’ve already done for 20 years. We can turn comfort and efficiency into a marketing advantage, but few [marketers] are doing it.”