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MelPump: Heat Pump Guide

Your complete guide to understanding heat pumps

school What is a Heat Pump?

A heat pump is a highly efficient device that transfers heat from one place to another. Instead of generating heat directly (like a gas boiler), it moves existing heat from outside air or ground into your home.

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Did you know? Heat pumps can produce 3-5 times more heat energy than the electrical energy they consume. This makes them one of the most efficient heating systems available.

Types of Heat Pumps

air Air Source (ASHP)

Extracts heat from outside air. Most common type, easier to install. Works even when outdoor temperature is below zero.

landscape Ground Source (GSHP)

Extracts heat from the ground via buried pipes (brine circuit). More efficient but requires more installation work.

How Does It Work?

A heat pump works like a refrigerator in reverse. Here's the simplified process:

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1. Absorb

Refrigerant absorbs heat from outside

compress

2. Compress

Compressor increases temperature

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3. Release

Heat released to your home

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4. Repeat

Cycle continues automatically

remove_circle add_circle Show more technical details

The refrigeration cycle consists of four main components:

Evaporator - Located in outdoor unit, absorbs heat from air/ground
Compressor - The heart of the system, increases refrigerant pressure and temperature
Condenser - Releases heat to your heating water
Expansion valve - Reduces pressure before the cycle repeats

warning The compressor is the most expensive component. Protecting it from frequent starts/stops (short cycling) is essential for longevity.

tune Operation Modes

Your heat pump can operate in different modes depending on current heating or cooling needs:

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Heating

Heat is extracted from outside and transferred into your home. Used during cold months.

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Cooling

Cycle reverses - heat is removed from inside and released outside. Used during warm months.

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Hot Water

Heat pump heats domestic hot water in the storage tank. Can work alongside space heating.

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Idle / Standby

Target temperature reached. Compressor is off, system monitors temperatures.

error Watch Out: Short Cycling

If your heat pump frequently switches between modes or turns on/off every few minutes, this is called "short cycling". It can seriously damage the compressor over time.

Healthy operation: Long, continuous cycles (30+ minutes) with gradual frequency changes. Avoid frequent compressor stops.

remove_circle add_circle What are heating zones?

Many installations have two separate heating zones that can be controlled independently:

Zone 1 - Usually the main heating circuit (e.g., underfloor heating or main radiators)
Zone 2 - Secondary circuit (e.g., upstairs radiators or a different building section)

thermometer Temperature Readings

Understanding temperature readings is key to monitoring your heat pump's performance. Here's what each measurement means:

Water temperature leaving the heat pump and going into the heating system. This is the "output" of your heat pump.

Typical values:

Underfloor heating: 30-40°C
Radiators: 45-55°C

warning Efficiency tip: Lower flow temperature = higher efficiency. Every degree lower saves energy. Use the lowest temperature that keeps your home comfortable.

Water temperature returning to the heat pump after circulating through your heating system. Should be lower than flow temperature.

What to look for: Should be 3-7°C lower than flow temperature.

The difference between flow and return temperatures. Shows how much heat is being transferred to your home.

Ideal values:

Underfloor heating: ~5°C
Radiators: 7-10°C

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Problem signs:

ΔT too small (1-2°C): Water pump may be running too fast, or system not absorbing heat properly
ΔT too large (>12°C): Flow may be restricted - check for blockages, air in system, or pump issues

Outside air temperature measured by the outdoor unit. Used for weather-compensated heating curves.

lightbulb The colder it is outside, the harder the heat pump works and efficiency (COP) decreases. This is normal - extracting heat from very cold air requires more energy.

Current temperature of domestic hot water in the storage tank.

Typical settings:

Daily use: 45-50°C
Legionella prevention: 60°C+ (periodic)

Internal temperature where refrigerant releases heat to the water system. Higher values usually indicate the system is working harder.

warning Very high condensing temperatures reduce efficiency. If consistently high, check if flow temperature can be lowered.

For ground source heat pumps - temperature of fluid in the ground loop entering and leaving the heat pump.

Brine Inlet - Fluid returning from ground (warmer in winter)
Brine Outlet - Fluid going to ground (cooler after heat extracted)

error If brine inlet regularly drops below 0°C, the ground loop may be undersized or there's a problem with the collector.

settings Compressor & Frequency

The compressor is the heart of your heat pump - and also its most expensive component. Understanding how it works helps you optimize settings and extend its lifespan.

Compressor Frequency

Modern heat pumps use inverter compressors that run at variable speeds. The frequency (Hz) indicates how hard the compressor is working:

20-40 Hz

Low demand

Efficient operation, maintaining temperature

40-70 Hz

Medium demand

Normal operation, actively heating

70-120 Hz

High demand

Maximum output, cold weather or recovery

dangerous Short Cycling - The Compressor Killer

Short cycling occurs when the compressor starts and stops frequently (multiple times per hour). This is extremely harmful because:

Each start causes mechanical stress and electrical surge
Startup phase uses more energy than continuous running
Oil doesn't circulate properly in short cycles
Can lead to premature compressor failure

Solutions: Add or enlarge buffer tank, lower target temperatures, adjust heating curve, ensure system is properly sized.

