For efficiency, there are lots of things we can do. We can locate the condenser correctly, We can use water resistant cooling for the condensers, We can use low TD condensers, We can use electronic expansion valves and we can make sure the solenoid valve is in the right position.
We can ensure that insulation is well done, we can manage air infiltration into our rooms and we can recover heat and offset gas use or electric heating elsewhere.
So let’s get into it.
1. Condenser Location
Condensers as- I’ll take you back to that little diagram I showed you right at the beginning-condensers need air to cool. They need lots of air. If they don’t have air, the temperature will go up, and your refrigeration system will use more power.
So condensing units need good cooling air. Do not fit them into basements or enclosed spaces. I always pause when I say that because it’s kind of obvious that you shouldn’t be doing this.
So it’s very common, poor airflow will cause the high condensing temperatures or cause the air to be recirculated, and that gives you high power consumption and potentially even a failure of the compressor.
So what am I talking about? If you look at the picture
that is a poor little condensing unit in an enclosed space. It’s like a concrete alcove or bricked alcove. I looked at that unit a bit closer. We’ll get to that. Here is an example of two groups of condensing units.
And you see the two condensing units
on the right hand side, which are mounted on the roof. Which do you think will be running more efficiently?
Now, I know you can’t answer back, but, of course, the ones on the right hand side would be running better.
So and why?
And I’ll show you a good example. This is what you should not be doing.
So left top, that is actually a little cool room for I think it was a fishmonger, and that condensing unit in the middle was located on top of the cool room behind that sliding door, which was put in place because it was a noisy unit.
So when I went to inspect it, and I opened the sliding door, it was like 50 degrees air coming out there. And of course, the reason why I went
there is because the system wasn’t working well, was it?
But the picture on the right was actually a apartment building, It’s a really good example of what an architect can do to refrigeration because these units were not allowed to be outside. So he had all the air conditioning and it’s on the left and all the refrigeration units on the right in the car park basement.
And that space in the middle is where a car is actually parked. So what you have there is all the air trying to cool the condensing units is being blown at the car and recirculated within that space. So these units will have a very hard time to operate, especially in summer, and whoever parks their car there, they will have a very hot car.
So that’s how not to do that. But just to show the impact that this has on energy use, I’ve done a few measurements using my trusty infrared gun again.
So what I’ve measured there on this picture–
you can see that someone was helping me on the left holding a air on temperature sensor. So that’s the air within that space. So this was a small condensing unit in a big market hall, so it had plenty of air. And you can see the air on temperature was 19 degrees.
OK, not too warm.
And then I measured the point where the liquid comes out of the condenser. So that’s kind of the condensing temperature. You could call it that. I measured that with my little gun, and you can see that was 26 degrees.
So the difference between air temperature and condensing temperature was about seven degrees. That’s really good. Like any system that’s running well, seven degrees is a good TD, temperature difference, where the air coming through the brick wall was 22 degrees, as shown on the left picture.
But by the time the air got to the condenser, it was now ready at 30 degrees, and the liquid coming out of the condenser was 43.
So what we had here was all the way from 22 to 43. We had 21 degrees Delta T. As opposed to seven, the previous one, this one was a 21. So if you compare the two, 14 degrees higher.
Remember the rule I said?
Two to three degrees per 2 to 3% per degrees, That would give you something like 30 to 45% excess energy use for this unit as it was running there simply because of the location of the unit
It wasn’t well ventilated, and it was rather dirty as well. And that was that unit that I showed you initially. So simply because of where it was located, that system was being permanently penalized and using 20% to 30% more power.
Here, we have two somewhat larger condensing units
The one on the left was mounted next to the cool room wall, and the one on the right was mounted facing outwards. You can see the trees in the background. Again, the question to you, which one runs better?
Well, you don’t need to be a genius to work out that the one on the right hand side is going to work a lot better because it gets the free air from the outside. One on on the left was about the width of my hand away from the wall. So you can imagine the difficulty that the air had getting around the condenser and the likelihood of that air then recirculating.
There is a rule out there which says at least half a meter away from a wall or at least half the width of the condenser away from a wall. And very often, these rules are not met. Maybe the owner was saying, no, no I need the space. Back it up against the wall. I don’t need it that far away. But again, you’re paying a permanent penalty in terms of energy consumption if you do that.
So give your units enough air. So then, roof mounted is great. Shaded is great. Don’t let them look into the west afternoon sun. Well-ventilated, no recirculation, and that will save you energy and also peak demand on those hot days.
That’s when you want to get the energy down because that’s the network costs that you pay as well.
So good airflow saves you throughout the year, and it saves you especially on those hot days. That’s the one thing I keep carrying on. Here’s an example, this is a brand new install and there we go.
This was a large room with a cool room inside, and they installed the condensing unit on top of the room. And the room was completely enclosed. So not only was the condensing unit inside the hot space, but so was the cool room itself.
So the cool room was sitting there with 40 degrees air around it trying to keep itself cool, so not a very good situation. So I see that all the time, even on brand new installs, and it’s often not the refrigeration technician’s fault.
It’s often that refrigeration is an afterthought. They think of everything except the refrigeration. This was in fact a brand new very notable building, and they just forgot to plan for location for the condensing unit.
So they just take it inside where nobody sees it. Here is one way to solve the problem, where you have a unit ducted it to the outside. That can work. You need to allow for the pressure drop in the duct, but if it’s properly designed, you can have the unit inside the basement so it doesn’t annoy anybody.
But even in this case, it actually serves as ventilation for the car park area as well.
2. Water-assisted Cooling For Condenser
Air cooling is the most common way of doing condensing in commercial refrigeration. Water-assisted saves energy quickly, and you can get 30% to 40% power at peak, power savings at peak.
How do we do that?
The cooling tower is the obvious solution, and sometimes this works. I often see large buildings where there is a cooling tower already for the air conditioning, and then they put an air cooled condensing unit in.
It’s kind of sad because you could have just tapped into the cooling water and had 30%, 40% energy reduction. So sometimes, one just has to look at what’s available.
If there already is water cooling available, use it. Don’t put air cooling in that same building. I referred to earlier had exactly that. They had water cooled systems, and, bang, they put the air cooled systems next to the water cooled system.
Often on a hotel, for example, the refrigeration is like 1% of 10% of the cooling capacity of the hotel. Most of it is air conditioning, It would make no difference to add it in. I’m not suggesting that you put water cooled condensers on your butcher shop.