Guide to Using the Air-to-Air Heat Pump Calculator

Introduction

1.1 What is an Air-to-Air Heat Pump?

An air-to-air heat pump (also called split air conditioning) is a highly efficient heating and cooling system that extracts heat from outdoor air and delivers it directly to indoor air. Unlike air-to-water heat pumps, it operates without a water circuit and can therefore be installed particularly quickly and flexibly.

Structure of a Split System:

• Outdoor unit: Contains compressor and heat exchanger, extracts heat from outdoor air
• Indoor unit(s): Deliver heat to the room (or extract heat in cooling mode)
• Refrigerant lines: Connect outdoor and indoor unit(s)

1.2 Single-Split vs. Multi-Split

Single-Split Advantages:

• Simpler installation
• Lower acquisition cost
• Independent operation

Multi-Split Advantages:

• One outdoor unit for multiple rooms
• Less outdoor space required
• Central control possible

1.3 Comparison with Air-to-Water Heat Pumps

1.4 Typical Use Cases

1. Supplement to Existing Heating (Bivalent Operation)

• Air-to-air HP covers base load during transition periods
• Existing heating kicks in at low temperatures
• 30-60% heating cost savings possible

2. Single Room Full Coverage

• Living room, home office, conservatory
• Quick heat without warming entire heating system
• Cooling in summer

3. Summer Cooling

• Primary use as air conditioner
• Heating function as additional benefit

4. PV Self-Consumption Optimization

• Excess solar power for heating/cooling
• Particularly attractive in summer (cooling at PV peak)

1.5 Regulatory Basis

This calculator is based on:

• EN 14825:2022: Calculation of SCOP (heating) and SEER (cooling)
• VDI 4650: Seasonal performance factor for heat pumps
• EN 14511: Performance measurement at rated conditions

Calculation Fundamentals

2.1 SCOP - Seasonal Heating Efficiency

The SCOP (Seasonal Coefficient of Performance) is the most important metric for heating efficiency. It indicates how much heat is generated per kilowatt-hour of electricity consumed on an annual average.

Formula:

SCOP = Annual heating output [kWh] / Annual electricity consumption [kWh]

Example: SCOP = 4.2 means: 4.2 kWh of heat is generated for 1 kWh of electricity.

Typical SCOP Values:

2.2 Climate Data and Location Determination

The calculator uses two data sources for calculations:

1. EN 14825 Climate Zones (for SCOP calculation):

EN 14825 defines three climate zones for Europe with different weighting factors for SCOP calculation:

2. PVGIS TMY Data (for load profiles and detailed calculations):

For detailed analysis, the calculator loads real weather data from PVGIS (Photovoltaic Geographical Information System) for your location:

• TMY (Typical Meteorological Year): 8,760 hourly values (one full year)
• Hourly temperatures: Real measurement data from a typical year
• Used for: Load profiles, cooling hour calculations, monthly detailed results

The calculator automatically determines the climate zone and loads TMY data based on your location.

2.3 COP vs. SCOP

COP Designations:

• A7/W35: Outdoor air 7°C, supply air 35°C
• A2/W35: Outdoor air 2°C, supply air 35°C
• A-7/W35: Outdoor air -7°C, supply air 35°C

2.4 SEER - Seasonal Cooling Efficiency

SEER (Seasonal Energy Efficiency Ratio) is the equivalent of SCOP for cooling operation.

Typical SEER Values:

2.5 Bivalent Operation

In bivalent operation, two heat generators work together. The air-to-air heat pump is combined with an existing heating system.

Bivalent Modes:

Bivalence Point: The bivalence point is the outdoor temperature at which the existing heating kicks in. Typical values:

• -2°C to +2°C: Standard for well-insulated buildings
• +5°C: For older, poorly insulated buildings
• -5°C to -10°C: For very efficient air-to-air systems

2.6 Annual Heating Demand

The calculator determines annual heating demand using a simplified method based on the climate zone:

Qh = Heat load [kW] × Heating hours_climate_zone × 0.4

Parameters:

• Qh: Annual heating demand [kWh/a]
• Heat load: Design heat load [kW]
• Heating hours_climate_zone: From EN 14825 (4,910 h for Average, 3,590 h for Warmer, 6,446 h for Colder)
• Factor 0.4: Accounts for the fact that full heat load is not required for all hours (part-load operation)

Example for "Average" Climate Zone (Germany):

Heat load = 5 kW
Heating hours = 4,910 h
Qh = 5 × 4,910 × 0.4 = 9,820 kWh/year

Step-by-Step Instructions

The calculator guides you through a 6-step wizard. Here we explain each step in detail.