Flow Rate

The flow rate (liters/minute) shows how much water circulates through the system. This is crucial for heat transfer:

Too Low

Heat pump may overheat and shut down. Poor heat distribution throughout the house.

Too High

Delta T becomes too small. Wasted pump energy without efficiency benefit.

Dropping Over Time

May indicate clogged filter, air in system, or water pump degradation.

remove_circle add_circle Other compressor-related parameters

Fan RPM - Speed of outdoor unit fans. Varies with heating demand and defrost needs.
LEV (Expansion Valve) - Controls refrigerant flow. Position changes based on operating conditions.
Water Pump Status - Whether internal circulation pump is running.
3-Way Valve - Directs flow between heating circuit and hot water tank.

eco Efficiency & COP

What is COP?

COP (Coefficient of Performance) measures how efficient your heat pump is. It's the ratio of heat output to electrical input.

COP = Heat Output ÷ Electrical Input

Example: COP of 4 means for every 1 kWh of electricity, you get 4 kWh of heat

What Affects COP?

arrow_upward Higher COP (Better)

Lower flow temperatures
Warmer outdoor temperatures
Underfloor heating systems
Properly sized heat pump
Good insulation

arrow_downward Lower COP (Worse)

Higher flow temperatures
Very cold outdoor conditions
Frequent defrost cycles
Booster heater usage
Oversized or undersized system

Energy Consumed vs Produced

The app shows estimated input power (electricity) and output power (heat). Monitoring these helps you understand real-world efficiency:

Estimated Input Power - Electricity being consumed by the heat pump
Estimated Output Power - Heat being delivered to your home
Estimated COP - Real-time efficiency (Output ÷ Input)

show_chart Track your energy over time to spot trends. A sudden drop in efficiency might indicate a problem needing attention, such as low refrigerant, dirty filters, or sensor issues.

ac_unit Defrost & Booster Heaters

Defrost Mode

In cold, humid conditions, frost builds up on the outdoor unit's heat exchanger. The heat pump periodically runs defrost cycles to remove this ice.

info How Defrost Works

During defrost, the heat pump temporarily reverses - it takes heat from inside your home to melt ice on the outdoor unit. You may notice a brief drop in heating during this time. This is normal.

warning When to Be Concerned

Defrost cycles lasting more than 10-15 minutes
Defrost happening more than 2-3 times per hour in extreme cold
Ice that doesn't clear after defrost
Defrost running when outdoor temperature is above 5°C

Booster Heaters

Heat pumps include electric backup heaters for situations when the compressor alone cannot meet demand:

Booster Heater 1 & 2 - Electric elements in the hydrobox that help heat water
Immersion Heater - Electric element in the hot water tank

bolt Warning: High Energy Cost

Electric backup heaters have COP of 1 - they produce only 1 kWh of heat per 1 kWh of electricity. This is 3-5x less efficient than the heat pump compressor.

Monitor for: If booster heaters run frequently during normal weather, your system may be undersized or settings need adjustment.

Legionella Mode

Periodically heats the hot water tank to 60°C+ to kill Legionella bacteria. This often requires booster heaters since heat pumps are most efficient at lower temperatures.

shield Legionella cycles are important for health safety but are energy-intensive. Most systems run them weekly. Consider scheduling during off-peak electricity hours.

list_alt All Parameters Reference

Below is a complete list of parameters available in the app. Note that not all parameters apply to every heat pump.

info Availability depends on your specific model, installation type (air source vs ground source), and whether you have additional sensors or the WiFi adapter installed.

