There is something magical about that warm glow underfoot. What are the advantages of under floor heat delivery over conventional radiators? Is it suitable to the climate in Spain?
Firstly the only under floor heating systems that are of interest to us are those that pass water through coiled pipes. As far as we are concerned electrical under floor heating has drawbacks that make it undesirable from an environmental viewpoint such as the high CO2 emissions associated with using main electricity and also the generation of electrical and magnetic fields.
Secondly it’s important to choose your heat delivery system in conjunction with everything else. The building structure type, insulation levels, airtightness, heating settings, furnishings etc will all affect the speed with which internal temperatures respond to a drop in temperatures outside.
The reaction time of your heat delivery system has a great effect on the comfort level of the occupants and the energy consumed. A lightweight building will be more responsive to changes in temperature than a heavyweight building. This cuts both ways – more responsive could mean that the building is equally as responsive to falling outside temperatures as it may be to rising internal temperatures from the heating. A heavyweight building will be slower to respond and gradually reacts to the seasonal changes rather than day to night fluctuations.
Micro Climates In Spain
The micro climate in Spain is enormously variable. We have quite a different situation where I live close to the city of Granada, and in the mountains of the Sierra Nevada, to that only forty minutes away on the coast. However in both situations during the spring and autumn you can experience quite sudden and wide ranging variations in temperature: quite hot turning to quite cold overnight perhaps lasting a few days and then turning back again. This is an important consideration to bear in mind when choosing the heat delivery method for your building.
Types of Wet Under floor Heating
There are basically two types of wet under floor heating: heat store or fast delivery
Heat Store Under floor heating systems are those where the pipes are laid within a relatively thick concrete or lime concrete slab which would be insulated below and around the perimeter. These systems are slower to heat up and slower to cool. The speed of cooling will of course be influences by the temperature and airtightness of the room
Fast Delivery systems are those that have pipes laid on top of insulation either in a thin screed or specially formed insulation containing trenches for the pipes to sit in beneath a thin screed or timber flooring.
Logic would suggest that the former would be most suitable for a heavyweight building and the latter for a light weight building that need a faster response. However there is no reason why they cannot be mixed and many light weight buildings would actually benefit from the addition of a heat store
Floors Versus Radiators as Heat Emitters
Heating a space sufficiently to maintain a comfortable body temperature without lowering the humidity so much as to cause discomfort can best be achieved by a large area of radiant surface. If the surface area is large, such as a floor for example, then the temperature required to effect change can be lower.
Radiators (remarkably inaptly named) only emit about 15% of their heat by radiation. The rest is achieved by convection. Because conventional radiators are generally quite small in comparison to the room to work effectively they need to deliver hot water at temperatures above 60 degrees C. This creates localized hot spots and the convected air rises to the ceiling, flows across the top of the room, and down the other side as it cools. The convected current will also carry dust and will lower the humidity of the air both of which can cause problems for allergy sufferers.
Under floor heating comprises a large gently radiating surface which only needs to be a few degrees warmer than the air in the room using water temperatures of between 45-55 degrees C. Because of this the differential between floor and room temperature is usually so small that convection is avoided.
Furthermore radiant heat energy works like sunlight as the heat from the floor warms the occupants directly as well as through the air. That’s a very comfortable feeling. And comfortable conditions can be achieved using much lower water temperatures thus saving energy and money, without drying the air, and with no localized hot spots in the room.
Under floor heating systems can use a variety of heat sources: ground or air source heat pumps, bio mass boiler etc. They are low maintenance. They are generally no more expensive to install than a comparable radiator system. Virtually any kind of floor covering can be used with under floor heating.
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.