3.1 Step 1: Choose System Type

In the first step, choose between Single-Split and Multi-Split.

Decision Guide:

3.2 Step 2: Enter Location

The location determines the climate data for the calculation.

Input Fields:

• Country: Germany, Austria, Switzerland, France, Italy
• Postal Code: ZIP code
• City: Automatically completed or manually entered

Automatically Determined Values:

• Design Outdoor Temperature: Lowest expected temperature (e.g., -10°C for Berlin)
• Climate Zone: Average, Warmer or Colder according to EN 14825

You can manually override the design outdoor temperature if you want to use different values.

3.3 Step 3: Select Equipment

In this step, you select specific devices from our catalog.

Selecting Outdoor Unit

Filter Options:

• Manufacturer: Daikin, Mitsubishi, LG, Samsung, etc.
• Heating Capacity: Range in kW (e.g., 2.5-5.0 kW)
• Cooling Capacity: Range in kW

Important Device Data:

• Rated Heating Capacity: Capacity at standard conditions (A7/W20)
• SCOP: Seasonal efficiency per manufacturer
• SEER: Seasonal cooling efficiency
• Max. Indoor Units: For Multi-Split systems
• Min. Operating Temperature: Down to which outdoor temperature the unit operates

Selecting Indoor Units

Indoor Unit Types:

For Multi-Split: Add indoor units one by one. Pay attention to the capacity ratio:

Capacity Ratio = Sum of Indoor Unit Capacity / Outdoor Unit Capacity

3.4 Step 4: Enter Rooms / Heat Load

Here you enter the rooms to be heated with their heat load.

Single-Split: One Room

Input Fields:

• Room Name: e.g., "Living Room"
• Floor: Basement, Ground Floor, Upper Floor, Attic
• Floor Area: in m²
• Heat Load: in kW (or use estimation)
• Target Temperature: Desired room temperature (default: 20°C)

Heat Load Estimation: If you don't know the heat load, you can use the estimation function:

• Well insulated (from 2010): 40-50 W/m²
• Medium insulated (1990-2010): 50-70 W/m²
• Poorly insulated (before 1990): 70-100 W/m²

The calculator uses 60 W/m² as the default average.

Multi-Split: Multiple Rooms

For Multi-Split, you enter multiple rooms in a table:

Import from Heat Load Project: If you have already performed a heat load calculation, you can import the rooms:

1. Click "Import Rooms"
2. Enter the project key
3. Select the rooms to import

Sizing Indicators

The calculator shows color-coded sizing hints:

3.5 Step 5: Bivalence & Economics

This step configures the operating mode and economic parameters.

Choose Bivalence Mode

1. Monovalent (Air-to-Air Only)

• Air-to-air HP is sole heat generator
• Suitable for well-insulated buildings and mild winters
• No existing heating required

2. Bivalent Alternative

• Air-to-air switches off below bivalence point
• Existing heating takes over completely
• Simplest control

3. Bivalent Parallel

• Both systems operate simultaneously below bivalence point
• For high heat demand at low temperatures
• More complex control

4. Bivalent Part-Parallel

• Air-to-air provides base load (e.g., 70%)
• Existing heating covers peaks
• Optimal utilization of both systems

5. Cooling/Transition Only

• Air-to-air only for cooling or transition period
• Existing heating is main heat source

Configure Existing Heating

For bivalence modes 2-5, define your existing heating:

Typical Values by Heating Type:

Set Bivalence Point

The bivalence point is the outdoor temperature at which the existing heating kicks in.

• Slider: -20°C to +10°C
• Typical range: -2°C to +5°C

Rules of Thumb:

• Well-insulated house: -5°C to 0°C
• Medium-insulated house: 0°C to +3°C
• Poorly insulated house: +3°C to +5°C

Activate Cooling (Optional)

If you want to use the cooling function:

Temperature Control:

• Absolute Temperature: Fixed target temperature (e.g., 24°C)
• Relative to Outdoor: Maximum reduction below outdoor temperature (e.g., max. 6K difference)

Cooling Threshold: Outdoor temperature at which cooling starts (e.g., 24°C)

Economic Parameters

3.6 Step 6: Start Calculation

After completing all inputs, click "Calculate". The calculator performs the following calculations:

1. SCOP calculation according to EN 14825
2. Annual heating demand
3. Electricity consumption and operating costs
4. Bivalence split (if active)
5. Economic analysis
6. CO2 balance

The results are presented in 7 tabs.

Understanding Results

4.1 Tab 1: Overview

The overview shows the most important metrics at a glance.

