Heating in the time of a credit crunch
Specifying energy efficiency — Peter Gammon
With fuel prices at record highs and dark thoughts of recession, Peter Gammon considers what specifiers of heating systems can do to make the best of the current tough times.It’s no good looking at newspapers or websites for comfort. Wherever you look — in the real or virtual worlds — the news makes for miserable reading. Housebuilders’ shares are dropping quicker than Gordon Brown’s popularity. Budgets are being squeezed tighter than an Olympic diver’s Speedos, and the financial problems of the credit crunch and rising fuel prices combine to make a very different world that of a year or two ago. But how does this affect the specifier or heating engineer? Is there anything we can do that will make a blind bit of difference? And if there is, what’s in it for us? Well, I like to think of myself as a glass-half-full type of chap. There are several things one can do to cut down energy bills — and how a system is specified will make a great deal of difference. If you take the time to consider everything from the boiler set up to controls and insulation as well as everything in between, you will end up with a system that is efficient and, if you are retrofitting, is liable to show decent energy savings and a reduction in fuel bills. Let us start with the system design. I am probably teaching grandmothers to suck eggs here, but if you can run a system at lower temperatures, you will to get more bang for your bucks (I am assuming that you are going to be using condensing boilers). For example, if you choose underfloor heating for space heating, you can run the system at a lower temperature. A traditional heating system with radiators typically runs at 82/71°C flow/return, whereas underfloor heating only needs temperatures of nominally 55/45°C — which increases boiler efficiency by 3 to 7%, depending on load. Underfloor heating is all very well for a new-build property but it can also be retrofitted into an existing building using a floating floor; you just need to be mindful that a floating floor will reduce floor to ceiling heights by 50 to 75mm. A very important aspect of any and every installation is the turn-down ratio of the heat generator as design conditions apply for an extremely small fraction of the time that the system is in operation. In a commercial building which keeps normal office hours, the heating system will be seldom, if ever, be working under full design conditions. If the heat-generating plant (boiler) cannot turn down sufficiently to meet the typical load, you may be storing up problems with the kit itself through rapid cycling and wear and tear — leading to an increased chance of breakdown and higher maintenance costs. That is where a cascade or modular system comes into its own. As we have already said, design conditions dictate boiler size. However, research shows these conditions are met only 2.5% of the time, and the load on a building can be as low as 15% of the design figure. On milder days in the heating season (which seem to occur more and more frequently), when there is reduced demand for heat output from the system, it should be able to respond by reducing the amount of heat energy delivered. With one or even two larger boilers, the kind of turndown needed is much trickier to reach than with a cascade installation of several boilers. One boiler might give you a 5:1 turndown ratio, but if you have five in an installation, you get a 25:1 turndown ratio. The closer you can match the heat generation to the load, the more seasonally efficient the system becomes — saving fuel and reducing emissions and enhancing the reliable life of the plant. In addition to modulating power output, controls offer so much potential to reduce energy consumption. Wherever possible include room temperature controls; do not just rely on controlling the source temperature. From sophisticated room sensors with room influence on the power output of the system to basic thermostatic radiator valves, all improve energy efficiency — provided, of course, that they are set correctly. Tamper proof or lockable settings are sometimes the order of the day).
Cascading a number of boilers in an installation enables a high turndown ratio to be achieved at times of low demand.
For larger commercial buildings, the principles of fuel economy are the same — it is just that some of the controls are more sophisticated. They range from simple thermostatic controls or weather-compensated flow temperatures (direct-on-boiler weather compensated temperatures are best for optimum condensing boiler efficiency), to full computer-controlled building management systems — which control not only the heating, but lighting, air conditioning, security and fire systems. The more a building can be divided into zones from a control point of view, the more comfortable and energy efficient it tends to be. Ethernet linkups enable buildings to be monitored remotely over the Internet so that building services engineers can manage several sites at once. If you are retrofitting boilers to old heating systems be mindful that the old system and boiler/s were probably considerably oversized. Do not just fit like size for like size; a boiler that is not oversized and closely matched to the load will perform more efficiently. Also, it may well be possible to operate the old existing heat emitters at a lower temperature (due to their over-sizing) and thus instantly seeing improved boiler efficiency. By specifying energy efficiency into the system, you will reap the benefits when the fuel bills land on your desk. Specifying boiler plant need not focus on what has gone before. To achieve the best performance and efficiency it is worth taking the time to find innovative solutions — whether a new set of controls, a cascade modular installation, or even district heating and heat interface units. By embracing innovation, you will be looking towards a greener and more fuel efficient future. Peter Gammon is technical manager with MHS Boilers.