So this is a Nibe ground source 17 kilowatt three phase heat pump with a 300 litre accumulator tank. That's the connections coming through from the external onto the internal manifold system. As Rory said outside, normally that manifold system would be positioned outside in a chamber, but for display and let us change controls and see the effect of having less ground collector, we brought it inside to play about with the flow rates and see what sort of effect it has on the machine. So as I say, you have the heat source, the heat pump here, just with a flow and return into the buffer tank and then a simple flow and return system to the under floor manifolds. One of them is up above the door there and the other is in the cut so there's two distribution systems that are controlled off two individual thermostats in the room, shutting down the different circuits. So at the moment, that's it running, and it just started there and ran. I don't think anybody would have been able to tell me that was running.
The loudest thing that is actually there is the meter thing that is registering the flow rate for the heat meter system. So what we are actually measuring is the power going into this unit and we are measuring the heat output. We are bringing the water in at 11 degrees, which is really quite, that's really warm and it's going back out at 5.8. So we are extracting 6 degrees from the ground and we are producing a flow temperature of 46 degrees, with a return temperature of 36. So we are adding 10 degrees into this heat, into this buffer tank. So we're taking that heat energy, what we are actually doing if we go to this one, we are actually taking that 6 degrees, putting it into the refrigerator, putting it into the refrigerant and then when we compress the refrigerant we are raising the gas temperature up to 76 degrees. So we are turning 6 degrees into 76 degrees and we are doing that by compressing the gas, the refrigerant gas and that's why we get that efficiency. We are taking one level of heat and amplifying it.
So, this one as I say it is working very well at the moment. What we will get over time, as we start to extract that energy, as Tim was saying, we will cool the ground down, the boreholes will cool down slightly. But hopefully if we can maintain 6 or 7 degrees coming in, if we've got a good design then there's no reason, we should still achieve cop's in excess of 5. There's no reason why we shouldn't get that. So it's quite nice to see, how we can get a setup in here and see everything in real time - I'm not making anything up, the figures are here. At the moment there's no hot water in demand on this circuit but normally it would be piped off to a high efficiency cylinder. We have to make sure we can exchange the heat away from the heat pump.
The vessel is so large through 100 litres to absorb because if we have a heating load as we heat the building and zones actually start to close down, the heating load actually changes and if we had it going straight without the buffer tank it could affect the flow rate system.
Question - do you necessarily need a 300 litre vessel for this size system?
The answer is no, if the system is well designed and the control system, if you have open circuits, but in something like an office block where you have different requirements for different areas, there is going to be changing conditions, and to avoid there being any effect, so this buffers it, it smoothes out.
Question - I thought it was always, well my understanding of it, I thought it was 20 litres per Kilowatt?
It is. That's Nibe's guidelines to it. Yeah. I mean 300, we've got a 17 Kilowatt, but we know we have about four or five circuits that haven't got any controls on it so we can use that volume in the uncontrolled circuits. Plus the volume in here to get your 340 litres, I mean you're not really that far away anyway. Yes you could say that's undersized but its not, and in fact when Nebe first came into the UK, we were encouraged, with the control system, the way this control system thinks, there shouldn't be a need for this tank at all but in the UK, because of the fluctuations in temperature we get, because we can go from 0 degrees to +14, or +8 or 9 in the space of 6 or 8 hours.
Question: Is that because of the compressor?
Yeah. I mean this is a fixed speed compressor, which means that the output is always 17 Kilowatts. Some other manufacturers may use inverter driven compressors which means that as the system closes down and you're not using 17 Kilowatts the compressor slows down. This doesn't do this, this is a fixed speed but what they have is a very sophisticated control system to allow it to try and smooth out these peaks and troughs and just keep it evenly turning over, but it's a kind of safety net. And we have found in this country, either with the reluctance to remove controls from systems and also if you think about it as in not a commercial sense but a domestic sense we tend to have compartments in places. We tend to have doors in most rooms, whereas the Scandinavian way is to have doors in the bedrooms and everything open plan which means if you have everything open plan there isn't much point having control systems all over the house.
If you've got an area like this there's no point having a stat over there and a stat over here and expecting that to give you any sort of reasonable control. Whereas in the UK we tend to have dining room closed, lounge closed. And if you have got that system, the need for controls is more relevant. So it brings us back to, we would love to have no controls on the system and let this system, the sophisticated control system do its job and yet we constantly come up against systems where we've got 10 or 15 different zones being controlled by thermostats. People will go round and turn down about 10 stats and ignore this because it looks complicated. It's trying to get that through to people. If you turned down all the stats and this machine is doing something different, you're creating an imbalance. It's not an efficient way to run it. But that's ok for me to say, it is quite technical to understand the system. But it is and it isn't. If you invest the time to set it up, it should be a leave it alone as you can set it up to your requirements and then you can walk away. That's the other thing; everybody's different and in the offices one person will come in and turn the stat down and another person will turn the stat up. That's the reason for this - to allow that flexibility.