Key Metrics:

Bivalence Summary (for bivalent operation):

• Bar chart: Heat split air-to-air vs. existing
• Annual energy costs breakdown
• Savings compared to existing-only operation

Monovalent Comparison (without bivalence):

• Cost comparison to gas reference
• CO2 savings

4.2 Tab 2: Comparison (Bivalence Only)

Detailed comparison of the two heating systems:

Key Insights:

• How much does the air-to-air HP cover?
• How high are the savings?
• How much CO2 is saved?

4.3 Tab 3: Annual Profile

Monthly breakdown of results.

Monthly Data:

• Heating demand in kWh
• Air-to-air vs. existing share
• Average outdoor temperature
• COP values (average, min, max)

Charts:

• Stacked Bar Chart: Heat split per month
• Line Chart: COP progression over the year

4.4 Tab 4: Efficiency

Detailed efficiency analysis.

SPF Values (Seasonal Performance Factor):

• SPF Heating: Real efficiency over heating season
• SPF Cooling: Real efficiency in cooling mode (if active)
• SPF Total: Weighted average

Efficiency Rating: Classification according to EU Energy Label (A+++ to G)

COP Curve: Chart of COP at various outdoor temperatures:

• At -10°C: COP approx. 2.5
• At 0°C: COP approx. 3.5
• At +10°C: COP approx. 5.0
• At +20°C: COP approx. 6.0

Monthly SPF: Table with COP values for each month incl. min/max.

4.5 Tab 5: Economics

Financial analysis of the investment.

Investment Costs:

Operating Costs:

• Annual electricity costs
• Annual maintenance costs
• Fuel costs (for bivalence)

Metrics:

Cash Flow Table: Year-by-year presentation with:

• Investment
• Operating costs
• Savings
• Cumulative cash flow
• ROI in percent

4.6 Tab 6: Environment

CO2 balance and environmental impact.

CO2 Emissions:

• Annual emissions (kg/year)
• Savings compared to reference (kg/year)
• Percentage savings
• Savings over lifetime (tonnes)

Electricity Mix Scenarios: Comparison of different power sources:

1. Current Mix: National average (380 g/kWh)
2. Green Mix: 100% green electricity (50 g/kWh)
3. Coal Mix: Reference (900 g/kWh)

Primary Energy:

• Consumption in kWh/year
• Savings compared to reference

Illustrative Equivalents:

• Trees planted
• Car kilometers avoided
• Flight kilometers avoided

4.7 Tab 7: Rooms (Multi-Split Only)

Room-by-room result overview.

Table per Room:

Status Indicators:

• Green (OK): Unit matches heat load
• Yellow (Warning): Marginally sized
• Red (Error): Significantly undersized

Economics and Environmental Impact

5.1 Understanding Payback Calculation

The payback period indicates how many years it takes for the investment to be recovered through savings.

Calculation:

Payback Period = Investment Costs / Annual Savings

Example Calculation:

• Investment: 5,000 EUR
• Savings: 300 EUR/year
• Payback: 5,000 / 300 = 16.7 years

5.2 Economic Factors

Positive Factors:

• High gas prices (currently > 0.10 EUR/kWh)
• Low electricity price (e.g., with PV self-consumption)
• High bivalence share (many operating hours air-to-air)
• High SCOP of the unit
• Cooling as additional benefit

Negative Factors:

• Low gas prices
• High electricity price (> 0.35 EUR/kWh)
• Short usage time (only few rooms)
• Very cold winters (low bivalence share)

5.3 CO2 Savings Potential

The CO2 balance depends on the electricity mix:

Comparison with Gas:

• Gas: approx. 200 g CO2 per kWh heat
• Air-to-air with SCOP 4.0 and current mix: 380 / 4.0 = 95 g CO2 per kWh heat
• Savings: over 50%

With green electricity:

• 50 / 4.0 = 12.5 g CO2 per kWh heat
• Savings: over 93%

Tips and Best Practices

6.1 Sizing

Don't oversize:

• An oversized unit cycles frequently (on/off)
• Reduces lifespan and efficiency
• Better: Size appropriately or slightly smaller with bivalence

Rule of Thumb for Heating Capacity:

• Well insulated: 30-50 W/m²
• Medium insulated: 50-70 W/m²
• Poorly insulated: 70-100 W/m²

For 30 m² living room, medium insulated: 30 m² × 60 W/m² = 1,800 W = 1.8 kW heat load

6.2 Optimizing Bivalence

Bivalence Point Selection:

• Too high (+5°C): Air-to-air runs rarely, little savings
• Too low (-10°C): Air-to-air runs even at poor COP
• Optimal: Switch at COP 2.5-3.0 (approx. -2°C to +2°C)

Activate PV Priority: If you have a PV system, activate PV priority. The air-to-air HP will then preferentially use solar power.

