The role of industrial heat pumps in District Energy

District energy may not be the most common source of heating and cooling globally, but it is a growing technology that is widely implemented in places like Northern Europe and North America. One of the most significant developments in district energy over the last few decades has been the improvement of heat pumps.

Heat pumps are now becoming central to both commercial and residential sectors in some countries. As an example, Europe’s 2020 energy targets partly depend on this technology. Moreover, currently heat pumps are considered as renewable energy always that the performance reaches a minimum value (Seasonal Performance Factor of the system must exceed 2.5).

In the industrial sector, savings in energy consumption and CO2 emissions are ever important. The use of waste heat reduces both the energy consumption and green-house gases emissions so it is gaining momentum, and with this trend comes focus on industrial heat pumps. Just what are these devices all about? How well do they fit in the industrial environment?

 

How a heat pump works

Conventionally, property owners cool and heat their properties using air conditioners and heaters respectively. A heat pump system is a replacement of both air conditioner and heater because it can provide cooling and heating.

How does it achieve this? Essentially, this equipment is a heat transporter. It operates in two modes: cooling and heating.

  • In the heating mode, the pump draws heat from the outside environment to an enclosed space.
  • In the cooling mode, it transfers heat to the outside environment, hence behaving like an air conditioner.

District Energy reference book

 

Two refrigeration cycles

A heat pump can use either the absorption cycle or the vapor compression cycle. Absorption cycle heat pumps are driven by thermal energy. Those used for heating in residential or commercial buildings rely on gas while the industrial heat pumps normally use waste heat or high-pressure steam. The mainstay of absorption cycle heat pumps is the water-absorbing characteristic of salt or liquids. It uses absorbent and working fluid combinations with common pairings being:

  • Water and ammonia
  • Lithium bromide and water

The working fluid undergoes compression in a solution circuit that comprises of expansion valve, solvent pump, absorber and thermal compressor.

In the vapor compression cycle varieties, there are four main components namely condenser, compressor, expansion valve and evaporator. A refrigerant goes through these components as shown in Figure 1.

The vapor-compression heat pump is the more popular of the two. It is often what people mean when they talk about a heat pump. This technology has been around for a long time.

Fig 1: Schematic Representation of a Heat Pump Cycle

As shown in the figure above, the refrigerant evaporates when it comes in contact with a heat source in the evaporator, cooling down the heat source (e.g. water for district cooling). The gaseous refrigerant goes to the compressor, where it changes to a vapor under high pressure and temperature. Thereafter, the fluid undergoes condensation to exchange the heat with the cold source, which is heated up (e.g. water for district heating). It then expands in the expansion valve and the cycle starts again.

 

Application of heat pumps in District Energy

As aforementioned, heat pumps are used in many segments of the industry, residential and commercial markets. Some industrial applications include food processing, automobile, cold stores, pharmaceutical and dairy sectors. Moreover, they are used for process cooling, air conditioning and process heating among others.

For residential and commercial applications, you can find heat pumps in households, hotels, hospitals and health clubs where they offer sanitation, water heating, water-cooling and air conditioning. But, why are heat pump systems from ARANER popular for these applications?

 

Energy efficiency

First, the preference of heat pumps in district energy has to do with the fact that this technology is very energy efficient. Most industries are striving to keep energy consumption as low as possible, which is understandable given the rising energy costs.

A heat pump from ARANER offers an energy efficient option for these cases. It is important to notice that in case the clients wants to use both heating and cooling at the same time, the heating and cooling demands need to be balanced for the best results with these devices. In case the gap between these demands is wide, a Thermal Energy Storage (TES) tank comes in handy.

 

Enhanced safety

What is the safety standing of a heat pump for heating compared to an alternative source, say furnace? Unlike furnaces, with heat pumps there is no worry of hot flames or surfaces. Furthermore, there are no carbon dioxide leaks to give the maintenance team sleepless nights. ARANER uses ammonia (a natural refrigerant) because of its desirable thermodynamic characteristics. Most clients have stringent environmental demands, but this refrigerant ensures compliance in most cases. Other than ammonia, the designers may also use R410a or R134a.

Other advantages of an ARANER industrial heat pump are:

  • Low maintenance costs
  • Design suitable for Green Building (LEED) certification
  • Natural refrigerants are applicable
  • Same equipment used for both heating and cooling

Has the industry wholly embraced the idea of heat pumps in district energy? Maybe not and there is a reason behind this. Industrial heat pumps for district energy may be expensive ventures if added to existing networks. Most heat pumps are only used in satellite applications. However, they can reduce running costs significantly if used together with CHP systems.

For economic analysis and other design considerations of an industrial heat pump installation, contact industrial energy experts at ARANER.

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