Energy Efficiency, Total Life Cycle and Free Cooling in New and Existing Cooling Systems - Transcript
One of the points that David pointed out is the issues with carbon dioxide levels and the effect that’s having on the environment, and we hear that everyday. Even this morning, I was just listening to the TV news and it was talking about the level of CO2 in the environment and the effect that’s having on the temperature. It was interesting stuff, actually. Despite the fact that we have seen this growth over the last few years, in terms of annual temperature – we’ve seen that start to increase over the last hundred or so years – it is now starting to level out, and I’m not quite sure why that is. Despite the fact that the CO2 level now is at record proportions, temperatures seem to have been stabilising. Scientists are saying that that is because heat is starting to go into the sea, and the sea is starting to warm up. That falls in with the fact that we’re losing all these icebergs. They’re slowly disappearing, but it’s fair to say that we’re still not quite sure why – all we know is that CO2 levels are increasing, and legislation is being put in place to try and tackle that.
This part of the presentation is all about energy efficiency, and you think "what’s that got to do with CO2?" Well, of course, the drive is to try and reduce the amount of electricity that we’re using, as well as things like gas and the amount of energy and CO2 that we’re chucking into the atmosphere, which is then potentially causing this heating problem. So, there is a good environmental reason for looking at energy efficiency, and there are a lot of corporate social responsibility statements that are saying “we’re going to reduce our carbon levels and the amount that we’re producing, get our carbon footprint down, etc.” And that’s a very good, responsible approach that many businesses are taking for the environment. Also, at the end of the day, it saves some money as well, and that’s what’s driving most businesses – it increases your profit. If you reduce the amount of energy that you’re using – energy is a direct operating cost of your business – it’s money that goes into the bottom line and turns into profit at the end of the year. That’s what’s driving a lot of these initiatives as well. So, return of investment is also important.
As we can see from the graphs here, energy costs are predicted to rise over the next few years. At the moment you’ve got non-industrial energy costs, which are probably running anywhere between 7 to maybe 11 pence per kilowatt hour. We can see industrial costs, as well. They’re all following this same pattern, but over the next 10 or 15 years, we expect that energy costs are going to go up by about 40-50%, depending on which stats you look at. The scary thing about that is the direct effect it will have on your business, because that’s going to be eating away at your profit. There’s an opportunity now to deal with that, and to actually look, at this point, at how you can reduce your energy usage and counteract some of this. If we just stay where we are at the moment, this is going to directly hit the profitability of the business moving forward. That’s not something that, in these tough economic times, we can all afford to do in our individual businesses.
In refrigeration terms, energy is a major proportion of your running costs. If you look at this graph here: when you buy a refrigeration plant, about 15% of the total life cycle costs of that refrigeration plant is the capital cost. That’s the bit that we always focus on – we want it cheap, we want the cheapest one that we can possibly get, focusing on the capital cost. But that’s a foolish approach, if you consider the fact that the ongoing maintenance and the operating energy cost of that equipment throughout its life cycle can be around about 85%. This morning, we’re going to talk about the energy side – that’s the bit I’m dealing with – and Andy’s going to be talking about the aftercare side in the second part of today’s presentations. So, why are we always focusing on this, when this is the bit that really hurts us and will hurt the profitability of the business moving forward? I’m going to focus on how we can get this part down and reduce the amount of energy that we’re using in our refrigeration systems.
A great starting point – and it seems an obvious one, but very few of us actually do it – is actually to start measuring. How many people have energy meters fitted? How many refrigeration plants run away, and they’re just part of the total energy usage of the site? The great rule is – if you can measure it, you can do something about it. You need to start measuring. These are relatively simple and easy and low cost to install. They’ll probably return on themselves within a twelve month time, in terms of the fact that you’ll start to focus on your energy. You’ll start to focus on how many kilowatt hours you’re using. You will know where the kilowatt hours are being used. And over time, you can start to address why that energy usage this month is higher than it was last month. Why is this year’s energy bill higher than it was the year before? And you can focus in on the things that are going wrong with the particular system that you’ve got and try to address them. At the same time, you can look at how your system is operating, and say to yourself “what can I do to try and improve that?” You can put measures in place and see the benefit. So, a great place to start – start measuring. For a few hundred pounds, you can have these fitted and you can start today.
