Heat Pump & DX Cycle

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1What is a Heat Pump?

2What is a refrigerant DX Cycle?

3Types of systems

4DX system energy efficiency

Why refrigerants?

Heat Pumps are a major contributor to Net Zero target, as it uses natural energy in the ambient air, ground & water, by using electricity4 

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• What is a Heat Pump? 
(Also known as Reverse (heating or cooling) DX Cycle,  or a Vapor Compression Refrigeration System (VCRS).)

Heat Pump is a highly efficent3 sealed DX (Direct Expansion) Cycle2 that comprises of a Compressor, an Evaporator a Condenser and an Expansion Device. It uses refrigerants5 as a circulating media to transfer energy (heat) from outside to inside (heating) or from inside to outside (cooling).

DX Cycle - Heating

Vapor Compression Refrigeration System - (VCRS)

DX Cycle - Cooling

Vapor Compression Refrigeration System - (VCRS)

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 What is a refrigerant DX (Direct Expansion) Cycle?

The refrigerant DX Cycle (also known as Vapor Compression Refrigeration System - VCRS), Is a closed & sealed circuit and has been around for over 200 years. 

The DX cycle utilising refrigerant is used in all types of:

  • Refrigeration systems (mainly Cooling), (industrial, commercial or domestic refrigerators & freezers,)
  • Air conditioning systems (Cooling or Heating / Heat Pump),  (Splits, VRF, Roof Tops, Chillers, AC in cars / trains / ships, etc,

A DX cycle utilising refrigerant can be:

  • Heating only DX cycle transfers Energy [heat] from Outside to Inside
  • Cooling only DX cycle transfer Energy [heat] from Inside to Outside
  • Heating or Cooling DX cycle where a Reversing Valve is incorporated that changes the evaporator to a condenser (heating cycle) or a condenser to an evaporator (cooling cycle), hence the Reverse Cycle terminology

Configeration of Systems:

  • a) Compact (all components in one box) Mono / Roof Top / Chillers, or
    b) Single Splits (one indoor and one outdoor) or
    c) Multi Splits/VRF (multiple indoor units connected to one outdoor unit).

Did you know? In a DX cycle Heat Pump, Heating Capacity is more tha Cooling Capacity?
A: Yes due to the energy (heat) consumed (aprox 80%) by the Compressor, added to the capacity transfered .(see equipment capacity tables)

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Types of systems

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 DX cycle Energy Efficency Advantages due to Refrigerants 

Efficiency of DX cycle = Energy transferred / Energy used by the process

The efficiency of cooling EER- (Energy Efficiency Ratio) cycle or heating cycle COP - (Coefficient Of Performance) can range anything between 250% or (2.5/1) ratio to 500% or (5/1) ratio (that is for every energy unit, [say1 kW] electricity consumed, up to 5 kW can be absorbed from inside (unwanted heat) to be rejected outside - (cooling), or absorbed from outside (air, water or ground) and transferred to inside (heating) to heat a) occupied spaces or b) domestic hot water. These efficiencies (EER & COP) are based on a fixed ambient conditions (called Nominal Capacities).

There are seasonal efficiencies (SEER & SCOP) which are more accurately relates variable ambient conditions and hours of operation.
For example in the UK (considered as mild weather), the SEER can reach 700% or (7/1) ratio while SCOP can be 800% or (8/1) ratio, compared to 85% or (0.85/1) ratio for a gas or oil boilers. Hence a heat pump is a "major contributor to Net Zero target"

The Indoor units can be a Wall, Floor, Ceiling or Ducted fan coils or a refrigerant to water heat exchanger (to provide domestic hot water) or medium temperature heating water for under floor heating, radiators of water fan coils. The interconnecting refrigeration pipe work would require specialist approved refrigeration engineers and materials. 

Advantages of DX cycle Heat Pump heating/hotwater systems over fossile fuel systen (Natural Gas or Oil or Coal):

a) No extra safety systems - Gas detectors, fire/smoke alarm, extra ventilation (provided the refrigerant is A1 class non-flammable),
b) No chimneys,hence no local pollution
c) No Natural Gas supply,
d) No fuel storage (oil),
e) Less builder’s work,
f) Normal electrical supplies (domestic).
g) No network (gas) installation, maintenance, repair or fire safety
h) No supply (oil, gas in rural areas or coal) logistics & costs
i) No import or supply security risks associated with imports of fossil fuels.

Location of outdoor units can be as far as 100 meters away from indoor units in an Air to Air split systems. 

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 Why refrigerant?





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