6.3 Noise Protection

Outdoor Unit Position:

• At least 3 m from neighbor's bedroom
• Not under your own bedroom window
• Consider sound reflections from walls

Daytime Operation Option: For critical locations, you can disable night operation (only 6am-10pm).

Typical Sound Levels:

6.4 Maintenance

Annual Maintenance Recommended:

• Clean filters (every 2-4 weeks yourself)
• Check condensate drain
• Check refrigerant pressure (professional)
• Clear outdoor unit of leaves/snow

Costs: approx. 100-150 EUR/year for professional maintenance

6.5 PV Integration

Ideal Combination:

• In summer: Cooling with PV surplus
• In winter: Heating with daytime power
• Self-consumption rate increases significantly

Load Profile Export: The calculator can export an hourly load profile. You can use this in the Solar Calculator for PV system design.

Frequently Asked Questions (FAQ)

Can a split air conditioner fully heat my house?

Yes, under certain conditions:

• Well-insulated house (new construction, renovated)
• Open room layout (heat distribution)
• Mild winter region
• Multi-split for multiple rooms

Limitations:

• No hot water preparation
• COP drops at very low temperatures
• Each room needs an indoor unit

What's the difference between SCOP and COP?

SCOP is more meaningful as it accounts for varying outdoor temperatures over the heating season.

How do I choose the right bivalence point?

Rules of Thumb:

1. Switch at COP = 2.5: When COP falls below 2.5, existing heating is often cheaper
2. Economic comparison: At electricity price 0.32 EUR and gas 0.10 EUR → Gas cheaper from COP < 3.2
3. Comfort aspect: Gas/oil works more reliably in frost

Formula for Economic Bivalence Point:

COP_threshold = Electricity Price / Gas Price
COP_threshold = 0.32 / 0.10 = 3.2

At the outdoor temperature where COP = 3.2, switching should occur (typically approx. +2°C).

Is Multi-Split better than multiple Single-Splits?

Recommendation:

• 1-2 rooms: Single-Split
• 3+ rooms, aesthetic requirements: Multi-Split
• Critical application: Multiple Single-Splits for redundancy

How loud is a split air conditioner?

Typical Values:

For Comparison:

• Whispering: 30 dB(A)
• Refrigerator: 35-40 dB(A)
• Normal conversation: 60 dB(A)

Can I completely replace my gas heating?

Complete replacement is possible with:

• Building with low heating demand (< 50 kWh/m²a)
• Multi-split for all rooms
• Hot water via separate instantaneous heater or heat pump boiler

Bivalent operation is more sensible with:

• Old building with high heating demand
• Only partial climate control planned
• Hot water via existing heating

Background Information

8.1 How an Air-to-Air Heat Pump Works

Heating Principle (Simplified):

1. Outdoor unit extracts heat from outdoor air (even in frost!)
2. Refrigerant evaporates and absorbs heat
3. Compressor compresses the gas (temperature rises)
4. Indoor unit releases heat to room air
5. Refrigerant condenses and the cycle starts again

Cooling Principle: The process is reversed: The indoor unit extracts heat from the room, the outdoor unit releases it.

8.2 Typical COP Values at Different Temperatures

8.3 Indoor Unit Types in Detail

Wall Unit (Most Common):

• Installation: On wall, typically 2.2 m height
• Airflow: Downward and sideways
• Advantages: Simple installation, affordable
• Disadvantages: Visible, possible drafts

Floor Console:

• Installation: On floor, under window
• Airflow: Upward
• Advantages: Heat rises naturally, ideal under window
• Disadvantages: Requires floor space

Cassette Unit:

• Installation: In suspended ceiling
• Airflow: 360° downward
• Advantages: Unobtrusive, even distribution
• Disadvantages: Ceiling height required, more expensive

Ducted Unit:

• Installation: In suspended ceiling or attic
• Airflow: Via ducts to outlets
• Advantages: Completely invisible
• Disadvantages: Complex installation, pressure losses

8.4 Refrigerants and Environment

Current Refrigerants:

GWP (Global Warming Potential): GWP indicates how much a refrigerant contributes to the greenhouse effect (CO2 = 1).

8.5 Standards and Regulations

• EN 14825:2022: SCOP/SEER calculation for air conditioners
• EN 14511:2022: Performance measurement at rated conditions
• VDI 4650: Seasonal performance factor for heat pumps
• TA Lärm: Noise protection requirements for outdoor units
• F-Gas Regulation (EU) 517/2014: Refrigerant regulations

9. Further Links

• Air-to-Air Heat Pump Calculator
• Heat Load Calculator
• Solar Calculator
• BWP Climate Map

Last updated: January 2026