In terms of energy efficiency: I’m going to cover four areas that affect how much energy your refrigeration system is using, look at those areas in detail, and give you some tips and ideas on how to look at improvement. I will also give you some data that we’ve got from work we’ve done, case study information, and some projects that are actually ongoing at the moment.
The first point that I’m going to cover is in terms of actually dealing with “where does all this heat and energy come from, where does the cooling load?” Why is it there, and how can we try and reduce that? Because the simplest way of actually making a plant more efficient and using less energy is to get rid of the heat to start with. If the heat’s not coming in, if the energy’s not needing to be removed, then the plant will run less. It might even switch itself off.
We will then look at the temperature in which it operates. In a refrigeration system, if you can bring the temperature at which you’re cooling up, then you can bring the temperature at which it’s rejecting the heat to the ambient down, and this improves the efficiency. We’ll then look at how the selection of components within that system affects the overall efficiency. And finally, we’ll look at how operating those pieces of equipment in different ways, particularly through variable speed drives, you can improve efficiency also.
Let’s start with the actual load for a refrigeration system. That’s made up of lots of different parts, and it’s lots of different things that affect it. Ambient temperature is one. If you’ve got a building – a warehouse – and it’s 35 degrees outside, and it’s -20 degrees inside, then you’ve got a temperature difference. And that’s driving energy into the building, which you then have to remove with your refrigeration system. It’s no different with air conditioning, but then you start to look at other areas. You can insulate your building and you can insulate pipes. Depending on how you insulate them will affect the amount of energy that’s flowing into the building that you have to remove through refrigeration.
Air ingress into areas, whether it be a warehouse or an office building, is an important part. Also moisture, products and the people that are in there – they are all adding heat. We’re all adding heat to this room now, which this air conditioning unit is trying to battle to remove as quickly as possible. Electrical load lighting is a prime example, and also a hidden one that people don’t think about. But when you’re operating at lower temperatures close to zero or below, you have defrost, and when you defrost you’re putting energy into the environment often to carry out that defrost process and then that has to be removed again by refrigeration.
So, if we look at ambient temperature. Ambient temperature varies throughout the year, and that has an effect on the building. These are the average daily temperatures in three parts of the UK. This will be important later on when we start to look at aspects like free cool. You can see that varies throughout the year, and if you can get your refrigeration plant to follow that profile – both in terms of its condensing temperatures, etc – you can ultimately improve your efficiency. At low ambient temperatures, you want it bringing the temperature at which your refrigeration system is expelling its heat into the environment to be following these lines here.
Insulation is a key way of preventing heat getting into a building or getting into pipes. Basically, what happens is that as your insulation gets thicker, the amount of heat that is flowing into a building is reduced. If you’ve got a typical freezer chamber and you add 50mm of insulation, you’ve got a heat gain of about 24w per metre squared. As you increase the thickness, the amount of heat gain that’s going in per metre squared of insulation decreases. It’s the same if you look at it in a chilled room, in a food factory, or even in an office environment. Because the temperature difference is far wider in the lower temperature environment, obviously you’ve got a greater effect by increasing the thickness. Then its optimization – how much thickness do you put in? Once you get to around 150mm, you’ve probably optimized it, because you can increase the thickness more and more but the benefit that you’re getting is less and less.
A big bane of mine and many an energy server is ingressive heat through doors. Whether this is loading docks, for example, in a distribution warehouse, but it could also be through leaving doors open in an office environment. Energy from the outside comes in. You spend all this energy trying to keep up a temperature environment and looking at things like BREEAM points and leakage in buildings, and then you find this happens. You’ve spent all your time making sure you’ve got a great door seal around this particular loading dock and you’ve got these great door seals around your doors in an office environment, and then somebody leaves them open. Therefore all of that, those great seals, has just gone straight out the window. And what you’ve got is an outside temperature, which is typically higher than the chamber you’re keeping cold, and that creates a pressure differential. The higher pressure outside drives the air in and that ultimately then has to be removed by the refrigeration system.
