“Choosing” — deciding how to allocate finite, limited resources is a central, recurring theme in these explorations.
To recap some previous thoughts, there are perhaps three components to making good decisions:
Information — we need data and facts.
Critical thinking — we need to be able to discern which facts are important and the “quality” of those facts, which we can have confidence in.
Decision-making methods and tools — analytical tools to assist us in determining facts and testing their quality and importance.
This process is in contrast to simply accepting “information” as presented. If the “information” we are given is not well-founded, it really can’t be used as information. It is important to separate the “wheat from the chaff.”
In complex societies, we seem to often have information supplied with built-in, hidden, and maybe intentional biases. We may never know the intention of these hidden biases — the point is that we have to do our own work to find out which facts we can trust.
A simple case study in critical thinking: Heat-Recovery Drains
Let’s accept that we have might have a goal to “save money, conserve resources, consume less energy, reduce our impact on the non-human environment (implying “save the planet”).”
So if we are presented with a simple, understandable, and tangible way to accomplish these things, that would be of interest, right.
So what if you were aware of the waste of the heat in the hot water we let run down the drains of our houses? And what if someone presented you with a simple way of recovering some of that waste — saving that energy? That would seem to be unquestionably a good idea!
Some clever person devised or invented the “heat recovery drain.” The intention is to recapture some of the heat we paid for in the hot water we use in our homes.
The device is brilliantly simply: Wrap a copper manifold of many small copper tubes around the main vertical drain in a house. Turn on a hot water tap in the house and hot water is drawn from the hot water heater, typically a tank. As hot water is drawn from the top of the tank, cold water, under pressure from the city supply, is pushed into the bottom of the tank, where an electrical element or gas-burning flame will heat it ready for use. In this idea, the cold water first travels through the copper manifold around the drain pipe, where the hot water, coming out of the hot water tap eventually passes on it way to the sewer. The heat, now reduced somewhat, passes its heat to the incoming cold water, pre-heating it before it goes to the hot water tank, reducing the amount of energy required to bring the water up to the desired temperature.
“Genius!” “Free energy!” It obviously makes sense and we should install one in every home!
Bullshit.
What? Why?
Apply a bit of critical thinking, some basic physics, and some simple economics.
If the supply and installation of the heat-recovery manifold was free, this might make some sense. But they’re not.
Let’s apply some simple physics: Hot things lose heat to the space and matter around them. The hot water coming out of the hot water tank has lost heat to the pipes that carry it and air around them as it travels to the point of use. It loses more heat as it pours from the faucet through the air, and more as it drips off the facecloth back into the sink. And then it loses more heat into the pipes that carry it to the main drain.
For the sake of argument, let’s pretend that 50% of the heat that water originally contained is still present when the water reaches the recovery drain (Hugely and unreasonably optimistic.).
Looking at a typical small North American household of 4 people (our house) we can examine the gas bill. Deducting the “service fee” the utility charges whether we use gas that month or not, and looking at summer consumption (therefore, no space-heating consumption, only hot water), I calculate that we use about $7.00 of gas each month. Let’s round it up to $100/year.
So this unit can save me $50/year.
The unit can cost between $500 and $1,000 and there is a cost for installation that I am told can double the cost.
So there is a straight payback, ignoring the “time-value of money,” of 10 to 20 years. Note that the “time value of money” is not trivial. If your neighbour, instead, took that money and invested it at a 5% return, your bank account would never get ahead.
That’s not good.
But wait! The real story is much worse. That hypothetical and unrealistic 50% saving applies ONLY to water that is flowing down the drain at the same time that water is flowing into the hot water tank.
Imagine what happens when you pour a bath. You turn on the hot water tap and the bath fills with hot water. Cold water comes in from the water main and passes through the heat recovery manifold. But there is no hot water coming down the drain because it is all being held in the tub. Later, when the tub is draining, there is no cold water passing through the heat-recovery drain because the tank is full and no water is being drawn into it.
So all that heat goes down the drain. The same applies for a dishwasher, a basin or sink of water, or the washing machine. The demand for hot water does not happen at the same time as when the warm water drains away.
In those cases the heat-recovery drain is not recapturing any heat . . . and they can represent the majority of a household’s hot water consumption.
So the payback period has become infinite.
Yet, in some kind of twisted logic governments are providing subsidy grants to encourage the installation of these things! Worse, some municipalities are now requiring builders to install them, adding to the cost of houses with no economic benefit. In fact, the latest Ontario Building Code also requires their installation.
This is a misallocation of resources. The same money could be spent on something that might create an actual benefit. There is a real opportunity cost, beyond simply making housing even a bit more unaffordable.
Someone can argue that the government subsidies can make it economical for homeowners. This ignores the cost of the taxes governments collect in order to pay for these subsidies. Government subsides just confuse the issue and magnify the waste, or misallocation of resources.
Heat recovery drains do not save the planet. The emperor has no clothes.