remove_circle add_circle Click to expand full parameter list

Parameter	Description
`Compressor Status`	Shows whether the compressor is currently running or idle
`Compressor Frequency`	Speed of the compressor in Hz, higher values mean more heating or cooling power
`Defrost Mode`	Indicates when the outdoor unit is melting ice buildup
`Power`	Whether the heat pump is turned on or off
`Booster Heater 1 Status`	Shows if the first backup electric heater is active
`Booster Heater 2 Status`	Shows if the second backup electric heater is active
`Booster Heater 3 Status`	Shows if the third backup electric heater is active
`Immersion Heater Status`	Shows if the electric heater inside the hot water tank is active
`Operation Mode`	Current mode: heating, cooling, or hot water production. May also show other modes like antifreeze or legionella.
`Operation Mode #1`	Operating mode for heating zone #1. In most heat pumps this is either constant flow or compensation curve mode, but some models may support advanced modes like auto-adaptation.
`Operation Mode #2`	Operating mode for heating zone #2. In most heat pumps this is either constant flow or compensation curve mode, but some models may support advanced modes like auto-adaptation.
`Has Error`	Indicates if the system has an active error
`Error Code`	Diagnostic code shown when there is a problem
`Zone 1 Active`	Whether heating/cooling zone #1 is currently active
`Zone 2 Active`	Whether heating/cooling zone #2 is currently active
`Flow Rate`	Amount of water flowing through the system in litres per minute
`Fan 1 RPM`	Speed of the first outdoor unit fan
`Fan 2 RPM`	Speed of the second outdoor unit fan
`Lev A`	Electronic expansion valve opening position
`Input Power`	Estimated electrical power being consumed
`Output Power`	Estimated heat energy being produced
`COP`	Efficiency ratio - heat output divided by electricity input
`Water Pump 1 Status`	Shows if the water circulation pump is running
`Water Pump 2 Status`	WaterPump2Status
`Water Pump 3 Status`	WaterPump3Status
`Water Pump 4 Status`	WaterPump4Status
`3-Way Valve Status`	Position of valve directing water to heating or hot water tank
`Max Tank Water Temperature`	Maximum allowed hot water tank temperature setting
`Force Hot Water`	Forces immediate hot water heating regardless of schedule
`Prohibit Heating Zone #1`	When enabled, prevents heating in zone #1
`Prohibit Heating Zone #2`	When enabled, prevents heating in zone #2
`Prohibit Heating Hot Water`	When enabled, prevents hot water heating
`Prohibit Cooling Zone #1`	When enabled, prevents cooling in zone #1
`Prohibit Cooling Zone #2`	When enabled, prevents cooling in zone #2
`Holiday mode`	Reduced operation mode to save energy during vacations
`Eco Hot Water`	Energy-saving mode that heats water more slowly using lower flow temperatures for better efficiency
`MEL Pump App Control Mode`	Whether the system is controlled via the server, supported only by Mitsubishi heat pumps
`Service Code`	Diagnostic code used by service technicians to get heat pump parameter details
`Indoor Temp #1`	Current air temperature in rooms served by heating zone #1
`Indoor Temp #2`	Current air temperature in rooms served by heating zone #2
`Outdoor Temp`	Current outside air temperature measured near the heat pump
`Flow Temp`	Water temperature leaving the heat pump and going into the heating system
`Return Temp`	Water temperature returning to the heat pump from the heating system
`Flow Temp #1`	Water temperature supplied to heating zone #1
`Return Temp #1`	Water temperature returning from heating zone #1
`Flow Temp #2`	Water temperature supplied to heating zone #2
`Return Temp #2`	Water temperature returning from heating zone #2
`Thermostat Temp #1`	Desired room temperature set for heating zone #1
`Target Temp #1`	Target water temperature for the heating circuit in zone #1
`Thermostat Temp #2`	Desired room temperature set for heating zone #2
`Target Temp #2`	Target water temperature for the heating circuit in zone #2
`Delta Temp`	Difference between the water leaving and returning to the heat pump, used to show how much heat is being transferred
`Tank Water Temp`	Current temperature of the domestic hot water stored in the tank
`Condensing Temp`	Internal heat pump temperature where refrigerant releases heat to the water system, higher values usually mean lower efficiency
`Target Tank Water Temp`	Desired domestic hot water tank temperature
`Flow Temp Boiler`	Water temperature leaving the backup boiler
`Return Temp Boiler`	Water temperature returning to the backup boiler
`Mixing Tank Water Temp`	Water temperature inside the buffer or mixing tank
`Brine Inlet Temp`	Temperature of the ground loop fluid entering the heat pump
`Brine Outlet Temp`	Temperature of the ground loop fluid leaving the heat pump
`Liquid Line Temp`	Temperature of the liquid refrigerant flowing through the heat pump's cooling circuit

warning Troubleshooting

Here are some common issues and what to check:

Check if flow temperature is appropriate for your heating system
Verify heating curve settings match your home's heat loss
Check for air in the system (radiators may need bleeding)
Ensure all zone valves are opening correctly
Check if heat pump is undersized for your home

Check how often booster heaters are running - they use a lot of electricity
Review COP values - if consistently below 2.5, investigate
Look for excessive defrost cycles
Consider if flow temperatures can be reduced
Check Legionella cycle frequency and timing

This is short cycling - needs attention to protect compressor
Consider adding or enlarging buffer tank
Reduce target temperatures or adjust heating curve
Check if system is oversized for your heat demand
Ensure minimum flow rate is maintained

Check if hot water mode is enabled
Verify 3-way valve is switching to tank position
Check if immersion heater is working (if equipped)
Review hot water schedule settings
Tank sensor may need checking

Check and clean the system filter
Bleed air from the system
Check water pump operation
Inspect for blockages in pipes
Check system pressure

Check if the integration is active
If you added the integration using a guest account, check if you have granted all required permissions
Check that your heat pump controller is on the main screen - some heat pumps don't send data if you open a submenu and leave it there
After returning to the main screen on the controller, you may need to wait up to 24 hours for data to start flowing again
Check if there is data in the original manufacturer app - if not, your heat pump may not support this feature or may have a sensor misconfiguration

Ready to Monitor Your Heat Pump?

Start tracking all these parameters and optimize your heat pump's performance. Join thousands of users who are saving energy and extending their heat pump's lifespan.