To put that into context – say you’ve got an ambient temperature of 32 degrees on a warm summer’s day. High humidity often comes with higher temperature, and you’re keeping a chamber at 2 degrees. For every one metre of air ingress, you’re bringing in about 100 kilowatts of energy – that’s 30 kettles. You might as well just bring 30 kettles in and get them boiling, that’s what you’re doing to your warehouse.
If you’ve got an efficient refrigeration system that's providing three kilowatts of cooling for every kilowatt of energy that you’re putting in, you’re using about 34 kilowatts of energy. So what does that mean? That equates to over £17,500 a year in additional running costs – because a door’s open. It’s criminal to allow that. When you wander around warehouses and offices, you see the effect of that increases if it's a lower temperature chamber. It increases by about 40%. If it’s an office chamber, it reduces by about that sort of amount. But even so, you’re still talking about big money. That’s money you can save just by shutting a door. If you often think that, “well these are damaged and we can’t afford to repair them”... you really can’t afford to repair them? Because that’s what it’s going to cost you if you really can’t afford to do that. So, as Larry Grayson used to say – “shut that door”. That’s a key thing to do, always keep the door closed.
Free cooling is a great option, particularly when you’re looking at warmer environments – offices and data centres in particular. We go back to our graph again, average temperatures throughout the year. In a data centre, for example: where you’ve got IT cooling, you might only need to provide the cooling fluid at a temperature of about maybe 12 or 14 degrees. There are opportunities where the ambient temperature drops. This is a mean temperature, but obviously the temperatures can be much lower than this, particularly in winter. You’ve got the opportunity to use the ambient temperature to your advantage and actually provide free cooling.
If we look at a small example here – here’s your refrigeration system. You’ve got your cooling fluid going in here at the bottom. It might be returning from your data centre at about maybe 18/20 degrees, and it’s being cooled in here by an evaporator. If the ambient temperature outside is much warmer than the fluid in here, you need to use your refrigeration. The refrigeration compressor takes the gas that’s being boiled in here, which is in turn cooling the fluid, and it compresses it and rejects it to the atmosphere. It needs to compress it to a higher temperature than what the atmosphere is in order to reject the heat.
If the temperature starts to decrease, such that the outdoor temperature is lower than the fluid temperature that we require, then we can use the laws of gravity. And because the temperature here is warmer than here, the gas will actually flow under gravity up, and you can switch your compressors off. Free cooling. And the same can be applied to air handling units where we’ve got lower ambient temperatures. We can divert fresh air in and provide cooling that way. This is typically used in a data centre environment, as I mentioned earlier on, where we’re not talking about a few tens of kilowatts – we can be talking megawatts. Data centres typically have megawatts of cooling loads. Megawatts in some data centres, we’re looking at either 15 or 20 megawatts. You think about the amount of energy that you can save just by switching all of your refrigeration plant off and using free cooling. At the moment, most data centres will run 365 days a year, 24 hours a day. Think how much energy you can save based on the graph we showed earlier on.
If we go to our 35 degree ambient really hot summer’s day, we’ve got all our refrigeration plant running flat out. We’ve got water coming back to the data centre at 18 degrees and going out to the data centre at 10 degrees. All of our plant is running. We’ve got a good efficiency, because we’ve got a good refrigeration system operating here. If we start to then bring that temperature down as the ambient temperature falls, as we come down to 20 degrees, what we see here is the efficiency of the refrigeration plant is improving because the refrigeration plant is acting on the fact that the ambient temperature’s lower. It is using that to its advantage to reject heat at a lower temperature so its energy efficiency increases. The real magic comes as we move further down the scale, because when we get to 8 degrees, the fluid coming in is at a much higher temperature than the ambient 8 degree environment. That then allows us to switch these compressors off, so we’ve automatically reduced our energy consumption by a third.
