00:00:02.000 [Applause] 00:00:04.30000:00:04.310 hey there guys pulled here from the 00:00:06.49900:00:06.509 engineering mindset calm in this video 00:00:09.02000:00:09.030 we're going to be looking at the cooling 00:00:10.82000:00:10.830 coils in an HVAC system to see what they 00:00:14.18000:00:14.190 do how they work and how to ensure they 00:00:17.12000:00:17.130 are operating efficiently and towards 00:00:19.49000:00:19.500 the end of the video we're going to look 00:00:20.57000:00:20.580 at some calculations for these also so 00:00:23.68900:00:23.699 cooling coils are really common 00:00:25.66000:00:25.670 component in HVAC systems and they 00:00:28.97000:00:28.980 usually come in two forms the first one 00:00:31.33900:00:31.349 being they are refrigerant they are fed 00:00:33.26000:00:33.270 refrigerant directly from an AC unit as 00:00:36.81900:00:36.829 you can see here so we've got the AC 00:00:40.04000:00:40.050 unit outside and this is just piped 00:00:41.75000:00:41.760 straight to the DX unit within the ahu 00:00:46.31000:00:46.320 or the fan coil unit now you can always 00:00:50.45000:00:50.460 tell if the cooling coil is a 00:00:52.45900:00:52.469 refrigerant based and that's because 00:00:54.02000:00:54.030 obviously it's got the expansion valves 00:00:56.38900:00:56.399 here and they're usually directly 00:00:58.13000:00:58.140 outside the coil and then you've also 00:01:01.84900:01:01.859 got the this is this photo here is from 00:01:05.71900:01:05.729 the inside of this coil and you can see 00:01:07.96900:01:07.979 that splitting away there and feeding 00:01:10.16000:01:10.170 off into multiple smaller tubes and off 00:01:13.34000:01:13.350 into the cooling coil now this type of 00:01:16.78900:01:16.799 cooling coil is controlled by there's a 00:01:19.78900:01:19.799 capillary tube just inside underneath 00:01:22.19000:01:22.200 this legging here and the tube rides up 00:01:24.64900:01:24.659 and then comes through this through this 00:01:27.28900:01:27.299 tube here and down low to the diaphragm 00:01:29.45000:01:29.460 of the expansion valve so that controls 00:01:32.92900:01:32.939 the refrigerant through them the meter 00:01:35.09000:01:35.100 device there if you haven't already done 00:01:37.81900:01:37.829 so I'd highly recommend you check out 00:01:39.83000:01:39.840 our children video where we cover this 00:01:43.58000:01:43.590 exact type of expansion valve and you 00:01:46.31000:01:46.320 should see your link just above you now 00:01:48.19000:01:48.200 now the other form of cooling coil 00:01:50.48000:01:50.490 you're going to get is the chilled water 00:01:51.83000:01:51.840 cooling coil and this is usually for an 00:01:54.53000:01:54.540 equal economical point of view whereas 00:01:57.64900:01:57.659 if you've got multiple 8h use or fan 00:02:00.13900:02:00.149 coil units or you 00:02:02.21000:02:02.220 a lot of cooling demand on the building 00:02:04.69000:02:04.700 then it's probably going to be more 00:02:06.92000:02:06.930 economical to have it from a centralized 00:02:09.17000:02:09.180 system rather than a localized direct 00:02:12.38000:02:12.390 expansion unit so this setup is more 00:02:15.59000:02:15.600 common in very large buildings 00:02:17.92000:02:17.930 whereas this setup it's much more common 00:02:20.99000:02:21.000 in places like shops or small sites and 00:02:25.19000:02:25.200 buildings so if the cooling coil is fed 00:02:27.80000:02:27.810 by chilled water then it's going to look 00:02:29.54000:02:29.550 to link a bit like this so the chilled 00:02:32.00000:02:32.010 water flows in through the bottom and 00:02:33.76000:02:33.770 flows through these passages here until 00:02:38.03000:02:38.040 it makes its way to the top and then 00:02:39.80000:02:39.810 exits back to the chiller and according 00:02:42.71000:02:42.720 capacity for these types of cooling coil 00:02:45.35000:02:45.360 they're just controlled by usually a 00:02:48.08000:02:48.090 motorized valve or it could be manual 00:02:49.88000:02:49.890 but certainly if you've got a BMS then 