Nowadays the public is very familiar with the use of Air-to-Air heat pumps to provide a permanent heating solution to our homes. They are easy to operate via the very familiar remote control mechanism; they can be programmed for convenient operating times and temperatures; they circulate the room’s air volume better than an electric panel heater; they do not release undesirable emission products into the space from their fuel; they are relatively easy to retro-fit to existing dwellings; and they provide a quick way to raise temperatures to comfort levels.
For the majority of households there is a need for a rapid warm-up in the morning before the family goes its various ways, and then for adequate heating from late afternoon until everyone retires in the evening. Yes, there are dwellings with occupants regularly present throughout the day but these are in the minority. Most family homes have one parent working full-time and the other at least in a regular part-time position away from the house. The homes of occupants without children to care for are very often empty throughout the full working day. For these situations, Air-to-Air heat pumps are ideal as an intermittent heat source.
The recent experiment with the Tight-5-Million in enforced lock-down has shown the employer and employee workforce that there is more than one way to organise our commercial world — people can be trusted to work productively from home without a manager breathing down their necks (though of course, manual work such as construction and manufacturing cannot be undertaken from home). Despite the country having now been (practically) at a pre-Covid-19 level for more than one and a half months, recent surveys show that Auckland traffic flows, bus and CBD café patronage, are still significantly below those of 2019 and opinions are being expressed that working from home is a very viable option. I understand that forward-thinking group builders, and even Kāinga Ora, are actively considering the implications of a significant demand for dwellings which can accommodate ‘working-from-home’ activities. It would be unwise to assume that all will return to the past normal.
While the heating aspect of dwelling design is but a small part of the process, the decisions made at the early stage become difficult and expensive to fundamentally change over the lifetime of the building. In the 1960s electrically heated concrete floors were all the rage, and it wasn’t until the 1970s that insulation batts were beginning to be installed. If Society is to make a substantial move to working from home then serious attention must be given to the appropriate heating methods.
At present, fast-reacting appliances are suitable for most domestic situations but, if (when) there is a move for some of the home occupants being permanently present for most of the day, are they the most efficient solution? Now is the time for a fundamental discussion of the nature of our future housing stock, and for more than just heating.
The Residential Tenancies (Healthy Homes Standards) Regulations 2019 require minimum heating levels for the main living room using an Air-to-Air heat pump (or electric heater if the demand is low enough). While this is appropriate for the existing housing stock, I can see this morphing into a mandatory heating method for future dwellings unless there is informed and objective discussion, especially if only vested-interest industries are consulted.
While using heated air is an easy and fast-acting method of warming occupants, it has the primary disadvantages of creating draughts, requires careful placement of the indoor unit to give even coverage, and there is a need for continual maintenance for effective operation. The location, size and type of the outdoor unit are also critical for proper operation. The most effective form of heating is even distribution from the floor but, unless done properly, this is not appropriate for the Oceanic Climate of most population centres and our normal daily occupation profile.
If there is a significant move to working from home then hydronic heating systems for concrete floors become worthy of consideration. However, only if they are designed and constructed in an intelligent manner, unlike most which are now being installed. In earlier EBOSS Detailed blogs I have commented on the thermal performance of concrete floors in general, and more specifically the effectiveness of present slab-edge insulation details, especially when applied to a heated slab (see Is Slab Edge Insulation as Effective as it Seems? and Slab Edge Insulation: An Interesting Experiment for more details). A portion of the consulting work I do at present involves my viewing a lot of foundation/slab/wall junction construction details. Although some have slab edge insulation, which may be okay for an unheated floor, in my opinion, they are totally inadequate for a heated slab. A heated floor slab (especially with the growing awareness of climate change and the need for energy savings), must be constructed as a separate thermal mass fully insulated from the concrete foundations and ground especially if the surface has carpet which will reduce the heat transfer.
We need to widen our thinking from considering heat pumps as only air/air unit on the lounge wall. The water for the hydronic system needs itself to be heated. The usual way would be by a fuelled boiler or an air/water heat pump. An Air-to-Water heat pump, backed by solar pre-heating of the cold water, is far more energy-efficient than an electric or gas boiler. After insulation, area zoning is the most vital aspect of the planning of a hydronic floor heating system from an energy-saving point of view.
Along with a fundamental review of how dwellings are used, Covid-19 has shown us that 'Working-from-Home' is growing fast which will necessitate a reconsideration of how we heat our houses.
Through EcoRate Ltd – Architect, I provide objective independent thermal performance analysis and advice on sustainability matters, to architects, designers, builders, manufacturers, and others in the construction industry, including those proposing to build a new home. I am also a Homestar Assessor.
Image by Bonnie Kittle, Unsplash