Dr. Rob Lamb - Enhancing The Efficiency of New and Existing Cooling Systems
This is a video recording of Rob Lamb's presentation at the Star Refrigeration Roadshow 2013 in Glasgow, discussing how you can make your plant more energy efficient with improvements such as free cooling and LED lighting.
One of the points that David did point 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’s now starting to level out, and I’m not quite sure what that is. Despite the fact that – as David pointed out in one of his CO2 graphs earlier on – the CO2 level now is at record proportions and way out there. Temperatures seem to have been stabilising and scientists are saying that that is because heat is starting to go into the sea, and the sea is starting to warm up and 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 – 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 that we’re chucking into the atmosphere and the amount of CO2 that we’re pouring into the atmosphere, which is then potentially causing this heating problem. So, there’s a good environmental reason for looking at energy efficiency, and there’s 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 – if you can get that down, 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 seven to maybe eleven 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 what you look at, which stats that you look at. The scary thing about that is the direct effect on your business, because that’s going to be eating away at your profit. So there’s an opportunity now to deal with that, and to actually look, at this point, of 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 – that 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, very simple, nicely coloured – when you buy a refrigeration plant, about 15% of the costs, 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 rest of this here in the red and the blue area, is the ongoing maintenance and the operating energy cost of that equipment throughout its life cycle, which 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.
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 know where the kilowatt hours are being used. And over time, you can start to address – why is that energy usage this month 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, and hone in, on the things that are going wrong with the particular system that you’ve got and try and 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 you can 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 efficiency, I’m going to cover four areas that affect how much energy your refrigeration system is using, look at those areas in detail, give you some tips and ideas on how to look at improvement, and give you some data that we’ve got from work that 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, 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’ll then look at the temperature in which it operates, because 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, you improve 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.
So, 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 35o outside, and it’s -20o inside, 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, you can insulate pipes. Depending on how you insulate them will affect the amount of energy that’s flowing into the building you have to remove through refrigeration.
Air ingress into areas, whether it be a warehouse or whether it be an office building, is an important part, and also moisture, products and people that are in there – they’re are 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 affect on the building. These are average daily temperatures at 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. Because what you really want it doing is at low ambient temperatures here, you want it bringing the temperature at which your refrigeration system is expelling its heat into the environment, you want to be following these lines here. We’ll cover that a little bit later on.
If you look at insulation, insulation is a key way of preventing heat getting into a building or getting into pipes. Basically, what happens is that your insulation gets thicker, the amount of heat that is flowing into a building is reduced. Such that if you’ve got a typical freezer chamber, if you add 50mms of insulation, you’ve got a heat gain of about 24 watts per m2. As you increase the thickness, the amount of heat gain that’s going in per m2 of insulation decreases. It’s the same if you look at in a chilled room, in a food factory, or even 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 about 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, I’ve spent wandering around a temperature warehouse, is ingressive heat through doors. Whether this is loading docks, for example, in a distribution warehouse, but it could 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 look at all these 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 then by the refrigeration system. To put that into context – if you’ve got an ambient temperature of 32oC on a warm summer’s day – it’s a difficult one here, I know that, but it does get to 32o. High humidity, which often comes with higher temperature and you’re keeping a chamber at 2o, for every one metre of air ingress you’re bringing about 100kW 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, which is providing 3kW of cooling for every kW of energy that you’re putting in, you’re using around about 34kW 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, you wander around offices and you see that the effect of that increases if its 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. And you often find that, “well these are damaged and we can’t afford to repair them”, well 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 cool is a great option, particularly when you’re looking at warmer environments – offices, 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 14o. Now, there are opportunities where the ambient temperature drops and this 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. So, 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, 20o 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.
But, if our temperature on the top left there starts to decrease, such that the outdoor temperature here is lower than the fluid temperature that we require here, 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 and 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 20mW. You think about the amount of energy you can save by switching all your refrigeration plant off and using free cooling. At the moment, most data centres will run on six twelve water, and they’ll 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 look at a bit more of this animation, if we go to our 35o 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 18o, going out to the data centre at 10o – 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, concentrate on the top left there as we come down to 20oC, 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 and it’s using that to its advantage to reject its heat at a lower temperature so its efficiency increases. The real magic comes as we move further down the scale, because when we get to 8oC, this fluid coming in here is at a much higher temperature than the ambient 8oC environment. That 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, and we take that down to about 6oC, now this second chiller which is in series with the first, is actually able to go into thermos life and cooling. So, we’ve got two thirds of our energy at 6oC ambient for nothing. Apart from running a few fans. And once we get down to the final step, which is about 5oC, 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 that 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.
Going 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’s a great opportunity to reduce your energy bill because 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 that energy that the lights take by about 70%, we can get a benefit. But at a lower temperature, which is this example – here’s an aisle within a cold store, which typically uses seven 250w lights, they’re running 24/7 and in a cold store, you can’t switch the lights off. These lights, once they’re 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 15,000kW per year are being put into that store. And that means we’re probably using, with a reasonable efficiency of maybe one and a half, two to one, you’re probably using 80-10,000kW hours a year to remove that heat.
