Do you ever have to explain three-phase electricity to people? This five-minute video is a kitchen-table demonstration using pipes, water, syringes and a crank (two if you count me).
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Category Archives: Energy technologies
Estimating savings from building-fabric improvements
If you improve a building’s insulation, or reduce its ventilation rate, the resulting energy saving can be estimated using simple formulae in combination with relevant weather-data tables. In the case of an improvement to insulation of an individual element of the building envelope, the approximate formula for annual fuel savings is
0.024 x (UOLD – UNEW) x A x DDA / EFF (kWh)
where UOLD and UNEW are the original and improved U-values (W/m2K), and A is the area of building element being improved (m2). EFF is heating-system efficiency, for which it would be reasonable to assume a value in the range of 0.8 to 0.9, reflecting the fact that 10-20% of the fuel used is accounted for by combustion losses.
DDA meanwhile is the annual heating degree-day figure, which is a measure of how cold the weather was in aggregate. Degree-day totals tend to be higher in the north and lower in the south; and they also depend on the outside temperature below which a given building’s heating needs to be turned on (the ‘base’ temperature). Selected totals are given in Table 1 for various regions and base temperatures. Buildings with high space temperatures and low casual heat gains have higher base temperatures, implying higher annual degree-day totals and thus bigger expected savings for a given improvement to their insulation.
Turning to the effect of reducing the building’s ventilation rate, we need to know the reduction in air throughput, RDV. If we express RDV in m3/day, the annual energy savings are given by this approximate formula:
(0.008 x RDV x DDA) / EFF (kWh)
DDA and EFF have the same meanings as before.
Use for air conditioning
The same techniques can be used to gauge the effect of reduced cooling load. In this case we use cooling degree days (examples in Table 2) and EFF is likely to be in the range 2 to 4, representing the chiller coefficient of performance. Saving one kWh of cooling effect saves much less than a kWh of electricity.
Base temperatures
The base temperature for heating depends on the temperature set-point, the construction of the building, how it is used, how densely it is populated and how much casual heat gain it experiences from lighting and equipment. It is invariably below the internal set-point temperature. How far below can be determined in various ways but there would typically be about 4°C difference.
Similar considerations apply to cooling: the cooling base temperature is the temperature above which it becomes necessary to run air conditioning. If you know air-conditioning is used throughout the year, a very low base (say 5°C) is appropriate. Otherwise something of the order of 15°C could be a reasonable assumption.
Table 1: Annual heating degree days1
| Base temperature: | 20°C | 15°C | 10°C |
| South West | 3,189 | 1,576 | 503 |
| Midland | 3,632 | 2,033 | 860 |
| N E Scotland | 4,075 | 2,355 | 1,003 |
Table 2: Annual cooling degree days1
| Base temperature: | 25°C | 15°C | 5°C |
| South West | 2 | 233 | 2,386 |
| Midland | 6 | 274 | 2,111 |
| N E Scotland | 0 | 111 | 1,649 |
1 The full tables can be downloaded from www.vesma.com. Click on ‘D’ in the A-Z index and look for ‘degree days’.
Voltage reduction: the short answer
I am somewhat conscious of taking my life in my hands in this issue, but as so many readers have asked me what I think about voltage “optimisation” (or reduction, to use a more accurate term), let me answer the question with the following three guidelines, which apply to everything from heating and lighting to motive power:
1. If the equipment is regulated in any manner, don’t expect voltage reduction to save energy.
2. If it is unregulated and you don’t mind reduced output, voltage reduction will save energy.
3. If it is a thermal application used on an intermittent cycle, voltage reduction will have a perverse effect, increasing energy consumption.
How to waste energy No. 4: compressed air
1. Use compressed air for dusting off overalls, sweeping the yard and other cleaning duties. This not only wastes energy but blows debris into people’s eyes.
2. If you have individual applications that require a higher pressure, run the entire system to satisfy them rather than fitting local boosters.
3. Set overall system pressure as high as you can (check that the safety valves are lifting frequently). As a rule of thumb, every 2 psi increase in operating pressure requires an additional 1% energy.
4. For low-grade duties such as tank agitation, use clean dried compressed air at high pressure rather than fitting local blowers.
5. Locate air inlets in the hottest place possible – remember every 6C increase in temperature adds 1% to the electricity consumption.
6. Never clean your air filters and avoid fitting low-loss types.
7. Make sure you do not dry the air.
8. Allow all your compressors to run in parallel, sharing the load however small.
9. Do not shut the system down if the premises are closed at night; but if you do, empty the air receiver at the end of the day so that it needs to be repressurised in the morning.
10. Leave air-receiver drain cocks cracked open.
11. Bypass the air receiver so that the compressors have difficulty matching the load and need to start and stop frequently. This is a marvellously inefficient mode of operation, and abrupt swings in pressure will also help to maximise the number of leaking joints and fittings.
12. Maximise pressure drops in the distribution system by undersizing all pipework.
13. Ignore leaks: fixing one probably causes another to appear somewhere else. If you have a routine for tagging and repairing leaks, do not repair any that people find. As well as wasting energy this will discourage people from reporting air loss.
14. When specifying new equipment, give preference to models that continuously vent air. Use air tools if electric equivalents are just as good.
15. Look for opportunities to use compressed air inappropriately. Dusting off overalls may not waste enough; try using it for cooling motor bearings that are running hot, or to cool people working in hot locations.
16. Do not recover free heat from compressor exhausts if it is possible to use heat from a boiler system (or better still, electric heaters) instead.
How to waste energy No. 3: lighting
1. If your light fittings are the type with translucent diffusers, fill them with dead flies.
2. Avoid replacing tungsten-filament light bulbs with LED equivalents. Although it is now illegal to sell most general lighting service (GLS) filament lamps, one can still buy “rough service” equivalents which have the great advantage of being even less energy-efficient.