If we take this down another step, down to about 6 degrees, this second chiller which is in series with the first is now actually able to go into cooling. We’ve got two thirds of our energy at 6 degrees ambient for nothing, apart from running a few fans. And once we get down to the final step, which is about 5 degrees, all of our compressors are off. To put this into context: for these refrigeration systems, about 75-80% of the energy absorbed to do that cooling is through the compressor. By using ambient temperature, we can actually do all our cooling, and switch 80% of that energy off. It’s a massive way of reducing your energy bill. And this is applicable to anywhere where you’re using higher temperature secondary fluids throughout a building.
Moving on to electrical loads. We talked about lighting earlier on – it’s an obvious example, a lot of people are doing this now and it really came out of the work that was done in office environments and domestic environments. A lot more LED lighting is being used in warehousing, so any of you that do have warehouses, here is a great opportunity to reduce your energy bill. The refrigeration plant removes the energy that the lights produce, which are pouring into the store, and by switching to LED lights we can dramatically reduce that load. Lighting tends to be a constant load. By switching to LED lighting and reducing the energy that the lights take up by about 70%, we can get a benefit. But at a lower temperature, which is this example – here is an aisle within a cold store which typically uses seven 250 watt lights. They’re running 24/7. In a cold store, you can’t switch the lights off. Once these lights are on, if you switch them off they take about 15-20 minutes to warm up again. From a health and safety point of view, that’s a nightmare. It’s a continuous operation, over 15,000 kilowatts per year are being put into that store. And that means we’re probably using 80-10,000 kilowatt hours a year to remove that heat.
Moving to LEDs. Just keeping the same lighting layout, you can reduce the energy consumption to 48 watt lighting. It gives you the same amount of lighting and what you’ll notice is, it’s actually a lot clearer. The lighting is a lot crisper, and it’s far better for people that are operating within the store. With LED lighting, you can go to an intelligent lighting scheme, where if there is no movement in the aisle, the lights switch off. And with LED lighting, they can come on and off as much as you like. With 24/7 operation, you’re saving about 5% energy. Actually, if you’ve got an intelligent lighting scheme with the lights switching on and off, you can reduce the energy consumption by 85-90%. All that’s affecting is the lighting bill within the building itself, and it’s reducing the amount that is going onto your refrigeration system. And as I mentioned earlier, there is also improved visibility within the store.
So, we’ve looked at where the loads are coming from and how we can look at improving the efficiency of a plant. Let’s move on to the temperatures at which we operate. A refrigeration plant removes energy at one temperature and rejects it at another. If we can erase the temperature at which we’re providing that cooling for every degree that we improve, in a low temperature application for freezers, we’re going to improve around 5% on the compressor. If it’s a chiller environment, that can be as high as 4%, or for air conditioning that can be 2½ to 3%. How cold do we need to keep it? If we can raise that temperature, all the better.
Here is a case study for a warehouse. The client had a number of distribution warehouses, and they were looking at what the maximum temperature was that they could operate their freezers and chill chambers. For the freezer, they decided they could take it up to -20 degrees. It was previously operating at -25 degrees. For the chill temperatures, they took them up another couple of degrees as well. At the same time, we looked at methods of how we were measuring temperature. In a warehouse like this where you’ve got products all the way up the height of the building, it’s important that you maintain a relatively uniformed temperature level. So, we installed various probes around the store, and we were monitoring the temperature of those very seriously.
In other chambers, we had no racking. The ceiling was about half the height, but we only actually needed to cool to two metre levels. We put some temperature probes down at low level, up to two metres. We were not that worried about the temperature above that. Previously, we were measuring temperature at the height of the building, which would actually be the warmest part. Now we’re only interested in the lowest part, which meant that we could only raise our cooling temperature by about a degree or two.
