Air Conditioner to Heat Pump conversion - Does it work? Is it worth it?

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Veröffentlicht am: 01.05.2024
 

The main theme of the article is the trend of converting air conditioners into heat pumps - a broad and multifaceted topic. We'll try to delve into it as comprehensively as possible, considering most of its aspects. We'll focus on the air-to-water heat pump specifically, which is intended to heat homes with traditional heating systems (i.e., water-based - using radiators or even better, underfloor heating). The article will carry elements of a DIY (Do It Yourself) approach, but it's not necessarily an attempt to discourage "professional" heat pump solutions. Instead, we aim to familiarize the reader with the topic.

Air conditioner as a heat pump - how much does it cost and is it worth it?

Costs, undoubtedly the primary motivation for individuals choosing to utilize an air conditioner as a heat pump instead of purchasing a ready-made solution from a company offering heat pump systems.
✅ Undoubtedly, using an air conditioner as a heat pump is a cheaper solution, roughly ranging from 1000 € to 5000 €, while ready-made devices (with comparable parameters) cost from 4000 € to 15000 €. However, the lower end of the range - 1000 € - would likely require the use of an older type of air conditioning unit without an inverter, which can affect its later quality of use and costs. To make it worthwhile, one should expect to spend several thousand zlotys or more.

Most people would therefore argue that it is worth it - although there are also those who consider it not cost-effective - but let's be honest, for them to deem it so, they must be able to afford it. So, undoubtedly, the price is tempting, but behind it are specific solutions that need to be analyzed.
A lot remains in the pocket, so what exactly are we losing?

Heat pump from an air conditioner - how does it work?

To explain how a heat pump from an air conditioner works, we need to have a general understanding of how heat pumps function. Our goal is not to present this concept in an overly technical manner; rather, we aim to discuss it quickly and understandably for laypeople.

✅ A heat pump operates by utilizing a phenomenon that may be unfamiliar to many - it heats water while simultaneously cooling the air outside, where the outdoor unit of the heat pump (or... converted air conditioner) is located. Essentially, it "extracts" heat from the air, even if the outdoor temperature is not very high. This action may seem somewhat contrary to nature and the laws of physics, but not entirely.
☑️ The operation of heat pumps is made possible by the use of special gases - known as refrigerants or, in this case, "freon" (of which there are many different types, and increasingly newer heat pumps utilize its more modern and efficient forms, also more environmentally friendly, etc.). We deliberately use the general term "freon" because the topic is constantly evolving. You may also encounter it referred to as a "refrigerant." You can read more about this topic in another of our articles - specifically about freon.

Freon heats up as it evaporates, with a very low boiling point - interestingly, due to its properties, it can heat up even at low temperatures, even in freezing conditions. This is why heat pumps also operate in subzero temperatures (although they operate less efficiently in these conditions - but they still work, and the freon still heats up). Through the fans of the outdoor unit of the heat pump - or the conversion from the air conditioner - freon continues to heat up, as it can reach even negative temperatures, and this heat is "simply" transferred to our central heating or hot water system.

✅ If we examine the construction of an air conditioner and a heat pump, we'll notice that they are very similarly designed devices. And therein lies the whole key.

Freon or refrigerant - what is it?

In essence, most of us may have heard of freon because it's also used for cooling in refrigerators. Its use in heat pumps or air conditioners is relatively newer. However, in air conditioners or heat pumps, it's often referred to as a "refrigerant" - or by its specific name such as R404, R410a, R407c or more recently R290 and R32.

Heat pump prices - why are they so high?

When compared to the prices of converted air conditioners into heat pumps, yes, heat pump prices are high. However, in this realm, we have professional devices that often come with significantly longer warranty periods. Additionally, they may feature auxiliary heating systems, which help heat the home when temperatures drop below -12 or -15°C, and the heat pump stops producing heat. By the way, these auxiliary heaters (with a power of around 8-10 kW) consume so much electricity that they are a burden for heat pump owners.

✅ Another factor contributing to the high prices of heat pumps is... subsidies for heat pumps.
Yes, regardless of varied opinions on whether governments or international organisations like the EU should support the transition to heat pumps with subsidies, studies have shown that subsidizing such devices by amounts reaching several tens of percent of their value must lead to an increase in their price. Furthermore, artificially stimulating demand always contributes to the increase in the price of a given product, even if it eventually leads to an increase in supply.

In summary, regardless of my sympathy for heat pumps, it's still an expensive technology, sometimes overpriced, and we're still far from the point where it's cost-effective in every household, provided that its residents belong to the middle class. Let's not kid ourselves - demand is also somewhat inflated by political trends motivated by climate change.

Decline in heat pump sales in Europe?

☑️ Recent sales statistics from 2023 and 2024 - according to Bloomberg data - indeed indicate a decrease in the share of heat pumps in the sales of heating devices (analysis across 14 EU countries, including Germany, France, the Netherlands, Denmark, Poland, and the Czech Republic). Has their expansion halted? Or is it merely the influence of slightly less generosity from governments in subsidizing heat pumps? It's hard to say; this is a topic for another article, but price certainly matters. The trend of converting air conditioners into heat pumps surely has a future ahead of it.

Converting an air conditioner into a heat pump - how is it done?

✅ Converting an air conditioner into a heat pump certainly isn't straightforward enough for someone without experience with such devices or at least some basic knowledge of hydraulics to undertake. Nevertheless, individuals with a knack for it often successfully convert air conditioners into inexpensive electric heating systems.

✅ First and foremost, the outdoor unit of the air conditioner must be connected to the central heating system of our home. It will serve as the core of the entire system, producing heat in this way. To do this, we need to use a plate heat exchanger (preferably with thermal insulation), but it must be sensibly chosen; it can't be just any model from an online marketplace. We'll discuss this further below. Additionally, we naturally need a circulation pump to force the circulation. From here, the work becomes increasingly technical - meaning we'll need to configure the automation properly so that the entire heating process operates correctly. This is where professional expertise is required, and we strongly recommend using the services of a company specializing in this field. Unless, of course, someone has the necessary expertise within their circle of acquaintances.

Selecting a heat exchanger for the heat pump converted from an air conditioner - tips

Choosing the right heat exchanger for the heat pump converted from an air conditioner requires attention to several aspects to avoid its leakage - because it's essential to know that freon heated to certain temperatures generates high pressure inside the system, which could rupture the heat exchanger. Therefore:

  • ✔️It must be a high-pressure heat exchanger - one that can work with freon, usually certified for up to 45 bar. It should not be a standard liquid-liquid heat exchanger - as they typically have too low working pressure. In summary, a pressure of 20-30 bar is not sufficient.
  • ✔️It should be a heat exchanger with freon connections in the form of tubes - ready for soldering. This will facilitate our work and speed up the entire conversion process.
  • ✔️The heat exchanger for the heat pump converted from an air conditioner should be selected appropriately in terms of power. It's best to choose it with a certain margin - meaning that the heat exchanger should be able to handle even slightly more power than our air conditioning unit has. +2 kW should be sufficient (of course, we're talking about the power of the heat exchanger calculated for this specific operating mode). That is, for a 5 kW unit, we select a heat exchanger for freon with a minimum power of 7 kW - for certainty.
  • ✔️Alternatively, we can consider checking if the heat exchanger can work with glycol (antifreeze) - if we planned to fill the system with a glycol and water solution to protect it from freezing (for example, if we're doing this in a holiday cottage).

What will happen if the heat exchanger for the air conditioner is too small?

✅ The simple answer is that your heat pump converted from the air conditioner won't work - there's no other way to transfer heat to the system. Alternatively, if the heat exchanger is too small, it will be undersized only to a small extent - it will function, but at half capacity, and there won't be any real benefit from it. Additionally, your heat pump will frequently shut down due to lack of heat transfer, causing the entire system to operate very inefficiently and consume significant amounts of energy.

Professional heat pump vs. DIY heat pump from an air conditioner

✅ In reality, a professional heat pump doesn't differ much from these types of conversions in terms of the basic idea. They are also outdoor units with fans equipped with an appropriate condenser (heat exchanger) transferring heat to a fluid. This is how an air-to-water heat pump works - and if our DIY heat pump converted from an air conditioner is meticulously executed, it's not necessarily unprofessional.

☑️ However, a "professional" heat pump additionally features a range of sensors and automated operation, enriched with modules like Wi-Fi - providing various possibilities for monitoring the performance of the entire system. This is certainly an advantage, sometimes invaluable. It's extremely easy to control - often from our smartphone.

At this point, we must decide whether these advantages are worth the price difference - because the difference in heat production efficiency isn't always significant. Of course, it's assumed that the advantages will always favor professional ready-made solutions, as reputable companies producing heat pumps continually seek new technical solutions to optimize the heating process and reduce energy consumption. We can't expect the same from air conditioners - however, differences in efficiency are not at least striking at the moment.

What air conditioner for a heat pump?

✅ If we want to maximize benefits while maintaining a relatively low price for our home heat pump, and have an efficient and modern system, we should choose what's called an inverter air conditioner. An inverter air conditioner is simply one that can control the compressor's operation through an inverter and adjust the air conditioner's operation to achieve the desired results (i.e., desired temperatures). In other words, an inverter air conditioner will have the ability to modulate power - for example, depending on the needs. An inverter air conditioner will operate "at half capacity" when outside temperature conditions are favorable - saving electrical energy. It will fully utilize its potential when necessary.

An alternative to inverter air conditioning - what else is suitable for a heat pump?

The only alternative is old-fashioned air conditioning without an inverter - thus lacking modulation as well. It will definitely be cheaper - you can buy it for around 2000-2500 PLN - but it won't adjust power to the season's requirements or the building's needs. It's unlikely to be an energy-efficient system.

❌ Converting an air conditioner to HP without an inverter is not a good idea and should be strongly discouraged.

Is it possible to heat the air in a house with an air conditioner - despite converting the AC into an air-to-water heat pump?

✅ Yes, it can be done, but it's a more complex system that requires careful construction and design. Of course, in such a situation, it's important to note that we will also need an indoor unit, which is the air conditioning blower itself. Then, two heat receivers can be connected to the refrigerant circuit in the outdoor unit - namely, the indoor unit (air) and the heat exchanger transferring heat to water. In this case, it's possible to ensure the option of switching the heat receiver - suitable shut-off valves disconnecting the heat exchanger from the installation are sufficient.

Potentially, there's also the possibility of maintaining the option to supply both the blower and the water with heat at the same time. The condition is a sufficiently large outdoor unit of the air conditioner, capable of generating enough heat to supply both heat receivers with thermal energy. The heat exchanger should then be selected so as not to absorb all the power from the air conditioner, but only a part of it - depending on the needs (how much heat we need for our home). However, there's an objective difficulty in correctly calculating this, and it should definitely be done by a specialist.

Do you have to do it yourself?

✅ Definitely not. Converting air conditioners into heat pumps has become somewhat of a trend in our country, and around this issue, a certain economic microclimate has developed, noticed by companies and specialists. Just as you wouldn't install an air conditioner yourself (usually), it's worth looking for offers in this case as well. In addition to being able to buy ready-made converted devices, you can also find companies offering air conditioner conversion to heat pumps practically in every region - along with installation and integration of the system with the boiler room.

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Short glossary of terms related to the topic

AC - commonly used abbreviation for Air-Conditioner or Air-Conditioning

F-gas - fluorinated greenhouse gases, used as refrigerants in air conditioners, refrigerators, freezers, heat pumps (see: freon), they may also appear in the context of the topic, it's worth noting that qualifications are required for their use.

Freon - refrigerant gas used in air conditioning - essentially one of its common names, specialists actually prefer to use the term refrigerant. In reality, freon is a trade name created by some French company that patented it (the word has entered common usage in some languages). It has the ability to absorb heat from the surroundings, even at below-zero temperatures - which is why it's used in air conditioners, heat pumps, and even refrigerators.

Inverter in air conditioning - a device used in newer air conditioners that enables smooth regulation of the compressor's speed, influencing the adjustment of energy consumption and power used to meet the needs.

Inverter air conditioner - a type of air conditioning unit that uses an inverter to regulate the compressor's speed, thereby having the ability to modulate power and energy consumption according to needs. It's definitely more efficient and economical to use, as well as more convenient than older versions without inverters.

Heat pump condenser - a component of the heat pump system that converts the refrigerant from a gaseous (volatile) phase to a liquid phase by transferring heat to another medium or to the surroundings. In our case, we want the heat from the heated refrigerant from the air conditioner to go to water - and into our heating system. Plate heat exchangers are commonly used as condensers in DIY projects.

HP - commonly used abbreviation for Heat Pump

Outdoor AC unit - air conditioning unit located outside the building (in the case of air-to-water devices), equipped with a fan, etc.

Outdoor HC unit - the same as above, but reffering to heat pumps.

Oversizing the heat exchanger / condenser - selecting a heat exchanger designed to operate as a condenser with slightly more power than the power of a given air conditioning unit. This practice is recommended for certainty and to avoid the potential consequences of miscalculations.

Refrigerant - one of the gases used in air conditioners and heat pumps, there are many types such as R404, R407c, R410a, or R32; (see entry: freon)

Refrigerant heat exchanger - a type of heat exchanger, in this case, a plate heat exchanger, with several characteristic features that adapt it for use with refrigerants, cooling agents, etc. The main concern is its resistance to pressures above 40 bar.

R407c, R410a, R404, R290, R32 and similar - the names of specific refrigerant gases used in HP and AC. Of course every one from them has a bit different capacity and parameters. The newest tendency is to replace the older ones with R290 or R32. Especially R32 is considered to be most effective and in the same time has potentially the lowest impact on the environment.

 
Veröffentlicht in: Heat Exchangers, Refrigerants and heat exchangers for gas, Heat pumps and all aspects of their operation

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