00:02:52.13000:02:52.140 it will be from a motorized valve and 00:02:54.47000:02:54.480 that just restricts some of the flow 00:02:56.72000:02:56.730 going into it to meet the set point 00:02:58.73000:02:58.740 whichever you've got for your low 00:03:00.92000:03:00.930 temperature or off coil temperature now 00:03:04.49000:03:04.500 there's some steps you can take to make 00:03:05.81000:03:05.820 sure that your cooling core is operating 00:03:09.08000:03:09.090 as efficiently as possible 00:03:10.91000:03:10.920 and the first step is to ensure that the 00:03:14.29000:03:14.300 the fins are cleaned regularly - all 00:03:19.55000:03:19.560 these little sheets of metal that run in 00:03:22.16000:03:22.170 between all the tubes they're known as 00:03:24.32000:03:24.330 the fins and because the warm air that 00:03:27.29000:03:27.300 comes in from the outside 00:03:29.42000:03:29.430 usually condenses on the cooling coils 00:03:31.99000:03:32.000 the surface of these can often be very 00:03:34.94000:03:34.950 moist and any dirt or dust that has not 00:03:39.28900:03:39.299 been captured by the filters will 00:03:41.72000:03:41.730 usually end up sticking to this and all 00:03:44.21000:03:44.220 that dirt it really just adds a layer of 00:03:46.40000:03:46.410 insulation and stops the heat transfer 00:03:49.07000:03:49.080 or the thermal energy transfer out of 00:03:52.31000:03:52.320 these these tubes and into the fins so 00:03:55.91000:03:55.920 the fins are there so that the chilled 00:03:58.61000:03:58.620 water is passing through these tubes and 00:04:00.32000:04:00.330 the fins just extract some of that cold 00:04:03.25900:04:03.269 thermal energy out of there pulling out 00:04:06.97900:04:06.989 into the air flow so the air passes 00:04:09.53000:04:09.540 through the gaps in between and the fins 00:04:13.61000:04:13.620 just extract some of that firmly 00:04:15.60000:04:15.610 gee out and spread it across giving it 00:04:17.61000:04:17.620 more chance for the air to take it away 00:04:19.78900:04:19.799 so the more dust that covers these fins 00:04:22.79000:04:22.800 the less chance the air has got to 00:04:25.86000:04:25.870 actually come in contact with the cold 00:04:27.48000:04:27.490 surface of the thin and take some of 00:04:30.60000:04:30.610 that thermal energy away or transfer its 00:04:33.99000:04:34.000 thermal energy back into the chilled 00:04:36.45000:04:36.460 water another very common issue with 00:04:39.78000:04:39.790 cooling coils is that the thins are very 00:04:42.63000:04:42.640 delicate so any knock you know if you're 00:04:45.48000:04:45.490 in there doing maintenance or anything 00:04:46.94000:04:46.950 there's a high chance you're going to 00:04:48.78000:04:48.790 knock these and that is going to damage 00:04:50.58000:04:50.590 the fins like you can see in the photo 00:04:52.86000:04:52.870 just here so what's happened here is 00:04:55.11000:04:55.120 someone's obviously knocked into this 00:04:57.42000:04:57.430 cooling coil and that's actually closed 00:04:59.82000:04:59.830 the fin so it's pushed and shut so no 00:05:02.40000:05:02.410 air can actually pass through there and 00:05:04.08000:05:04.090 that means that no heat transfer will 00:05:06.39000:05:06.400 occur 00:05:06.98000:05:06.990 Frias obviously the the air would 00:05:09.60000:05:09.610 normally pass through these gaps in 00:05:11.19000:05:11.200 between the fins but here it's been 00:05:13.38000:05:13.390 sealed seen it's been very careful when 00:05:16.35000:05:16.360 working around these if you have got 00:05:19.02000:05:19.030 some damaged fins and it's very easy to 00:05:21.18000:05:21.190 repair you can actually buy one of these 00:05:23.51000:05:23.520 condenser fin combs and they look a bit 00:05:25.98000:05:25.990 like this and they're very cheap they're 00:05:27.96000:05:27.970 around ten pounds ten dollars to buy and 00:05:30.96000:05:30.970 you just you find the right size fin 00:05:34.29000:05:34.300 fittings that you've got and then you 00:05:36.36000:05:36.370 just put it in like a comb and you push 