Moving to LEDs. Just keeping the same lighting layout, you can reduce the energy consumption to 48w 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 more crisper, and it’s far better for people that are operating within the store. Now, with the LED lighting, you can go to an intelligent lighting scheme, where if there’s no movement in the aisle, the lights switch off. And with LED lighting, they can come on and off as much as you like. So, an intelligent lighting scheme. With 24/7 operation, you’re saving about 5% energy, but actually if you’ve got an intelligent lighting scheme which is the lights on and off, you can reduce the energy consumption by 85-90%. And all that’s affecting 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, 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, a low temperature application for freezers, we’re going to improve that 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%. What we’re trying to do is actually – how cold do we need to keep it? If we can raise that temperature, all the better.
Here’s a case study for a warehouse and we’re going to go onto a data centre after that as well. For a warehouse here, the client had a number of distribution warehouses and they were looking at what was the maximum temperature they could operate their freezers and chill chambers. They decided on the freezer, they could take it up to -20o, previously operating at -25o. The chill temperatures, they took them up another couple of degrees as well. At the same time, we looked at methods of where we were measuring temperature. In a warehouse like this where it’s racked, you’ve got products all the way up the height of the building, and 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.
But in other chambers, we have no racking. The ceiling was about half the height, but we only actually needed to cool to two metre levels. So, we put some temperature probes, now, down at low level up to two metres – but actually, the temperature above that, we’re not really that worried about. 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. That means 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 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 low level of the temperature it needed to be. But through that re-commissioning of the plant, we got some really beneficial energy savings. Through that re-commissioning, and also 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 taking that out, you can see that there was a benefit which was at least three quarters of what we’re seeing there. So, 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, 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.
If we move on to chillers – we spoke a little bit about free cooling earlier on – but driving up chiller temperatures, what temperatures you need to provide chilled water. This is a data centre application using screw compressors, and what we see here are various temperature lines for chilled water and the efficiency of the refrigeration system. The peak ambient temperature, and at the lowest temperature of the chilled water out at 6, we get the minimum efficiency. This chiller’s around 2.6/2.7. If we actually raise that temperature of the chilled water up to around 16o, what we’re seeing is 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. So, 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 12o and 6o but do you really need 12o/6o 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’s costing more to run – this is for a 200kW compressor. This is costing tens of thousands per year. If we can bring that temperature of the fluid up – here I have an example of it raising by 10o – 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, same at the other end of the scale, the temperature which we’re rejecting. We get a very similar effect here, in that – if we can reduce the temperature that rejects heat by 1k, we 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. Because 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 1o that we reduce the condensing temperature.
And how can we do that? Well, 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’s some ways of not to do it. Putting blocked walls on the face of condensers or restricted air-flow onto here means that you can’t get fresh air onto the condenser and throwing it out, 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.
Slanted buildings, we’ve got a roof coming down, if your condenser’s 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 goes up. We’ve seen examples on these two of condensing temperatures increasing by 5-10o, just because of the location of the condensers. So, you want something with lots of fresh air, lots of area where you can get cold air onto the condensers and you’re not getting this re-circulation. That’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. Everybody quotes – “perfect clean fins for the air condensers, whatever time they get dirty”. They get blocked with leaves, they get blocked with dust, they get blocked with carrier bags... condensers are just hoovers. So, keeping them clean is important, because over time they build up a resistance to temperature. The heat exchange and the efficiency drops. Keeping regular cleaning maintenance every so many months, keeping a check on it – if somebody even goes by everyday just to make sure there’s not plastic bags connected to it, etc.
Expansion valves are 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, as we saw, 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, like this one here – 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 with its fans, and room coolers with its fans. If we look at the breakdown where the electricity is being used, we can see where to focus our efforts, because 90% of the energy is being used in the compressor, so anything we can do to improve the efficiency of those compressors is good. We can deal with some of the auxiliary loads like the evaporators and the condenser fans but here 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 here, 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, we’ve got 15% being used in the fans, and 10% being used within the pumps. We’ve got a different dynamic here – the compressor is still the major thing that we need to focus on, and that’s what we’ll look at in the coming slides. The same principles apply, getting the evaporating temperature and the cooling fluid temperature as high as possible – so, get your store temperatures high, get your fluid temperatures high.
Here’s 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 3o, up to close to 6o 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 9o. 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 there’s a marked difference between these two crafts. And if we start to look at what the energy benefits then are – we’re talking about cost savings that are going on a 250kW 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 electronic expansion valves, which 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 in this top corner. We can’t get anywhere near it on this side here. As we start to move up this steep cliff here, 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, which are shown at the back there. We can provide some information on those later. But what that means over the life of the plant – and this is for a 1mW chiller – what we can see is, 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 initial stage to install, 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’re 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 that 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 old compressor with its fixed capacity control – which was step capacity control – its efficiency 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. So, 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 – kW hours each week were running in the area of around 140,000kW 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 100,000kW, so we saved 40,000kW 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. Over time – if the ambient temperature changes – we have a step. Switching the fan on, switching the next fan on.
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 it’s 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 – it’s 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 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, which as you see, 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. Now, 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’s a far more efficient way of working.
Here’s an example calculation that we did for a variable speed control product, and we see here a fixed speed operation throughout the year. 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, 50% for 18%. 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 – and 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, 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. But 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 were evaporative condensers. We were saying that because we were no longer on on/off control, we would get better performance and out of belt etc.
What we’re looking at 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 there’s far more areas of white here, which is where we’ve saved energy. Then, the green going over the red line. Their predictions of red line were based upon year on year of energy consumption data from previous years, and ambient temperature. There’s 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. So, there’s a few tips in terms of ideas for installation of equipment.
The key things that I want to leave you with today are that in 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. Next thing is to get the temperatures that you’re cooling at as high as possible, 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. They 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?