We installed a temperature monitor system – quite a comprehensive system with about 40 or 50 points around the store – and that enables them to also prove temperature compliance through regulatory requirements. We re-calibrated and re-commissioned the refrigeration systems so that in the freezer, we were maintaining a uniform temperature at all heights, but in the chill chambers we were only looking to maintain the temperature that was required to keep the product at the low level of temperature it needed to be. Through that re-commissioning of the plant, we got some really beneficial energy savings. Through the re-commissioning and also through raising the chamber temperatures, what we were seeing across the five distribution warehouses was improvements of up to 21% in terms of the energy consumption. That’s a year on year comparison, so we’ve looked at 12 month periods, and we’ve looked at that month, 12 months on. There will be variations in ambient temperature, but even after taking that out, you can see that there was a benefit which was at least three quarters of what we’re seeing there. There are huge benefits by looking at what temperature you’re actually maintaining warehouses at.
The other benefit we got out of this as well is through the temperature monitoring. We’ve got some examples at the back where we actually got far better compliance with what you see here. All the green areas were within -/+1 of required temperatures within the chamber, so we were getting something like 98% compliance throughout that. It helped the client in terms of proving the reliability and the effectiveness of their cooling system within a warehouse.
We spoke a little bit about free cooling earlier on, but what temperatures do you need to provide chilled water? This is a data centre application using screw compressors. What we see here are various temperature lines for chilled water and the efficiency of the refrigeration system, the peak ambient temperature. At the lowest temperature of the chilled water, we get the minimum efficiency. This chiller’s around 2.6/2.7. If we actually raise the temperature of the chilled water up to around 16 degrees, what we’re seeing is that we can get an efficiency improvement of around about 20-30%. Furthermore, if we can actually reduce the condensing temperature of that refrigeration system as the year goes on and we get these changes in ambient temperature, we can improve efficiency quite markedly. We go from an efficiency of less than 3 to an efficiency approaching 6.
It’s key that we actually provide the cooling at the temperature we really do need, rather than what the standards are. In the standard conditions, everybody picks 12 and 6, but do you really need that water for a data centre? Can you raise it? Can you get free cooling like we saw earlier on? Because this has a massive effect on cost. As the ambient temperature varies, if the temperature of the ambient goes up, obviously it costs more to run. This is for a 200 kilowatt compressor. It is costing tens of thousands per year. If we can bring the temperature of the fluid up, that would save £10,000 a year in running costs. Okay, you might not be able to do that – but you might be able to bring it up and save a few thousand pounds a year.
We’ve looked at the cooling temperature at which we’re operating, and the same at the other end of the scale, the temperature at which we’re rejecting. We get a very similar effect here. If we can reduce the temperature that rejects heat by 1k, we can improve things by about 3% in frozen environments, and about 2.75% in chill environments. That would be for a typical evaporative type of application for a warehouse. If we look at air conditioning, where we’re air-cooled – we’re operating at a higher temperature because it’s air-cooled rather than evaporative. We’re using dry bulb rather than wet bulb temperature. We get a significant benefit on the air-cooled applications of nearly 3% for every 1 degree that we reduce the condensing temperature.
And how can we do that? Particularly when you’re looking at locations of condensers, you really need to think about where you’re putting these, because you want the most effective way of rejecting heat. Here are some ways of how not to do it: putting blocked walls on the face of condensers or restricting air-flow onto here means that you can’t get fresh air onto the condenser. You need a good air-flow getting onto the condenser, and ideally moving it as far away as possible from solid walls. Otherwise, you run the risk of air re-circulation.
For slanted buildings where we’ve got a roof coming down, if your condenser is below that on windy days, you’ve got a good chance that the air flows down the roof and blows the air back onto the condenser, and the condensing temperature then goes up. We’ve seen examples of condensing temperatures increasing by 5-10 degrees, just because of the location of the condensers. So, you want something with lots of fresh air, lots of areas where you can get cold air onto the condensers and then you’re not getting this re-circulation. It’s just plain daft, but we’ve seen that. If you’re blowing warm air at a wall, it’s just going to go round in circles. Face it in the other direction, it’s as simple as that.
The cleanliness of the condenser is key as well. They get blocked with leaves, they get blocked with dust, they get blocked with carrier bags... condensers are just hoovers. Keeping them clean is important, because over time they build up a resistance to temperature. The heat exchange and the efficiency drops. You should be keeping regular cleaning maintenance every so many months, just keeping a check on it. Somebody could even go by everyday just to make sure there are no plastic bags connected to it, etc.
