Power and the Glory

Part 1 — There’s a hole in the bucket

Being the first part in a four (five) part trilogy on power, energy and the loss of same.

Fair warning: if “tl;dr” to you means “anything longer than the footy betting pool coupon”, stop reading. It’ll be longer than that.

This power lark …

When, not long ago, the price of a kilowatt–hour energy reached half a quid in our area of Sweden, we sat down to think.

The house, for various reasons that’ll become apparent, use in the neighbourhood of 35,000 kWh per year. Worst case — so far — that’s a cool 16,800 pounds. Sterling. The house is the bucket, and there’s a bad leek in it. Time to think harder.

As for the building itself: 2000sqft built in 1984 to the specs of the time. It’s not poorly insulated, has triple–pane windows, double–layer stone wool in the ceiling, hydronic heating … and, admittedly, some draught reducing sealing–strips that are in dire need of replacement.

The main problem was with the hot water storage tank, all 1,300 litres of it. A hydronic heating system works by having a gargantuan tank of water — called an “accumulator tank” — , that one heat by various means (oil, electricity, furnace, e.t.c.).

Said hot water is pumped through the house, via a series of radiators, each one emitting heat. Once the water is returned to the tank, rinse and repeat.

Here’s the rub: the system they installed in ‘84 is just a little bit different. Inside the storage tank resides a copper spiral which is connected, on one side, to the cold water pipe from the well. On the other side it connects to the hot water system — aka shower, bathtub, taps.

Can you spot the problem? During winter, temperatures here can fall to –28C. The heating system can handle that, no problem. During summer, it can rise to +35 in brief periods … and during that time we still need to heat 1,300 litres of water to be able to shower. Vimes had the right of it.

As cold water flow into the tank it gets heated and water in the tank gets chilled. After not too long the shower is as cold as the radiators … ok, ok — a tiny bit of exaggeration there.

It’s a pretty nasty detail, and responsible for the majority of our power usage.

If we disregard the fact that hydronic systems require piping inside the walls, all through the house, with the subsequent maintenance problem, it’s a pretty good way to heat a home. No “dry” heat; no possibility of a fire due to exposed heating elements and so forth — and no requirement to actually heat the water using electricity.

Of course, there’s also the bit about the tank itself — while well insulated it still emit heat. Underneath the bedroom we’d sorely want to keep cool.

Heat Pumps

Classified in my book under “minor miracle”, a heat pump is a pretty nifty way to cheat on Mother Nature with, well, Mother Nature: take one cold liquid (the “brine”, typically containing alcohol or glycol to stop it freezing) and pump it through a medium (aka “air” or “water” or … ) by which it is warmed (a few degrees).

The brine is used to heat an even colder liquid (the “refrigerant” typically, today, carbon dioxide or similar) in a closed system – again just a few degrees. At this point the refrigerant change state to a gaseous form, and is run through a compressor. When compressing a gas, it heats up quite a lot; it’s can now be used to heat the water in the hydronic system. From a brine of 4C one can get 60C by way of this little trick.

“This has what to do with electricity?!” I hear you cry. The problem with the existing system is that we use power from the grid (the grid == our local power company) in other to heat water by way of resistance — i.e. push power through a piece of metal and the metal will heat up. Submerge the metal in water and the water will heat up.

Contrast this with a heat pump: the power from the grid needed to run the system is far less because most of the energy is extracted from the environment; a 1kWh grid feed–in produce between 3–5kWh energy in the form of heat. This is known as the COP factor — of which an electric resistance element has 1 (1.0, but who’s counting).

Heat pumps using air as the medium with air–based heating (air–air HP) yields approx. 2.0; air–water (i.e. hydronic, but air as medium) around 3.0; ground source heat pumps COP about 5.

We wants loads of COP, of course. Since the house stands firmly on Scandinavian granite, and the best values spring from down–hole heat exchangers (phew!), the next step was obvious.

Worth a minor note: hydronic heating systems come in two flavours1 one, referred to as “high temperature”, pump water at around 55°C through a system of copper pipes in a house wall and further through radiators normally mounted underneath windows in each room. Since the heating pump must produce a higher amount of heat, the COP is ca. 4.

A “low temperature” system does the same, but pump the water through a series of pipes installed in the floor. The temperature here is around 45°C, and the COP is subsequently higher — approx. 5.

Ours is the first kind, luckily. Leaks in the floor is a nasty thing.

Ground–based heat

The “medium” — cast your mind to that bit above — is the source of the environmental energy used to, ultimately, heat the water, and the best such is the one with a stable temperature year round: the actual, physical planet.

Ground heat can be extracted in a variety of ways, but the most common method is to drill a deep hole and run a flexible tube down it (and up!) and circulate the brine through the tube.

Time to throw out a request to tender. This stuff, fiddling about with various forms of water pipes and power couplings, we do not do ourselves. Uh–huh. Build a garage, fine. Rebuild an engine, fine. Water pipes? Hell no.

As is the recommended practice we evaluated three different bids and ended up with a local installation company, a local drilling company and a local manufacturer of heat pumps. We rather believe in “local”.

These three2, for a not a terrible lot of money, provided a 200m deep, 114mm wide hole in the lawn, a complete set of pipes, fixings and thingamabobs, as well as a Nibe S12553 heat pump.

“But!” — yes, I hear you cry. Its unseemly in an adult; really, it is. We’ll get to the money in a moment.

The old tank was cut to pieces and removed4, the boiler–room was renovated, installation was completed, and the new system turned on late May 2021. A year or so later we can conclude that

All in all a good result — as illustrated by the light blue line on the right …

It sadly leaves us with an approximately 16,800 kWh usage. That ain’t so good — for the environment, for the bill or for relaxed nocturnal activities.

Onwards and upwards. (Or: see part 2)

PS

The more thermodynamic–ally inclined might have spotted an obscure detail in the above: the brine, when it emerges from the bore–hole, holds a temperature of some 4 degrees Celsius. Why not use that as the basis for cooling?

And so we do. At a minuscule cost we can, during summer, use the brine to cool air in our home office by way of a Sabiana fan coil unit. Benefits all around :)


1 Yes, there are more than two types, but this isn’t a PhD thesis.

2 Our thanks to Iskristallen AB for a thoroughly professional hole in the lawn, BJ Värmemontage AB for plugging pipes into thingamabobs, and NIBE Energy Systems for the reversed refrigerator thingie.

3 “Nibe whatsits?!” — NIBE Energy Systems is a Swedish company who, since 1952, has produced heating solutions of various types. We rather like the thought of local manufacturing. As the NIBE also fit the bill, crossed every t and dotted every i, and a local, certified, installer had the best bid…. Robert is your father’s brother5

4 The 1,300 litre boiler was so large that it had to have been installed prior to the floor above put in place. It certainly didn’t fit through the door! We had a couple of blokes with an angle grinder and loads of energy take it apart.

5 Bob’s yer uncle.

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