Articles and whitepapers

Residential Energy Management (4/7/2005)

By Dave Robinson, Sensible Heat

Energy management systems have been in use within non-residential buildings for over thirty years. Born on the back of the first energy crisis, these systems (sometimes called Building Energy Management Systems, or BEMS) were originally based on commercial minicomputers with 'dumb' peripherals, and were later developed to have purpose-made controllers or 'outstations' with their own dedicated embedded microprocessor. The purpose of these systems was to save energy, principally by controlling the HVAC (Heating, Ventilation and Air Conditioning) plant better. Most of the energy used in, say, an office building, is for heating, cooling and ventilating. The next biggest culprit is lighting.

If these elements can be controlled more effectively, energy, and hence money, can be saved. Nowadays, of course, there is a much more compelling reason to control energy usage; heating and cooling of buildings accounts for around a half of all of the UK's CO2 emissions, and we need to cut this dramatically.

Saving energy

In domestic houses, the energy usage pattern is not dissimilar to an office building. Space heating and hot water generation still take up the lion's share, yet most houses are still fitted with crude, energy-wasting timeclocks and thermostats. With a built housing stock of 22 million, and potential energy savings of 25-30% by fitting better controls, this has to be an area worth exploring. We can save money, CO2 emissions, and be more comfortable - surely it's a no-brainer!

How can savings of this magnitude be possible? As is often the case, the principles are very simple, but the detailed implementation is a little more involved. Basically, we need to ensure that heating systems are only running when they need to be so that we are not heating parts of the house unnecessarily, and that when running, the rooms are heated to the correct temperature - no more, no less.

Temperature control

If we look at temperature control, we see that the typical thermostatic control of most houses allows the temperature to wander up and down by one or two degrees. This is because the thermostat has inherent hysteresis. It only switches the heating off when the temperature has already risen above the desired temperature - far too late! It is reckoned that a one degree decrease in temperature setpoint can save around 10% of the energy costs, so if we can control temperature closely, we can prevent overheating, increase comfort, and use less energy.

Zoning

To achieve this, we need to do two things. Firstly, we must 'zone' the house into multiple zones - ideally a zone per room - allowing each room to be individually controlled. Secondly, we need to employ continuous control, where the temperature is measured electronically and compared with the desired temperature, and a complex algorithm (often PID, or fuzzy logic) decides how much heat output is required to offset the heat losses.

The timing of the heating is also deceptively complex. Often, a conventional timeclock will bring on the whole house heating at once, when probably only a handful of rooms are being used at any one time. Also, rooms need to be at different temperatures at different times of the day. Reception rooms should be cool during the daytime, warmer in the evening when you're sitting still, and cold overnight. Such control is not possible using conventional thermostats, so they tend to get set to the highest, 'evening' temperature.

The Hometronic Radiator Controller makes each room into a zone with no wires or plumbing changes

The classic case of the heating being left on during a holiday or even a short absence has got even worse with the rise in popularity of underfloor heating. These systems take so long to heat a cold house that owners are unwilling to wait to be comfortable, so they leave the heating on permanently.

These problems can be solved by proper zoning, and by providing easy-to-use interfaces for the user, so that they can preset times and temperatures, and also be able to set the 'guest mode' which would liven up the guest rooms for visitors, or the 'vacation mode' for setting holiday dates. Depending on the building and the plant installed, other advanced techniques can be used. These include 'optimum start' where the heating starts earlier automatically on a cold day, or 'weather compensation' for radiators, where their water supply runs cooler on mild days.

Implementation

So how can we implement all of these features in a house? Of course houses can be, and have been, fitted with industrial BEMS. Often, consulting engineers more familiar with commercial buildings, will specify these systems for a house, but the problem with this approach is that these products are designed with commercial buildings, and their operators, in mind. You end up with large industrial steel control panels, covered in lamps and switches, looking more at home in a power station than in someone's house. Also, the user interfaces are designed for engineers, and are completely unsuited to the average homeowner.

Fortunately, a new generation of product has emerged to fill the gap between industrial BEMS and traditional timeclocks. Several manufacturers are addressing the residential sector, either with adapted BEMS products, or purpose-designed systems. Siemens Smart Home Technology, smartKontrols, and Sensible Heat's Honeywell Hometronic are all examples of systems that specifically address the issues of size and appropriateness for the home, and user interface.

The Hometronic Manager - an appropriate user interface for a home

Some of these systems allow remote access to the system, by phone or Internet, and some allow interfacing with other systems, such as intruder alarms, lighting systems or touchscreen controls - these are some of the things to be considered when choosing a system. One of the systems, Hometronic, is wireless, which may be a consideration if cabling routes are difficult.

The Hometronic Voice Interface allows owners to phone their house to turn on the heating

Choosing the right professional

It is not just the technicalities of the product that you should consider. Make sure that the company you chose is used to working in the residential environment, and make sure they are familiar with both high-tech systems and the boring details of plumbing.

It is vital that the controls specialist has a complete understanding of HVAC plant, and also knows about other technology within the house. Ask for references - if your prospective supplier seems to have worked on a lot of schools, hospitals and offices, or doesn't know a Crestron from an AMX, walk away - otherwise it will end in tears.

Remember that control of HVAC is unlike just about any other form of home automation, in that the controls company does not get to specify the plant that it is controlling - most of the time, it has already been installed before the company joins the project!

Dave Robinson is the Managing Director of Sensible Heat - manufacturer of HVAC controls and integration products, distributor of the Honeywell Hometronic wireless home automation system, and green energy consultant.

www.sensibleheat.com