What Is a Heat Pump?

Heat pumps are all the fad as of late, notably in Europe, the place some international locations are striving to ban the set up of fossil-fuel fired furnaces and boilers in favor of greener choices, together with energy-saving warmth pumps. (Furnaces warmth air and distribute it all through homes utilizing ducts, whereas boilers warmth water to supply sizzling water or steam for heating.) And this yr the U.S. authorities started providing tax incentives for the set up of warmth pumps, which are inclined to value extra up entrance than conventional furnaces however are much more environment friendly in the long term. So perhaps it’s time to come back in control on what a warmth pump is and does.

What is the commonest kind of warmth pump?

Given all of the current buzz, you may be stunned to study that you simply use warmth pumps already—there’s in all probability multiple in your house and one other in your automotive. You simply don’t name them warmth pumps: You use the phrases fridge or air conditioner.

These machines are, in reality, warmth pumps, which means that they transfer warmth from a place the place it’s comparatively chilly to a place the place it’s comparatively sizzling. Heat flows by itself from sizzling to chilly. But if you wish to transfer it from chilly to sizzling, you could “pump” it. The finest analogy right here is with water, which flows downhill by itself however must be pumped uphill.

Workers set up coiled tubing to hold the heat-exchange fluid for a ground-source warmth pump.iStock

When you pump warmth that’s contained in a chilly reservoir of some type (air, water, no matter) to a heat one, the chilly reservoir will get colder and the nice and cozy one will get hotter. And that’s actually all of your fridge or air conditioner does—it strikes warmth from the place it’s not wished to some other place, the place you don’t care that you simply’re dumping a little further warmth.

How does a warmth pump transfer warmth from chilly to sizzling?

You may be asking your self at this level: How is it even potential to pump warmth from chilly to sizzling? Put one other approach: How does a fridge work? The fundamental precept isn’t obscure, notably with the assistance of a thought experiment.

Imagine you’ve a bottle of wine you need to chill, however you haven’t any fridge. Maybe you’re on a tenting journey, and also you don’t have entry to something that’s colder than your room-temperature wine. You do, although, have a bottle of equally tepid 176-proof vodka available.

The reply to this riddle, when you’ve not figured it out already, is to pour some vodka over the bottle of wine. The vodka is 88 % alcohol, and as that alcohol evaporates, it’ll cool the wine a little. The precept at work right here takes benefit of what’s referred to as the latent warmth of vaporization. In a nutshell, evaporation of the alcohol takes away some warmth vitality from the wine bottle, cooling it barely. After the vodka coating the floor of the wine bottle evaporates, rinse (with extra vodka) and repeat, cooling the wine bottle a little extra with every dousing.

The drawback, in fact, is that vodka is dear, and also you’ll quickly use all of it up chilling the wine. Even when you changed the vodka with cheaper rubbing alcohol, you’d quickly be bemoaning the expense.

How are you able to make a sensible chiller with a warmth pump?

The key perception that led to the warmth pump got here within the early nineteenth century, when numerous inventors, together with Jacob Perkins, realized that they may cool one thing this fashion with out squandering the risky liquid they evaporated to attain cooling. Instead of releasing these vapors into the ambiance, they reckoned, you can acquire them, condense them again into a liquid, and reuse that liquid because the coolant.

That’s precisely what your fridge and air conditioners do. They evaporate a liquid refrigerant and use the chilly vapor to absorb warmth from inside your icebox or automotive. They then compress that gasoline, which condenses again into liquid kind. That liquid is now hotter than it began out, so among the warmth it holds flows simply (probably with the assistance of a fan) into the encompassing surroundings—be that the good open air or simply the remainder of your kitchen.

All that’s to say: You are very accustomed to warmth pumps; it’s simply that you simply’ve been calling them air conditioners and fridges.

Let’s now conduct one other thought experiment. If you’ve a window air conditioner, you would possibly even do that as an precise experiment. Install it backwards. That is, set up it with the controls on the exterior of your window. Do this on a considerably cool and dry day. What occurs?

As you’d anticipate, it blows chilly air into your yard, and it releases warmth into your private home. So it’s nonetheless pumping warmth, making your private home extra comfy by warming it. Sure, it’s making the air colder exterior, however the impact can be vanishingly small when you get any distance away from the window.