00:05:38.94000:05:38.950 against that up and down a few times and 00:05:42.81000:05:42.820 that will actually straighten out all 00:05:44.52000:05:44.530 the fins back to new now I've left some 00:05:48.39000:05:48.400 links in the description just for where 00:05:50.85000:05:50.860 you can buy these from they're a very 00:05:53.67000:05:53.680 useful tool I really recommend any HVAC 00:05:57.33000:05:57.340 engineer that have one of these so if 00:06:00.06000:06:00.070 you just scroll down and hit the show 00:06:01.89000:06:01.900 more button and you can find those 00:06:03.60000:06:03.610 things below another important step for 00:06:06.03000:06:06.040 your cooling coils if they are chilled 00:06:08.64000:06:08.650 water fed then you should check that the 00:06:13.07000:06:13.080 cooling coils in your building are being 00:06:16.59000:06:16.600 fed chilled water and the water should 00:06:18.00000:06:18.010 be entering through the bottom and then 00:06:21.03000:06:21.040 rising up through that going against 00:06:23.25000:06:23.260 gravity which gives it more chance 00:06:25.20000:06:25.210 through turbulator become turbulent in 00:06:27.57000:06:27.580 there and give up 00:06:28.77000:06:28.780 with that thermal energy and then make 00:06:31.08000:06:31.090 its way out at the top if it's been 00:06:33.33000:06:33.340 piped incorrectly so the chilled water 00:06:34.98000:06:34.990 is entering through the top and leaving 00:06:37.44000:06:37.450 through the bottom if you were supply / 00:06:39.57000:06:39.580 and the other way the correct way then 00:06:41.70000:06:41.710 you're probably going to see about five 00:06:43.40900:06:43.419 anywhere between five and fifteen 00:06:45.12000:06:45.130 percent increase in effectiveness from 00:06:47.37000:06:47.380 that but if you do find one on your site 00:06:49.47000:06:49.480 please first check with your 00:06:50.70000:06:50.710 manufacturer to make sure that it has 00:06:52.71000:06:52.720 been fully designed for that operation 00:06:55.12900:06:55.139 another check you should have a look at 00:06:57.60000:06:57.610 on your site is if the the inlet for the 00:07:00.78000:07:00.790 chilled water should always be on the 00:07:02.52000:07:02.530 right hand side the furthest part away 00:07:04.80000:07:04.810 from the direction of flow so if your 00:07:08.01000:07:08.020 cooling coil is the other way around 00:07:09.53000:07:09.540 then it's actually back to front so if 00:07:11.76000:07:11.770 the if the inlet is on the face closest 00:07:14.94000:07:14.950 to the direction of airflow then this 00:07:17.25000:07:17.260 has been installed incorrectly also 00:07:19.21900:07:19.229 unless again the manufacturer has 00:07:21.36000:07:21.370 specifically designed it for that 00:07:23.10000:07:23.110 purpose so please check with them okay 00:07:25.89000:07:25.900 so let's have a look at some some basic 00:07:27.99000:07:28.000 cooling coil calculations so here we've 00:07:30.78000:07:30.790 got some sort of cooling device being 00:07:32.37000:07:32.380 either a fan coil unit or an a hate you 00:07:35.30000:07:35.310 essentially performing the same task but 00:07:37.77000:07:37.780 on a larger scale for an ahu and we know 00:07:41.07000:07:41.080 that this fan here is pulling in air at 00:07:44.21900:07:44.229 a volume flow rate of two meters cube 00:07:47.90900:07:47.919 per second we're going to temperature 00:07:50.01000:07:50.020 probe here and we can measure that that 00:07:52.40900:07:52.419 air coming in is coming in at a 00:07:54.36000:07:54.370 temperature of 30 degrees Celsius and 00:07:56.46000:07:56.470 from the BMS or maybe a humidity sensor 00:07:59.90900:07:59.919 we can tell that the air coming in has a 00:08:02.94000:08:02.950 relative humidity of 70 percent and with 00:08:06.24000:08:06.250 these two values here that means we can 00:08:08.10000:08:08.110 look up all the these other values here 00:08:11.13000:08:11.140 such as the specific volume the enthalpy 00:08:13.62000:08:13.630 and also the specific humidity and 00:08:16.77000:08:16.780 you'll have to