Expansion valves are also important, particularly on smaller systems where you’ve got thermostatic expansion valves. Thermostatic expansion valves need a pressure differential across them to operate. So, what does that mean?
Well, the ambient temperature is varying throughout the year, but your thermostatic expansion valve is typically keeping the condensing pressure fixed, so you’re not getting any of its benefit at all. You’re just operating on a fixed differential in your refrigeration system, so you’re running it in the most inefficient way throughout the year. Moving to electronic expansion valves – what you can do is allow the system pressure to vary with the ambient temperature. All this space here between the red line and the blue line is energy that you’re saving. That can be fitted to relatively small, simple refrigeration systems and paid back within a very short period of time.
We now move on to the components within a refrigeration system, and we’ll break those down a little bit. Here’s a typical refrigeration system for a warehouse, where we’re providing refrigeration to some room coolers. In terms of the breakdown, we’ve got the main components in here – we’ve got compressors, a condenser, and room coolers with fans. If we look at the breakdown where the electricity is being used, we can see where to focus our efforts. 90% of the energy is being used in the compressor, so anything we can do to improve the energy efficiency of those compressors is good. We can deal with some of the auxiliary loads like the evaporators and the condenser fans, but this should be the focus of our efforts.
If we move to a secondary chiller, the picture is just slightly different. This time we’ve got a pump which we’re going to start to incorporate into the system, and this could be for any air-conditioning type of application in a data centre and the like. Now we’ve got 75% of the energy being used in the compressors, 15% being used in the fans, and 10% being used within the pumps. We’ve got a different dynamic here, but the compressor is still the major thing that we need to focus on. The same principles apply: getting the evaporating temperature and the cooling fluid temperature as high as possible. So, get your store temperatures high and get your fluid temperatures high.
Here is the graph that we showed earlier – here’s our screw compressor with its efficiency down here. By moving to a centrifugal compressor, if we just switch between these two loads here, what you see is we get a massive change in the efficiency. Previously we were looking at efficiencies that went from just around 3 degrees up to close to 6 degrees at low ambient conditions. By using a certain type of centrifugal compressor, what we can see is that we’re starting off with an efficiency that’s probably 10-15% higher and getting into the realms of 9 degrees. Equipment selection is important for the type of application, and this is specific for air-conditioning or data centre type of applications where you can see that there is a marked difference between these two crafts. If we start to look at what the energy benefits then are – and we’re talking about cost savings that are going on a 250 kilowatt compressor operating throughout the year in a data centre – you could be saving £20,000 a year in running costs, which is a huge benefit.
The reason for that is, typically with a screw compressor we’re operating, we have to maintain a differential for the oil circuit, etc. When working with the electronic expansion valves that we looked at before, which are typical on screw chillers – if we allow the head pressure of the condensing temperature to float throughout the year, and we use the benefits and the efficiencies of the centrifugal compressor, what we can see is that we can get our COPs far higher. As we start to move up this steep cliff, we are improving the efficiency of our refrigeration system. The compressor takes advantage of low ambient temperatures and reduction in load to try and get as high an efficiency as possible.
We’ve got something similar, our Indigochillers. We can provide some information on those later, but what that means over the life of the plant – and this is for a 1 megawatt chiller – over time, effectively you could be saving millions of pounds in running costs over a 20 year life cycle. This is a typical sort of data centre application. It might cost similar, or maybe a little bit more at the initital stage to install, and it will cost you more in terms of the chiller cost. But actually, from year one, you’re saving money. The costs of centrifugal are much lower, and we end up in the millions of pounds level, so you need to look at the life cycle cost.
In terms of operation, here’s an example of a brewery project we looked at. We took out an old reciprocating compressor and we replaced it with an inverter-driven reciprocating compressor., the reason being that the efficiency of the old compressor with its fixed capacity control – which was step capacity control – dropped off of part-load conditions. With a variable speed drive, we actually saw an improvement, up to a certain point, in efficiency as the speed of the compressor reduced. And this load, which was a brewery, was quite a variable load. We were getting the benefit of this varying speed with the varying load of the brewery to improve the efficiency of the overall system. Such that – pre-installation here – kilowatt hours each week were running in the area of around 140,000 kilowatt hours as an average for the week. Post installation, just by changing the compressor – because it’s a major consumer – we got down to below 100,000. We saved 40,000 kilowatt hours per week on the installation just by changing one component.