3. Keep your external lighting on 24 hours a day. This encourages a culture of not caring about leaving things running when idle, and will help waste many times more energy than is used in the lights alone.
4. Also keep your internal lights on continuously, not least because doing so will increase the demand for air conditioning.
5. Provide excessive light levels in working areas and try to ensure that corridors and stairwells are even brighter (this removes one of the vital cues that prompt people to turn lights off when they leave empty rooms).
6. Be careless when specifying automatic lighting controls. Choose the wrong sensor technology, so as to maximise nuisance switching. This has a dual benefit – it encourages people to override the control, and it also antagonises them so they won’t cooperate with other energy-saving initiatives.
7. In shared workplaces, paint over any labels identifying which switch controls which zone.
8. Choose automatic lighting controls with remote control handsets that cannot be understood without training. Then lose the instructions and the remotes.
How to waste energy No. 2: automatic control of buildings
1. Set your frost-protection thermostat at too high a temperature.
2. Override your time control to run the plant continuously.
3. Set heating controls for maximum air temperature. The aim should be to make it so hot that occupants are forced to keep the doors and windows open, increasing the heat loss.
4. Alternatively, place a baked-potato oven under the space temperature sensor. This will hold the heating off and encourage people to bring in electric heaters.
5. If you have adaptive optimum-start control, set the timings as if it were a conventional time-switch (i.e. with start of occupancy at the same time you would previously have asked the plant to start up).
6. Also if you have adaptive optimum-start control, set a target temperature above the daytime control setpoint. The control will add more and more preheat every day because it never achieves the target temperature.
7. If you have air conditioning, set it to cool to a lower temperature than your heating, so that the two systems run simultaneously providing perfect comfort at infinite cost.
8. If you have humidity control, set it for the narrowest range conceivable. This will ensure you are nearly always either humidifying or dehumidifying.
9. Remove or jam the linkages on valve and damper actuators.
10. Do not commission your building energy management system; do not document the control philosophy or agreed settings; and as a backstop, lose the operating manuals.
How to waste energy No. 1: motor-driven equipment
1. When a motor fails, have it rewound by a cowboy outfit, as this will reduce its efficiency.
2. If you need to replace a motor, use the cheapest and least efficient unit available (preferably oversized). Efficiency standards of new motors are being continuously improved, so you may need to shop on eBay.
3. Shift motors slightly on their mounting plates so that any drives and couplings are misaligned.
4. Ensure that drive-belts are slack. On multi-belt drives it can help to remove some belts. If possible, use the wrong kind of belt for the pulleys fitted.
5. Change pulley ratios to drive fans and pumps at higher speed: on centrifugal fans and pumps, a 20% speed increase adds over 70% to the load.
6. Neglect lubrication of bearings and gearboxes.
7. Allow equipment to run continuously, whether it is needed or not. This has the added advantage of accelerating wear and tear, and reducing your power factor.
8. When the driven equipment is decommissioned, at least leave its motor behind, energised and running.
9. In dirty environments, do not clean any debris off motor cooling air inlets. The extra resistance to air flow will increase mechanical losses in the motor and, as a bonus, accelerate its failure by causing it to overheat.
10. In situations where the mechanical output of a fixed-speed motor is controlled and regulated, run the motor below its rated voltage in order to increase the motor current and associated copper losses.
Duty-standby rotation
One of my clients, who operates computer data centres, asked his monitoring and targeting software supplier to conduct some pilot analyses using daily data. Cusum analysis of one particular circuit, which was feeding computer-room air cooling (CRAC) units, threw up an interesting observation: energy performance had been toggling between good and bad on the first of every month. This fact had been masked by the weather and variations in the quantity of energy consumed in the equipment racks, but once revealed, it was traced to the fact that they were alternating two banks of CRACs on a monthly cycle. In situations like this, it pays to change the regime so that preference is given to the more energy-efficient plant. This has the secondary advantage that the standby set will have more maintenance life left in it when the lead set fails. Cusum analysis is very good at providing insights like this, which is why I give it prominence in my training courses on monitoring and targeting.
The other place one finds opportunities for instant savings is multi-boiler heating systems, where, too often, the firing sequence is deliberately rotated to give each boiler the lead and even out the wear. Apart from making no sense in terms of risk management (when one fails, all the survivors will be equally clapped-out) it also misses the opportunity to favour the unit with the highest combustion efficiency, and thereby consume less fuel for a given output of useful heat. Anyone unfamiliar with combustion efficiency and the opportunities that it offers can read up in the A to Z guide at www.vesma.com.
Combustion tuning is a good (and frequently-overlooked) opportunity for nearly all fuel users.
Super-thin insulation
Super-thin thermal insulation is in my sights at the moment. There are two categories: (a) multi-layer foil and fibre; and (b) paints or paint additives. The insulating effect of multi-layer systems is basically equal to the same thickness of whatever insulating fibre they use, but there is some additional advantage where they are installed with an air gap either side, since they create an extra cavity which has a certain thermal resistance. Their reflective foil will impart additional thermal resistance by preventing radiation from the hot to the cold face of the cavity. But note, however, that after filling with ordinary fibre, the hot and cold surfaces of the cavity can no longer see each other, and heat transfer is solely by conduction. So BOTH techniques eliminate radiative transfer across the cavity and the foil therefore imparts no advantage.
Insulating paints meanwhile, even if composed of material with high thermal resistivity, will have totally negligible effect because the insulating layer is microscopically thin (under 0.3mm by my calculations, based on coverage data in the advertisements). Claims that their ingredients reflect heat are unsound because those so-say reflective materials are buried in the paint layer; to reflect heat the SURFACE of the paint would need to act like a mirror to infra-red radiation.