look these up in the air 00:08:17.94000:08:17.950 property tables you can just google 00:08:20.19000:08:20.200 these it's very quick and easy to do or 00:08:22.74000:08:22.750 just find an online air properties 00:08:24.81000:08:24.820 calculator now the supply air that's 00:08:27.93000:08:27.940 coming out of the fan coil unit or the 00:08:29.61000:08:29.620 air here tube we're measuring it here 00:08:31.83000:08:31.840 and we know that that air is coming out 00:08:33.75000:08:33.760 of 15 degrees Celsius with a relative 00:08:36.57000:08:36.580 humidity of 100% and from those two 00:08:40.07900:08:40.089 values we can then 00:08:41.55000:08:41.560 cup the enthalpy and also the specific 00:08:43.89000:08:43.900 humidity for this airflow also so 00:08:47.64000:08:47.650 obviously that air has cooled down from 00:08:49.74000:08:49.750 30 degrees Celsius down to 15 degrees 00:08:52.47000:08:52.480 Celsius and that's because the cooling 00:08:54.60000:08:54.610 coil here is an operation so flowing 00:08:59.73000:08:59.740 through this cooling coil is the chilled 00:09:02.28000:09:02.290 water and that is flowing at a rate of 00:09:04.65000:09:04.660 four point six seven kilograms per 00:09:06.84000:09:06.850 second the water coming in is at six 00:09:10.07900:09:10.089 degrees Celsius and from that we can 00:09:13.71000:09:13.720 look up and tell that the specific heat 00:09:16.14000:09:16.150 capacity is at four point two kilojoules 00:09:18.99000:09:19.000 per kilogram per Kelvin but we don't 00:09:22.68000:09:22.690 know yet what the temperature out is 00:09:25.86000:09:25.870 going to be on that core but we can 00:09:27.39000:09:27.400 calculate that also now this air is also 00:09:32.25000:09:32.260 condensing because it's coming in very 00:09:34.17000:09:34.180 warm and leaving very cool at a hundred 00:09:36.93000:09:36.940 percent relative humidity so that the 00:09:40.11000:09:40.120 moisture in that air is condensing on 00:09:42.21000:09:42.220 this cooling coil and that is then 00:09:44.34000:09:44.350 flowing a way out to drain and we know 00:09:48.03000:09:48.040 that that water is going to be at a 00:09:50.40000:09:50.410 temperature of this out here so that's 00:09:52.80000:09:52.810 going to be at fifteen degrees Celsius 00:09:54.42000:09:54.430 and and we can look that up the enthalpy 00:09:57.45000:09:57.460 for that which will be you'll have the 00:09:59.82000:09:59.830 fine ease in the saturated steam tables 00:10:01.95000:10:01.960 and that you'll see that there is going 00:10:04.86000:10:04.870 to be at 63 kilojoules per kilogram and 00:10:07.98000:10:07.990 we can also calculate how much water is 00:10:11.10000:10:11.110 actually flowing out of there from this 00:10:12.54000:10:12.550 air that's coming in so of this air 00:10:15.12000:10:15.130 that's coming in there's obviously two 00:10:16.14000:10:16.150 parts to that there is air that's coming 00:10:19.02000:10:19.030 in and then there's also moisture which 00:10:20.82000:10:20.830 is in the end so we can calculate how 00:10:23.19000:10:23.200 much just pure air is in there so that 00:10:25.56000:10:25.570 it's called the dry dry air and the the 00:10:28.77000:10:28.780 mass flow rate of that coming in the 00:10:30.51000:10:30.520 amount of flow rate of air coming in 00:10:34.07000:10:34.080 without any moisture that is the m dot 00:10:37.71000:10:37.720 the dot just represents a rate of flow a 00:10:41.03000:10:41.040 represents the the air 00:10:43.15000:10:43.160 so it's the volume flow rate you can see 00:10:46.48000:10:46.490 up here divided by the specific volume 00:10:49.30000:10:49.310 also of that air coming in and obviously 00:10:52.33000:10:52.340 that is a number there is specific to 00:10:55.48000:10:55.490 the air at these conditions so when we 00:11:00.07000:11:00.080 drop these numbers in which are just 00:11:01.45000:11:01.460 coming from up here this comes out at 00:11:04.27000:11:04.280 two point two two kilograms per second 00:11:06.79000:11:06.800 of air dry air coming into this cooling 00:11:09.94000:11:09.950 