HEATING & COOLING
Introduction
What is Thermal Comfort
Thermal comfort is a condition of mind that expresses satisfaction with the thermal environment. Basically your brain tells you if your body is happy with the temperature, humidity and ventilation (think breeze or draughts) of the space you are in.
We want all Healthy Homes to be thermally comfortable at all times.
An example of thermal comfort is what happens on a hot, still day. You might feel horrible, sticky with sweat and you just can’t cool down. Then a cool breeze blows through and suddenly you feel more comfortable. The temperature (hot) and humidity (sticky) have not changed, but the ventilation (breeze) has and so has your comfort. Therefore, in order to have a thermally comfortable (and thus healthy) home we need to have temperature, humidity and ventilation all in the healthy zone. You can’t have two right and one wrong.
Thermal comfort is important for health and general wellbeing. If you are uncomfortable it stresses your body, diminishing your body’s ability to fight off illness.
Temperature
Temperature is a component of thermal comfort. Nobody likes to be too cold, just like we don’t like to be too hot.
When you are ‘too hot’ your body has to work hard to try and cool you down. This places stress on your body and in extreme situations you can become unable to cool down to a comfortable level.
Babies and the elderly are at the greatest risk of overheating. We all know to not leave our children (or animals) in a locked car in summer, but how many of us realise the same holds true about a hot bedroom? Cot death is linked to high heat and it is therefore really important to understand how warm your baby’s room and cot/crib is.
Research shows a 2 to 3% increase in mortality in adults for each 1°C rise in temperature above 27 to 29°C*.
For children the mortality is 50 to 100% higher than adults**
But how many people think about this when designing housing? How many think about the ability of the house or room to be cooled during a summer heat wave? Or having moveable, external, shade devices to stop solar gain through the windows? These are questions that we are yet to deem important.
But in a warming world, not thinking about these questions could lead to extreme occupant discomfort in the summer. Those large west facing windows might provide a fantastic view, but will people even be able to sit in that room during the height of summer?
‘Too cold’ is also unhealthy and extreme cold can cause illness and death. Cold air inflames lungs and inhibits circulation, increasing the risk of asthma attacks, worsening chronic obstructive pulmonary disease and infection. Cold also induces vasoconstriction, which causes stress to the circulatory system that can lead to cardiovascular effects, including heart disease, strokes, and death.
So what temperature should housing be at?
The World Health Organisation22 has recommended a temperature range of 18° to 24°C to be maintained.
It is really important to maintain temperature within a consistent range at all times, as varying temperatures will results in varying relative humidity (as relative humidity is relative to temperature). In many countries around the world there is a culture of intermittent heating to raise (or decrease) temperatures only when spaces are occupied. However, whilst rooms might not be occupied by humans all the time, other things live in houses. Dust mites, mould, bacteria and viruses can all live in our buildings and intermittent heating and varying temperatures and relative humidity, allowing them to not only survive, but thrive.
This is why we must design to keep temperatures within the healthy range of 18° to 24°C AT ALL TIMES!
22https://www.who.int/publications/i/item/who-housing-and-health-guidelines
Windows play an important role too. See Windows section.
Air Quality is also very important because damp air is much harder to heat. See Ventilation section.
Regulatory Requirements
The Healthy Homes legislation requires that landlords must provide one or more fixed heaters that can directly heat the main living room. The heater(s) must be acceptable types, and must meet the minimum heating capacity required for your main living room. https://www.tenancy.govt.nz/healthy-homes/heating-standard/ states that “The World Health Organization (WHO) recommends a minimum indoor temperature of 18˚C. By installing heating that can reach this temperature on the coldest days of the year, tenants will be able to keep warm all year round.”
Heating Types
Central Heating and Cooling
People living in the UK, Europe and North America don’t even wonder about it. They know that Central Heating is the preferred source of heating.
The most cost-effective form of heating is from the sun. ‘Free’ heat from the sun can be optimised with good envelope design, window selection, placement, and insulation.
The next best method of heating a new home, is pipes in the slab connected to an air-to-water heat pump This arrangement can also be used to cool the home in summer. The combined total running and construction cost means that this can be the lowest cost way to perform these tasks. In other words, you will have lower total monthly costs than other forms of heating.
In Christchurch for example, in the winter months a typical heated slab system will store about 1kWhr of heat for each m2 of floor area. This means that a 200m2 house will store about 200kWhr of heat energy in its floor slab over a house without a heated floor. To store that amount of heat energy in batteries would mean 20 x 10kWhr batteries = $200,000. That wouldn’t make economic sense, but it shows the value that you create in a heated floor slab system.
Another way would be to install Radiators as is common in the UK. These can also be heated via heat pumps or via gas or diesel boilers.
A third way is Ducted Heat Pumps. This is not really suitable for heating a house well. However, it might well afford some reasonable cooling. Heating with air requires air to be moved around which creates draughts.
Air-to-air Heat Pumps
While these are quite efficient in producing heating and cooling, they have some disadvantages. They blow air, which can be a negative when operating in winter. They also have to defrost during winter in cold climates, and cannot produce heat while doing so. They are also limited in their ability to treat more than one room space.
Suppliers
https://warmth.nz/what-we-do/ provide Cost-Effective Home Energy Solutions in the form of affordable, in-slab underfloor heating, cooling and heat pump hot water to new builds in the South Island of New Zealand.
Recommended Healthy Home guidelines for Heating & Cooling are set out in the table below:
