A bright future for heat pumps

By Ilana Koegelenberg

As the global heat pump market grows alongside the rising demand for energy-efficient buildings globally, we take a look at exactly what a heat pump is in terms of HVAC&R and how to look after a heat pump.

Heat pumps have always been a topic of much confusion for me. Well, not exactly ‘always’. The first feature I ever did on ‘heat pumps’ was for our sister publication Plumbing Africa, talking about how these new and innovative water heaters were negating the need for energy-hungry geysers. Needless to say, I thought I knew what a ‘heat pump’ was and advocated its impressive efficiencies far and wide, to the extent that my father even installed a couple at his business.

HP001How does a geothermal heat pump work?
Image credit: tidewatermechanical.com

Then came the time to tackle the topic of ‘heat pumps’ for RACA Journal and I quickly (not quickly enough) learnt that these were two completely different things. I was not the only one who was confused, though. Many interviews later, with half the info I had collected actually being on water heat pumps instead of HVAC heat pumps, I was in a desperate state. Charles Nicolson, our technical subeditor and long-time safety net, helped me fix the article to a point where at least it was somewhat logical, but it was far from being something to be proud of.  

When I saw the dreaded ‘heat pump’ feature on my list again for this edition, I was not about to hit my head against the same rock. So, I tried my luck and reached out to the ASHRAE Journal publishers — always my first port of call in terms of readily available world-class content. But unfortunately, they could not help me out either. According to Jay Scott, editor of the ASHRAE Journal, although a heat pump feature was on the cards for 2018, they haven’t really done anything on heat pumps in the past two years. Back to the drawing board.

After some ‘research’ (read: ‘enlisting my good friend Google’), I tracked down a very informative article that explained the different kinds of heat pumps very simply and in an easy-to-understand manner. It was produced by the US Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE), who were surprisingly quick to get back to me and let me know that they were more than happy for me to use any info from the article.

So here it is, once and for all: an informative guide on the HVAC&R heat pump and a glance at the market at large, both locally and abroad.

WHAT IS A HEAT PUMP?

For climates with moderate heating and cooling needs, heat pumps offer an energy-efficient alternative to furnaces and air conditioners. Like your refrigerator, heat pumps use electricity to move heat from a cool space to a warm space, making the cool space cooler and the warm space warmer. During the heating season, heat pumps move heat from the cool outdoors into the warm building and during the cooling season, heat pumps move heat from the cool building into the warm outdoors. Because they move heat rather than generate heat, heat pumps can provide equivalent space conditioning at as little as one-quarter of the cost of operating conventional heating or cooling appliances.

HP003A heat pump can provide an alternative to using an air conditioner.
Image credit: iStockPhoto

There generally are three types of heat pumps: air-to-air, water source, and geothermal. They collect heat from the air, water, or ground outside a building and concentrate it for use inside.

The most common type of heat pump is the air-source heat pump, which transfers heat between a building and the outside air. Today’s heat pump can reduce electricity use for heating by approximately 50% compared to electric resistance heating options. High-efficiency heat pumps also dehumidify better than standard central air conditioners, resulting in less energy usage and more cooling comfort in summer months.

For buildings without ducts, air-source heat pumps are also available in a ductless version called a mini-split heat pump. In addition, a special type of air-source heat pump called a ‘reverse cycle chiller’ generates hot and cold water rather than air, allowing it to be used with radiant floor heating systems in heating mode.

Geothermal (ground-source or water-source) heat pumps achieve higher efficiencies by transferring heat between the building and the ground or a nearby water source. Although they cost more to install, geothermal heat pumps have low operating costs because they take advantage of relatively constant ground or water temperatures.

Geothermal heat pumps have some major advantages. They can reduce energy use by 30–60%, control humidity, are sturdy and reliable, and fit in a wide variety of buildings. Whether a geothermal heat pump is appropriate for a project will depend on the size of the development, the subsoil, and the landscape. Ground-source or water-source heat pumps can be used in more extreme climates than air-source heat pumps, and customer satisfaction with the systems is very high.

A new type of heat pump, especially for residential systems, is the absorption heat pump, also called a gas-fired heat pump. Absorption heat pumps use heat as their energy source, and can be driven with a wide variety of heat sources.

AIR-SOURCE HEAT PUMPS 

A heat pump’s refrigeration system consists of a compressor and two coils made of copper tubing (one indoors and one outside), which are surrounded by aluminium fins to aid heat transfer. In heating mode, liquid refrigerant in the outside coils extracts heat from the air and evaporates into a gas. The indoor coils release heat from the refrigerant as it condenses back into a liquid. A reversing valve, near the compressor, can change the direction of the refrigerant flow for cooling as well as for defrosting the outdoor coils in winter.

HP002 A basic heat pump configuration.
Image credit: energy-alaska.wikidot.com

The efficiency and performance of today’s air-source heat pumps is a result of technical advances such as the following:

  • Thermostatic expansion valves for more precise control of the refrigerant flow to the indoor coil.
  • Variable speed blowers, which are more efficient and can compensate for some of the adverse effects of restricted ducts, dirty filters, and dirty coils.
  • Improved coil design.
  • Improved electric motor and two-speed compressor designs
  • Copper tubing, grooved inside to increase surface area.

One of the more notable innovations in air-source heat pumps is called a reverse cycle chiller (RCC). It offers the advantages of allowing the homeowner to choose from a wide variety of heating and cooling distribution systems, from radiant floor systems to forced air systems with multiple zones. It also offers the potential for lower winter electricity bills and hotter air out of the supply vents for greater comfort.

The different types of air-source heat pumps are described below.

Ductless vs ducted vs short-run ducted: Ductless applications require minimal construction, as only a small hole through the wall is required to connect the outdoor condenser and the indoor heads. Ductless systems are often installed in additions. Ducted systems simply use ductwork. If the building already has a ventilation system or is a new build, this system is worth considering. Short-run ducted is traditional large ductwork that only runs through a small section of the building. Short-run ducted is often complemented by other ductless units for the remainder of the building.

Split vs packaged: Most heat pumps are split-systems — that is, they have one coil inside and one outside. Supply and return ducts connect to the indoor central fan. Packaged systems usually have both coils and the fan outdoors. Heated or cooled air is delivered to the interior from ductwork that passes through a wall or roof.

Multi-zone vs single-zone: Single-zone systems are designed for a single room with one outdoor condenser matched to one indoor head. Multi-zone installations can have two or more indoor heads connected to one outdoor condenser. Multi-zone indoor heads vary by size and style and each creates its own ‘zone’ of comfort, allowing you to heat or cool individual rooms, hallways, and open spaces. This distinction may also be referred to as ‘multi-head vs single-head’ and ‘multi-port vs single-port’.


Because they move heat rather than generate heat, heat pumps can provide equivalent space conditioning at as little as one-quarter of the cost of operating conventional heating or cooling appliances.


GEOTHERMAL HEAT PUMPS

Geothermal heat pumps (GHPs), sometimes referred to as earth-coupled, ground-source, or water-source heat pumps, have been in use internationally since the late 1940s. They use the constant temperature of the earth as the exchange medium instead of the outside air temperature.

Although many parts of the country experience seasonal temperature extremes — from scorching heat in the summer to sub-zero cold in the winter — a few metres below the earth’s surface, the ground remains at a relatively constant temperature. Depending on latitude, ground temperatures range from 7°C to 21°C. Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of this by exchanging heat with the earth through a ground heat exchanger.

As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the hot water. Some models of geothermal systems are available with two-speed compressors and variable fans for more comfort and energy savings. Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.

A dual-source heat pump combines an air-source heat pump with a geothermal heat pump. These appliances combine the best of both systems. Dual-source heat pumps have higher efficiency ratings than air-source units, but are not as efficient as geothermal units. The main advantage of dual-source systems is that they cost much less to install than a single geothermal unit, and work almost as well.

Even though the installation price of a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, the additional costs are returned in energy savings in five to 10 years. System life is estimated at 25 years for the inside components and 50+ years for the ground loop.

There are four basic types of ground loop systems. Three of these — horizontal, vertical, and pond/lake — are closed-loop systems. The fourth type of system is the open-loop option. Which one of these is best depends on the climate, soil conditions, available land, and local installation costs at the site. All of these approaches can be used for residential and commercial building applications.

Closed-loop systems: Most closed-loop geothermal heat pumps circulate an antifreeze solution through a closed loop — usually made of plastic tubing — that is buried in the ground or submerged in water. A heat exchanger transfers heat between the refrigerant in the heat pump and the antifreeze solution in the closed loop. The loop can be in a horizontal, vertical, or pond/lake configuration.

HP004A heat pump is a very efficient way to heat and cool any building.
Image credit: Danfoss

Open-loop system: This type of system uses well or surface body water as the heat exchange fluid that circulates directly through the GHP system. Once it has circulated through the system, the water returns to the ground through the well, a recharge well, or surface discharge. This option is obviously practical only where there is an adequate supply of relatively clean water, and all local codes and regulations regarding groundwater discharge are met.

<bold> Hybrid systems using several different geothermal resources, or a combination of a geothermal resource with outdoor air (that is, a cooling tower), are other technology options. Hybrid approaches are particularly effective where cooling needs are significantly larger than heating needs.

ADVANCED FEATURES

There are a number of innovations that are improving the performance of heat pumps.

Unlike standard compressors that can only operate at full capacity, two-speed compressors allow heat pumps to operate close to the heating or cooling capacity needed at any particular moment. This saves large amounts of electrical energy and reduces compressor wear. Two-speed heat pumps also work well with zone control systems. Zone control systems, often found in larger buildings, use automatic dampers to allow the heat pump to keep different rooms at different temperatures.

Some models of heat pumps are equipped with variable-speed or dual-speed motors on their indoor fans (blowers), outdoor fans, or both. The variable-speed controls for these fans attempt to keep the air moving at a comfortable velocity, minimising cool drafts and maximising electrical savings while also minimising the noise from blowers running at full speed.

Many high-efficiency heat pumps are equipped with a desuperheater, which recovers waste heat from the heat pump’s cooling mode and uses it to heat water. A desuperheater-equipped heat pump can heat water two to three times more efficiently than an ordinary electric water heater.

Another advance in heat pump technology is the scroll compressor, which consists of two spiral-shaped scrolls. One remains stationary, while the other orbits around it, compressing the refrigerant by forcing it into increasingly smaller areas. Compared to the typical piston compressors, scroll compressors have a longer operating life and are quieter. According to some reports, heat pumps with scroll compressors provide 5.6° to 8.3°C warmer air when in heating mode, compared to existing heat pumps with piston compressors.


Air-to-water is the dominating segment and accounts for a major share in the overall industry in 2016. The segment is set to witness significant growth owing to its increasing applications. 


MAINTENANCE AND OPERATION

Like all heating and cooling systems, proper maintenance is key to efficient operation. The difference between the energy consumption of a well-maintained heat pump and a severely neglected one ranges from 10% to 25%.

Clean or change filters once a month or as needed, and maintain the system according to manufacturer’s instructions. Dirty filters, coils, and fans reduce airflow through the system. Reduced airflow decreases system performance and can damage the system’s compressor. Clean outdoor coils whenever they appear dirty; occasionally, turn off power to the fan and clean it; remove vegetation and clutter from around the outdoor unit.

A professional technician should service the heat pump at least every year. The technician can do the following:

  • Inspect ducts, filters, blower, and indoor coil for dirt and other obstructions.
  • Diagnose and seal duct leakage.
  • Verify adequate airflow by measurement.
  • Verify correct refrigerant charge by measurement.
  • Check for refrigerant leaks.
  • Inspect electric terminals, and, if necessary, clean and tighten connections, and apply nonconductive coating.
  • Lubricate motors, and inspect belts for tightness and wear.
  • Verify correct electric control, making sure that heating is locked out when the thermostat calls for cooling and vice versa.
  • Verify correct thermostat operation.

THE GLOBAL MARKET

According to the Building Services Research and Information Association (BSRIA), the 2016 global air-to-water (ATW) heat pump market was valued at USD4.117-million. This represents an increase of 24% from the previous year. In volume terms, heat pump suppliers sold almost three million units across the globe. China is the engine of this growth, with 2.5 million ATW heat pump units sold in 2016. In Europe, the sales of ATW heat pumps went up 6.3% to 405 000 units, following the 13% growth recorded in 2015. France continues to lead the European market for ATW heat pumps with 168 000 units sold.

Shifting consumer preference towards eco-friendly and ‘green’ technology is estimated to surge the business growth in the heat pump market, according to the Heat Pumps Market Share – Industry Size Report 2017-2024 recently released by Global Market Insights. Extensive R&D along with technological innovations in the energy-efficient equipment will fuel the product development. Depletion of conventional energy sources and petroleum reserves, accompanied by growing energy demand and regulatory compliance, will create new avenues for heat pumps market growth.

High initial costs and low consumer consciousness about fuel-efficient substitutes are major restraining factors of the industry demand. Lack of government compliance in some regions is a major factor impacting the industry growth. Technical installation complications in existing structures may hamper the heat pumps market.

The heat pumps market is further segmented based on product as geothermal, air-to-air, and air-to-water pumps. Air-to-water is the dominating segment and accounts for a major share in the overall industry in 2016. The segment is set to witness significant growth owing to its increasing applications.

The geothermal heat pumps market is estimated to surpass USD130 billion up to 2024. Superior comfort and silent operation are the key properties driving the product demand. Geothermal products have relatively superior efficiency due to thermal exchange from ground that is at stable temperature. The segment will witness stagnant growth owing to decreasing demand particularly in Europe.

HP005Most split units we see in buildings today are in fact what is termed a ‘heat pump’.
Image credit: www.airconspecialists.co.nz

Rising demand for natural or low global warming potential refrigerants will drive the heat pumps market. Refrigerants are used in open or closed cycle and act as an intermediate medium for thermal exchange. Ammonia and CO2 refrigerant-based heat pumps have witnessed increasing demand in recent years.

Enhanced efficiency in residential applications, coupled with rapid adoption in Europe and Japan due to environment-friendly properties will propel the revenue growth from the CO2-based heat pumps market. Moreover, inclination towards eco-friendly products and rising global warming awareness will trigger the demand.

Europe dominates the global industry share and is expected to remain dominant. As per the European Heat Pump Association (EHPA), increasing heat pump usage will reduce overall energy imports. EU annual expenditure on energy imports is worth over USD420 billion. The region held more than seven million operating products in 2014. Shifting preference for renewable energy sources will drive the regional demand. Increasing product usage in Germany, Sweden, Italy, France, Finland, and Norway has accounted for over 80% of the renewable energy production.

The Asia Pacific heat pumps market is set to witness the fastest growth in the forecast timeframe. Growing construction accompanied by favourable regulatory policies on energy efficiency particularly in Japan, India and China, will fuel the regional demand. Rising demand from the residential segment owing to increasing infrastructure development has enhanced the product development in this region.

The global heat pumps market share is highly competitive with many players. Who will come out on top remains to be seen …

REFERENCES

  • US Department of Energy. Read more
  • Heat Pumps Market Share – Industry Size Report 2017–2024

Click below to read the January 2018 issue of RACA Journal

RACA JAN2018

 

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