You now have a warmth pump warming your private home. It may not be the perfect warmth pump, however it’ll work. What’s extra, when summer time rolls round, you may flip it round once more and use it as an air conditioner.

Don’t truly do that, in fact. If you tried, it might little doubt fail the primary time it rained and water obtained into the controls. Instead, go purchase your self a industrial “air-source” warmth pump, which can heat your private home utilizing the exact same precept.

You are very accustomed to warmth pumps; it’s simply that you simply’ve been calling them air conditioners and fridges.

Some of those models have what is called a reversing valve, which permits the identical gear to serve double obligation: They can pump warmth from exterior to inside or from inside to exterior, offering each warmth and air-conditioning, as defined beneath.

Double-Duty Heat Pumps

A warmth pump used for heating is mainly the identical as an air conditioner. Both comprise piping that carries a risky fluid round in a circuit, a compressor, and two warmth exchangers, one indoors and one open air.

Some warmth pumps make the most of this similarity to perform as each heaters and air conditioners. To achieve this, they use what’s referred to as a reversing valve, which permits the risky fluid within the piping to be despatched in both course. Each warmth exchanger can then be used both to supply warmth or to soak up warmth.

Why are warmth pumps extra environment friendly than electrical heaters?

Heat pumps are extra environment friendly than electrical heaters as a result of they don’t must generate warmth from electrical energy. The electrical energy a warmth pump makes use of does create some warmth alongside the way in which, however extra vital is that it pumps warmth from exterior into your private home. The ratio of the warmth launched into your private home to the vitality despatched into its electrically pushed compressor is known as the coefficient of efficiency, or COP for brief.

A easy electrical area heater, which generates all the warmth it offers from an electrically heated aspect, has a COP of 1. A warmth pump, then again, can have a COP that’s an order of magnitude larger.

The COP for a warmth pump just isn’t a fastened worth, although. It varies inversely with the distinction in temperature between the 2 reservoirs between which warmth is pumped. That is, if you’re pumping warmth from a not-so-very-cold reservoir into a not-so-very-hot constructing, the COP can be a massive worth, which means that your warmth pump could be very environment friendly in the way it makes use of electrical energy. But when you attempt to pump warmth from a terribly chilly reservoir into an already balmy constructing, the COP could have a decrease worth, which means that effectivity suffers.

The result’s what you’d intuitively anticipate: It’s finest to make use of as your out of doors reservoir of warmth one thing that’s as heat as you’ll find.

Air-source warmth pumps, which use the out of doors air as that reservoir of warmth, are the worst selection on this regard, as a result of the out of doors air could be very chilly throughout winter heating season. Better could be a ground-source warmth pump (additionally referred to as a geothermal warmth pump), as a result of even in winter the bottom at a modest depth stays fairly heat.

What’s the perfect supply of warmth for a warmth pump?

The rub with ground-source warmth pumps is that you simply want a technique to entry this buried reservoir of warmth. If you’ve ample area round your private home, you may dig trenches and bury a bunch of piping at a affordable depth, say, a couple of meters down. You can then flow into a liquid (usually a mixture of water and antifreeze) by way of these pipes to soak up warmth from the bottom. Or you may have deep boreholes drilled into the bottom and have piping put in vertically into these holes. All that will get costly, although.

Another tactic, obtainable to the fortunate few, is to extract warmth from a close by physique of water, by submerging piping at some depth in that water. These are known as water-source warmth pumps. Some warmth pumps use extra uncommon methods, whereby warmth is extracted from the air leaving the constructing or from solar-heated water.

In very chilly climates, it is smart to put in a ground-source warmth pump when you probably can. That’s probably why many of the warmth pumps in Sweden—a nation with one of many highest numbers of warmth pumps per capita—are of this selection. But even Sweden has a good share of air-source warmth pumps, which belies the frequent assertion (at the very least within the United States) that warmth pumps are solely good for heating properties in gentle climates.

So irrespective of the place you’re situated, when you can afford the upper up-front prices, take into account a warmth pump over a conventional furnace or boiler subsequent time you’re confronted with the choice about how one can warmth your private home.