Saturday, April 29, 2017
Vicious AC cycle: 1 cooling to you gives 15 heating to Atmos
These days, you're either subject to the harshness of the (natural) oven or you are under the benevolence of an air conditioner. I played cricket past two Saturdays, and got absolutely taken out. Before I could hit any stroke, the sun hit its stroke and I was down for the count. My friend ST's whatsapp status reads "Invincible summer".
(Distracting pun here; did not want to disturb the flow of the para above: A good sun stroke hits the sweat spot while a good cricket stroke hits the sweet spot)
Firstly, we corporate MBA types have been spoilt by air conditioning. As a kid in Delhi, my "PT" class was the last, and I would run around between 1 and 2 PM with merry abandon. Now look at me!
Secondly, coming to the nub of the matter here. So, it's getting hotter. We use the AC for longer hours. We expel all the heat from the heat exchanger, and make it even further hotter outside. Further, we've anyway generated more than 50% of our electricity from coal, having already added a good amount of CO2 to the atmosphere. What's going to stop this vicious thermodynamic cycle? I'm just saying thermodynamic because I remember all those Pressure and Enthalpy cycles we used to plot during UG days (Thermodynamics 101), and also perhaps to add some gravitas to the writing.
Actually going to the thermodynamic heart of it, the underlying thermodynamic cycles of thermal power generation and the air conditioning are inherently inefficient- can't go to 100 no-sir-no. The efficiency of ACs in India (some kind soul did a survey, link below) is 20%. On top of that, factor in the 30-40% efficiency of coal plants (wikipedia confirming vague memory from "Power Plant Engineering" course; that's around the theoretical maximum of the "Rankine cycle"). And then the 20% transmission losses to get it to you here via power lines. So when NTPC burns coal, only 0.2*0.4*0.8 =6% of that is coming to you. Rest is all heat dissipated into the atmosphere.
One way to think about it: for one cooling unit into your room, you have let out 15 units of heating into the atmosphere. As you put out 15 units, it becomes hotter. And you have to release 2 units of cooling into your room in the next hour. But wait, you've released 30 units now.
Now I'm supposed to give solutions, like a lame, formulaic essay? Ok, so go out in the sun in the mornings, and thus get used to the heat more, and after that maybe you'll need the AC less number of hours. The 175 GW Solar target set by GoI will help. Lastly, watch the lights at home. If not the AC, save in some other form. Oh, and read the biography of Elon Musk, so that you get inspired and purchase a Tesla (whenever feasible) and install solar on your roof. Oh, and you upwardly mobile MBA types- purchase a fuel efficient car, not an SUV.
Link to kind soul's work: http://consumeraffairs.nic.in/consumer/writereaddata/splitac.pdf
(Distracting pun here; did not want to disturb the flow of the para above: A good sun stroke hits the sweat spot while a good cricket stroke hits the sweet spot)
Firstly, we corporate MBA types have been spoilt by air conditioning. As a kid in Delhi, my "PT" class was the last, and I would run around between 1 and 2 PM with merry abandon. Now look at me!
Secondly, coming to the nub of the matter here. So, it's getting hotter. We use the AC for longer hours. We expel all the heat from the heat exchanger, and make it even further hotter outside. Further, we've anyway generated more than 50% of our electricity from coal, having already added a good amount of CO2 to the atmosphere. What's going to stop this vicious thermodynamic cycle? I'm just saying thermodynamic because I remember all those Pressure and Enthalpy cycles we used to plot during UG days (Thermodynamics 101), and also perhaps to add some gravitas to the writing.
Actually going to the thermodynamic heart of it, the underlying thermodynamic cycles of thermal power generation and the air conditioning are inherently inefficient- can't go to 100 no-sir-no. The efficiency of ACs in India (some kind soul did a survey, link below) is 20%. On top of that, factor in the 30-40% efficiency of coal plants (wikipedia confirming vague memory from "Power Plant Engineering" course; that's around the theoretical maximum of the "Rankine cycle"). And then the 20% transmission losses to get it to you here via power lines. So when NTPC burns coal, only 0.2*0.4*0.8 =6% of that is coming to you. Rest is all heat dissipated into the atmosphere.
One way to think about it: for one cooling unit into your room, you have let out 15 units of heating into the atmosphere. As you put out 15 units, it becomes hotter. And you have to release 2 units of cooling into your room in the next hour. But wait, you've released 30 units now.
Now I'm supposed to give solutions, like a lame, formulaic essay? Ok, so go out in the sun in the mornings, and thus get used to the heat more, and after that maybe you'll need the AC less number of hours. The 175 GW Solar target set by GoI will help. Lastly, watch the lights at home. If not the AC, save in some other form. Oh, and read the biography of Elon Musk, so that you get inspired and purchase a Tesla (whenever feasible) and install solar on your roof. Oh, and you upwardly mobile MBA types- purchase a fuel efficient car, not an SUV.
Link to kind soul's work: http://consumeraffairs.nic.in/consumer/writereaddata/splitac.pdf
Labels: Musings
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