unit I also mentioned that there is 00:11:12.46000:11:12.470 condensate water that's water that's 00:11:14.53000:11:14.540 being extracted from this warm air and 00:11:17.38000:11:17.390 it's being discharged down to drain so 00:11:19.93000:11:19.940 we can calculate the flow rate of that 00:11:21.70000:11:21.710 as well so so the condensate mass flow 00:11:27.10000:11:27.110 rate that's the water so it's MDOT and 00:11:29.68000:11:29.690 the W represents just water and we can 00:11:34.21000:11:34.220 use this formula here which is the mass 00:11:36.61000:11:36.620 flow at the flow rate of the air which 00:11:38.65000:11:38.660 we just calculated multiplied by the 00:11:42.70000:11:42.710 difference in the specific humidity and 00:11:46.45000:11:46.460 that gives us naught point naught to two 00:11:48.46000:11:48.470 kilograms per second and that's of water 00:11:50.94000:11:50.950 flowing out of this so from all this we 00:11:54.85000:11:54.860 can then calculate the cooling load and 00:11:57.31000:11:57.320 that's represented by the Q that formula 00:12:01.57000:12:01.580 is just the summary of the mass flow 00:12:05.26000:12:05.270 rate of the air multiplied by the 00:12:07.77000:12:07.780 difference in enthalpy across these two 00:12:11.02000:12:11.030 air streams in addition to 00:12:13.89000:12:13.900 multiplication of the mass flow rate of 00:12:16.51000:12:16.520 the water multiplied by the enthalpy of 00:12:19.54000:12:19.550 the condensate water also and you can 00:12:22.69000:12:22.700 see I've color-coded these numbers as 00:12:24.34000:12:24.350 well so you should be able to just trace 00:12:26.32000:12:26.330 these out if you was to get stuck trying 00:12:27.88000:12:27.890 to work this out yourself so when we 00:12:30.52000:12:30.530 drop these numbers in you should see 00:12:32.35000:12:32.360 that this comes out at seventy eight 00:12:34.39000:12:34.400 point five kilojoules per second which 00:12:36.70000:12:36.710 is also obviously seventy eight point 00:12:39.28000:12:39.290 five kilowatts so that means that this 00:12:42.22000:12:42.230 cooling coil is extracting seventy eight 00:12:45.46000:12:45.470 point five kilowatts or thermal energy 00:12:47.65000:12:47.660 from this air stream and once we know 00:12:50.65000:12:50.660 that we can then calculate what the 00:12:53.17000:12:53.180 water off temperature is going to be so 00:12:55.84000:12:55.850 vit 00:12:56.42000:12:56.430 water the chilled water is leaving this 00:12:58.70000:12:58.710 cooling coil what temperature that's 00:13:00.82900:13:00.839 going to be at so the temperature out 00:13:03.86000:13:03.870 the T out is equal to temperature in 00:13:07.73000:13:07.740 plus the cooling load divided by the 00:13:11.00000:13:11.010 mass flow rate of this water that's 00:13:13.55000:13:13.560 passing through and that multiplied 00:13:16.49000:13:16.500 against the specific heat capacity again 00:13:19.40000:13:19.410 all these figures are color-coded so you 00:13:21.26000:13:21.270 should be able to just find these and 00:13:23.42000:13:23.430 plot them in if you've got an example 00:13:24.62000:13:24.630 yourself to work out so when we drop 00:13:27.71000:13:27.720 these figures in you should see that the 00:13:29.54000:13:29.550 temperature of the T out is equal to ten 00:13:33.07900:13:33.089 degrees Celsius 00:13:34.10000:13:34.110 so that water is coming in at six 00:13:36.82900:13:36.839 degrees Celsius and leaving at 10 degree 00:13:39.35000:13:39.360 Celsius going back to the chiller okay 00:13:42.13900:13:42.149 that is it for this video thank you very 00:13:43.76000:13:43.770 much for watching if you've got any 00:13:45.59000:13:45.600 questions please leave them in the 00:13:46.73000:13:46.740 comment section below don't forget to 00:13:49.13000:13:49.140 Like and subscribe to the channel and 00:13:50.75000:13:50.760 feel free to share the video with anyone 00:13:53.69000:13:53.700 you think it might help also once again 00:13:56.26900:13:56.279 thanks for watching
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