What Is a Heat Pump?

Warmth pumps are all the craze nowadays, significantly 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 offer scorching 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 price extra up entrance than conventional furnaces however are way more environment friendly in the long term. So perhaps it’s time to return on top of things on what a warmth pump is and does.

What’s the commonest kind of warmth pump?

Given all of the latest buzz, you is perhaps stunned to study that you simply use warmth pumps already—there’s most likely multiple in your house and one other in your automobile. You simply don’t name them warmth pumps: You utilize the phrases fridge or air conditioner.

These machines are, actually, warmth pumps, which means that they transfer warmth from a spot the place it’s comparatively chilly to a spot the place it’s comparatively scorching. Warmth flows by itself from scorching to chilly. However if you wish to transfer it from chilly to scorching, it is advisable “pump” it. The most effective analogy right here is with water, which flows downhill by itself however must be pumped uphill.

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

Whenever 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 elsewhere, the place you don’t care that you simply’re dumping slightly additional warmth.

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

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

Think about you could have a bottle of wine you wish to chill, however you don’t have any fridge. Possibly 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 readily available.

The reply to this riddle, for those who’ve not figured it out already, is to pour some vodka over the bottle of wine. The vodka is 88 p.c alcohol, and as that alcohol evaporates, it’ll cool the wine slightly. The precept at work right here takes benefit of what’s referred to as the latent heat 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 slightly extra with every dousing.

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

How will you make a sensible chiller with a warmth pump?

The important thing perception that led to the warmth pump got here within the early nineteenth century, when numerous inventors, together with Jacob Perkins, realized that they might cool one thing this fashion with out squandering the risky liquid they evaporated to attain cooling. As an alternative of releasing these vapors into the ambiance, they reckoned, you may acquire them, condense them again right 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 take in warmth from inside your icebox or automobile. They then compress that fuel, which condenses again into liquid kind. That liquid is now hotter than it began out, so a number of the warmth it holds flows simply (possible with the assistance of a fan) into the encircling setting—be that the nice outside or simply the remainder of your kitchen.

All that’s to say: You’re 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. In case you have a window air conditioner, you may even do that as an precise experiment. Set up it backwards. That’s, set up it with the controls on the outdoors of your window. Do that 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 own home. So it’s nonetheless pumping warmth, making your own home extra comfy by warming it. Certain, it’s making the air colder outdoors, however the impact can be vanishingly small when you get any distance away from the window.

You now have a warmth pump warming your own home. It won’t be one of the best 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 really do that, in fact. Should you tried, it will little doubt fail the primary time it rained and water acquired into the controls. As an alternative, go purchase your self a business “air-source” warmth pump, which can heat your own home utilizing the exact same precept.

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

A few of these models have what is named a reversing valve, which permits the identical tools to serve double obligation: They’ll pump warmth from outdoors to inside or from inside to outdoors, offering each warmth and air-conditioning, as defined beneath.

Double-Responsibility Warmth Pumps

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

Some warmth pumps benefit from this similarity to perform as each heaters and air conditioners. To take action, they use what’s generally known as a reversing valve, which permits the risky fluid within the piping to be despatched in both route. Every warmth exchanger can then be used both to offer warmth or to soak up warmth.

Why are warmth pumps extra environment friendly than electrical heaters?

Warmth pumps are extra environment friendly than electrical heaters as a result of they don’t have to generate warmth from electrical energy. The electrical energy a warmth pump makes use of does create some warmth alongside the best way, however extra necessary is that it pumps warmth from outdoors into your own home. The ratio of the warmth launched into your own home to the vitality despatched into its electrically pushed compressor is known as the coefficient of performance, or COP for brief.

A easy electrical house heater, which generates all the warmth it gives from an electrically heated component, has a COP of 1. A warmth pump, however, can have a COP that’s an order of magnitude increased.

The COP for a warmth pump is just not a set worth, although. It varies inversely with the distinction in temperature between the 2 reservoirs between which warmth is pumped. That’s, in case you are pumping warmth from a not-so-very-cold reservoir right into a not-so-very-hot constructing, the COP can be a big worth, which means that your warmth pump could be very environment friendly in the way it makes use of electrical energy. However for those who attempt to pump warmth from a very chilly reservoir into an already balmy constructing, the COP may 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 outside reservoir of warmth one thing that’s as heat as you will discover.

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

What’s one of the best supply of warmth for a warmth pump?

The rub with ground-source warmth pumps is that you simply want a option to entry this buried reservoir of warmth. In case you have ample house round your own home, you may dig trenches and bury a bunch of piping at an inexpensive depth, say, a few meters down. You may then flow into a liquid (sometimes a mixture of water and antifreeze) by means 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.

One other tactic, accessible 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 sensible to put in a ground-source warmth pump for those who presumably can. That’s possible why a lot of the warmth pumps in Sweden—a rustic with one of many highest numbers of warmth pumps per capita—are of this selection. However even Sweden has a superb share of air-source warmth pumps, which belies the widespread assertion (not less than in the US) that warmth pumps are solely good for heating properties in delicate climates.

So regardless of the place you’re situated, for those who can afford the upper up-front prices, think about a warmth pump over a conventional furnace or boiler subsequent time you’re confronted with the choice about learn how to warmth your own home.