How to design for thermal comfort in a home

Have you ever noticed that at times you can feel cold in your home even though the air temperature is exactly where you like to keep it? That's because, contrary to what most of us think, air temperature is not the main factor that determines human comfort in a building.

为了说明一点，让我们从户外开始。当室外温度达到20°C时，我可能会感到舒适，也可能会非常不舒服，这取决于很多其他因素——我是在阳光下还是在阴凉处?有风还是风平浪静?相对湿度是多少?我是站着，还是坐在暖和的东西上，或者是冷的东西上?

The outdoor temperature may read as the standard room temperature of 20-21°C outside, but if it's cloudy, windy and humid, I'll want a jacket. Conversely, if you give me a wind-sheltered spot in the sun on a 12°C day in March, I'll be down to a T-shirt in no time to burn my pale Canadian arms. Air temperature alone does not define human comfort; in fact, it is remarkably inaccurate as a measure of comfort given the credit we give it.

According to Engineer Robert Bean of the educational resource websiteHealthy Heating,“人体和空间之间的显热传递主要是辐射传递，而不是基于空气的。ASHRAE手册、医学期刊和室内环境工效学期刊都非常明确地指出，在正常活动水平下，人体与环境之间大约60%的热量传递实际上是辐射的。”

The average adult radiates about 150 W of energy, but when in a room at normal uniform temperature we get back about 50 W of energy, resulting in a net loss of about 100 W. The net loss you experience will vary depending on the thermal performance of the home.If you have cold walls and windows, heat radiating from your body will help warm them at the expense of your own personal comfort. If the temperatures of the surfaces in your home are warmer, you will feel more comfortable regardless of what your thermostat says.

Other environmental factors beyond just the average air temperature and heat radiating to and from the surrounding surfaces of your home will further muddy the waters defining comfort; this includes air speed (think indoor 'wind chill' factor), relative humidity in the enclosed space, stratification (the difference in temperature between your feet and your head) and air convection (air movement caused by temperature differences).

All of that and even a few other factors affect personal comfort, including your metabolic rate and how much clothing you are wearing.

How building design affects comfort:

Air temperature does affect human comfort; it is part of your thermal experience, but its predominant role is to warm or cool the surfaces of your home. Windows represent the coldest exterior surface of the inside of a home, that's why heat sources are usually placed below them to in effect 'wash' them with heat. That stops the convection engine and helps bring their surface temperature up closer to that of our bodies, and as a result, less heat is transferred between us and our environment, and so we feel more comfortable.

让我们回到外面一秒钟——这次是在一个寒冷的夜晚，在篝火旁。你可能会非常温暖，甚至热得不舒服，直到有人走到你面前，这时你会立即感到寒冷。这与你周围空气的温度无关，而是你的身体吸收了火散发的热量。你对家里冷热表面的体验是一样的，只是不那么明显，因为温度不是那么极端。但是在一个非常冷的夜晚，你肯定会注意到双层玻璃和三层玻璃之间的区别。

Despite the monetary investment we make to buy a home and the amount of time we spend in it, true thermal comfort isn't even on the radar of most new homes being designed and built. The walls just meet the minimum requirements of building codes, windows are usually just double-pane, and a forced-air system or electric radiators are expected to deliver comfort based on the readings of a thermometer that only considers a fraction of the variables at play.

The good news is that the characteristics of an energy-efficient and durable house are much the same as those of a truly comfortable house - high R-value building envelope, no thermal bridging, sealed against air leaks, triple-paned windows, humidity control andproperly designed heating, cooling and ventilation equipment, to name a few.

Thermal comfort = efficiency and durability:

• The less heat that is lost through the building enclosure, the warmer it will be, and less heat will be lost from your body to the walls and windows.
• As warm, humid indoor air comes in contact with cold windows in winter, it cools, the moisture within it condenses on the window, and the cooler, denser air falls, creating air movement and the sensation of a draft. The interior surface oftriple-pane windows are warmer than double-pane windows resulting in a less draft(if any), and reduced radiation loss from your body, so they are more comfortable to be near. Being warmer also means there is less risk of condensation and moisture damage to window frames and wall assemblies.
• Air leakage causes uncomfortable drafts，但它也会让水分穿过墙壁，在墙壁内寒冷的表面凝结。密封的房屋更热舒适，更耐用，操作成本更低。
• Floors are the contact point between us and our house, so additional body heat is lost as our feet conduct heat to a cold floor. To compensate for cold feet, people will often jack the thermostat up from the seemingly 'uncomfortable' room temperature of 20-21°C. Cold floors in an otherwise warm house are a result of insufficient insulation; that means a greater rate of heat loss and higher heating costs. There is also the matter of conductivity - a wood floor and a concrete floor at the same temperature would feel very different since concrete conducts heat much better, making it seem either warmer or colder than a wood floor of the same temperature.
• It is important to note that including in-floor heat is not a reason to insulate less - in fact, you should insulate more. You may still be sufficiently comfortable, but a greater temperature differential between the floor and the ground below will increase the rate of heat loss, and your heating bills.

Measuring and designing a home for comfort:

A more accurate reading than air temperature for maintaining a comfortable indoor environment would be the MRT (mean radiant temperature), which is a measure expressing the influence of surface temperatures on occupant comfort.

An even more functional measure of thermal comfort in a building would be the operative temperature, which considers air temperature, mean radiant temperature and air speed. I've never seen such a device in a home but apparently they are available commercially.

The lack of true thermal comfort in newly-built homes can be easily traced to one key problem - the people we put in charge of design. Even nobly-intended general contractors regularly talk clients into the less-than-ideal building envelopes that they are most familiar with, or less nobly - feel they will profit the most from. That may also include well-intentioned 'money saving' recommendations to downgrade from triple-pane windows to just double-pane windows, and reducing basement slab insulation to as little as they can get away with.

在加热、冷却和通风方面，系统的设计和尺寸通常留给安装人员，而不是在这方面受过培训的工程师。安装人员接受的培训并不是如何设计一个全面的家庭舒适传递系统，他们只接受了如何安装的培训。不要让你的工程师安装系统，也不要让你的安装工程师安装系统。

Leaving the heating system design in the hands of installers produces one pretty consistent result - systems that are oversized for their space. And this ensures one very important thing (at least for installation contractors) - they won't receive a call from angry clients complaining of a lack of heat. Homeowners will instead get powerful blasts of hot and cold air from systems that are unable to run at their most efficient rate, because they are conditioning a space much smaller than what they were designed for.

Again, this may be well-intentioned, but it is not in your best interest. Over-sized heating equipment is more expensive to purchase, and it starts and stops more frequently rather than running for longer periods of time at its optimal rate. That brings added system wear, less comfort and higher operating costs. This would be akin to the added gas used and brake wear when racing from red light to red light in a car instead of driving at an even speed and getting all the green lights.

这个学科的工程师会根据你的特定气候、建筑围护结构、气密性来计算你的热负荷，然后设计一个系统来满足这些需求。

Radiant heating:

There is seemingly endless debate in green-building circles as tothe comfort benefits of radiant heat, specifically floors. Walls and ceilings can equally be heated and cooled, it is just much less common. Studies seem to show that there isn't a lot of energy savings reported in homes with heated floors, despite the fact that, in theory, there should be.

With heated floors, the air temperature is higher at ground level (where people are) rather than heat collecting around the ceiling above our heads (where people aren't), which is what happens with most heating systems where the primary intention is to heat the air.

采用地板供暖的房屋缺乏节能报告，可能是人们把恒温器留在原来的地方，只是享受温暖的地板和平衡的热量带来的更大舒适度。如果他们不节省能源和金钱，那么至少他们可能会更快乐，这也是一件好事。如果建筑设计优先考虑居住者的热舒适，我们很可能会看到更多的辐射供暖，当然也会看到更好的建筑围护结构。

If you are custom building a new home, your best chance for a comfortable and efficient final product would come by employing a designer who leans towards high-performance (experience withPassive House实践是一种奖励)，并选择一个不会与你的设计师发生冲突的总承包商，并试图说服你采用他们自己喜欢的实践。让设计师设计，让建设者建造。

So that's how to design a home for human comfort, to learn how to carry that out, read here aboutthe importance of balancing insulation,avoiding thermal bridges, andhow much insulation a basement needs. TheEcohome Green Building Guide Pageshave all the information you need to build healthy,energy-efficient and resilient homes.