If we look at fans in the smaller components – it’s still important and still can give you a benefit – most fans work on an on/off operation. This is an evaporative condenser with two fans, it’s the same for an air-cooled condenser as well. You switch the fans on, you switch the fans off.
As we’re running the fans, we typically operate at a far higher speed and a far higher air volume than we actually need, but it’s a very simplistic and crude control. All this blue area is wasted energy, and that is something that we can overcome. We’ve also got quite an erratic effect on the head pressure of the system, and that – as the fans come on – is really having a sort of jagged effect on the control of the plant and the compressor which we’re condensing. By moving to a variable speed control, we can actually match the speed of the fans to the changing in the ambient temperature. We can vary the head pressure far more smoothly and still get the benefit of the changing in ambient temperature to improve the efficiency in the refrigeration system.
This has been installed in a number of warehouses across the UK to try and improve efficiency. Going from on/off control – which is the least efficient – to the variable speed control. The way that this works is that at 100% speed, the variable speed control actually uses about 3% more control energy than a fixed speed motor. As we drop the speed of the system, the power reduces far quicker than the speed does by using the power lure. At a speed of about 75%, we’re using just over 40% of the energy. As we drop that even further, at 50% speed we’re using about 12% energy. Fans are running throughout the year, and rather than having an on/off control, we can get a huge benefit by actually just keeping the fans running but dropping the speeds down. It is a far more efficient way of working.
Here is an example calculation that we did for a variable speed control product. We see a fixed speed operation throughout the year here. The fan’s speed has 100% at about 30% of the year. When we broke it down, it’s about 75% for about 12% of the year, and 50% for 88%. When we looked at a typical profile – this was something that we just worked on in terms of a guideline and a rule of thumb – by going to variable speed, we could reduce the amount of energy consumption by about 25%. We then took this to a client, and they said “we want you to guarantee your figures, and guarantee what you’re going to produce in terms of energy savings.” So, we said okay, that’s fine. We’re a little bit more conservative.
We were shown paybacks between about just over three years and just over five years across four different sites, and we were shown savings between £5-10,000 just depending on the size of the site. We’ve got measured data – the client had a system for looking at the amount of energy in the system which was being used month on month, and we applied a small amount of benefits in terms of these being evaporative condensers. We were saying that because we were no longer on on/off control, and we would get better performance etc.
Here in this graph, the red line is of projected energy consumption month by month, and the green blocks were what was actually achieved. You can see that there are far more areas of white here, which is where we’ve saved energy. Then the green is going over the red line. Their predictions of the red line were based upon year on year of energy consumption data from previous years, and ambient temperature. There is a correlation that went in there, and the middle section shows the ambient temperature variation over the period that the tests were done. This was over a three month period. The red blocks here show the energy that was saved. What we actually found over the period that we were monitoring was that our estimates for how much energy we saved was 30% lower than what we actually achieved. We were actually overachieving on the energy savings. The client was delighted, and the return of investment calculation worked. It meant that they were actually overachieving on their return of investment.
The key things that I want to leave you with today are: when improving efficiency, the first step is to get rid of any loads that aren’t necessary. Remove them, shut the doors, change the lighting... look at all those simple tips that you can do to actually eliminate loads within a building or within a space. The next thing is to get the temperatures that you’re cooling at as high as possible, and get your condensing temperatures as low as possible.
Look at the equipment that you’re using – is it the most efficient equipment that I can use for that application? More efficient equipment might cost you a little bit more, but over the life cycle, the benefits you can get – as you can see – were huge. It can be millions of pounds over a 28 year life cycle. And whatever you’ve got at the moment, look to optimise it. What things can I do to install that are going to give me a benefit, and give me a good return of investment?