Hundreds of Thousands of Years of Evolution
If we think of our biological heritage we evolved with the sun and fire. Both deliver light and heat in the form of infra –red radiation. In terms of our evolutionary make up it is probably fair to say we react well to a source of radiating heat, warm surfaces, cool air and probably a little air movement.
A Cool Head and Warm Feet
In addition we know that certain parts of our body are more susceptible to heat loss (or gain) than the rest. We know that a cool head (speaking strictly in thermal terms) aids concentration, while cold feet are particular uncomfortable and that in general we require a cool head and warm feet (and to a lesser extent hands) to be comfortable and function well.
All of these aspects and more need to be considered when deciding on the heating regime of the building and its occupants bearing in mind too that occupants needs change with the days the seasons with age and from person to person.
So what is a healthy system like?
Warm Surface Temperatures – radiant heat like heat from the sun
This is possibly the most important aspect of thermal comfort yet it hardly registers in discussions about heating. We gain and lose a significant percentage of our heat through radiation heat exchange. What we need are surfaces which are a few degrees warmer that the ambient air temperature.
The way to actively warm surfaces generally is to use radiant heating either from a point source like a stove or fireplace or from a large surface area as in under floor heating (the subject of a forthcoming blog post). This tends to heat the surfaces and objects in the room without heating the air in between – just like the sun.
Air Temperature – the effect on fatigue, health, and sleep
Air temperature dominates our common understanding of temperature yet it is only one part and unfortunately the most problematic. In trying to keep warm many people simply increase the temperature which in addition to being only partially successful tends to exacerbate health problems.
Excessively warm air temperatures reduce concentration and performance, increase pulse rates, skin moisture, and likelihood of fatigue. Warm air heating and air conditioning have also been associated with common colds, dried mucous membranes, headaches, irritability and weakened circulation. Cool air on the other hand tends to have the opposite effect and aids deeper breathing which is particularly important when sleeping.
Warm Air Heating Creates Problems
Warm air is lighter than cold air so rises and collects below ceilings. This can be very helpful in summer where high level windows and vents readily exhaust air and aid comfort but in winter it means that most of the warmth is where people aren’t. This means more heat has to be generated to swell the warmth down to where people are operating (or move the warm air down using fans) which leads to excessive heat input and significantly excessive warmth to the head whilst feet remain too cold. This is exactly the wrong way round for human comfort and health.
So all in all warm air heating makes for a sorry tale and since all heating systems will heat the air to some extent it is unavoidable. Clearly though we can seek to minimize this whilst optimizing the benefits of cooler air in the process.
Air Movement –ideally a small degree
Moving air, however warm, will tend to cool the body by evaporation. There is something strangely counterproductive of first heating the air and then moving it and by doing so creating a cooling effect.
What is needed for health is a small degree of air movement. Think of a warm day and a light breeze and the truth of this is apparent. Too little air movement and we cannot get rid of our moisture (sweat), respiration is impaired, and we get warm and tired. Too much air movement and we will get cold. Bear in mind however that occupants sitting for long periods will appreciate less air movement while those working manually will need more. Air movement is also related to the airtightness of the building and to the ventilation strategy.
Excessive air movement tends to lift and circulate dust which creates further health problems.
Negative Ions for Health – Abundant by Water
In overly simple terms positive ions are relatively bad for respiratory health whilst negative ions are relatively good. Think of yourself by the side of a mountain stream with fresh gurgling running water for an image of an environment with higher negative ions and you can get a sense of this. In forced air systems the movement of air creates friction in the ducts and positive ions in the process. Positive ionization of the air also creates problems for the respiratory system.
Heat Emitter Surface Temperature
Fires and hot surfaces like stoves and, the inaptly named, radiators (which emit their heat through convection not radiation)have the effect of scorching dust which is unhelpful for health and more significantly they stir up air movement creating convection currents which then move all that scorched dust around.
Happily low surface temperature emitters which reduce this problem have become more common largely due to health and safety concerns regarding children and other vulnerable people burning themselves. The problem is that radiation is more effective with a higher temperature so, to achieve the same heat input, these heat emitters need to be larger to make up for the lower temperatures.
Temperature Monotony on the Starship Enterprise
Walk into a cool Cathedral in southern Spain on a hot summer’s day or enter a warm room after a snowball fight and you’ll appreciate the welcome effect of moving into a zone with a different temperature. Passing between areas of different temperature is invigorating.
Conversely experience suggests that having all the rooms the same temperature has a deadening effect on the body as an organism. It may be ok for Captain Kirk and Dr Spock but for you and I are more comfortable with some rooms warmer and cooler than others.
We are ideally looking for a system that uses radiant heating creating warm surfaces and slightly cooler air with a little movement and which allows for a different temperatures in different rooms. It needs to be quiet and easy to control working well with the ventilation system.
As we make our homes more airtight the quality of the air and the warmth becomes more important still. Energy efficiency and healthy buildings can be mutually supportive with good design.
I intend to write about under-floor heating shortly.
Author: John Wolfendale
Bio: John is a founder of Eco Vida and is passionate about bringing modern design and construction practices to Spain. He believes a home which is warm in winter and cool in summer is largely a matter of design and selective use of materials. He is British and a Chartered Surveyor with 18 years experience living and working in Spain.