Air-Water Heat Pump 8 kW for Heating and Cooling a House 100 m²

Heating, cooling and hot water for the needs of a 100 m² house – with just one installation. An air-water heat pump provides the solution to this task. Maximum efficiency with minimum bills.

Task: Find an option for heating, cooling and hot water for a house 100 m² with one installation, as efficiently as possible with the lowest possible bills?

Calculations: Registered heat losses of the house 5.2kWh, at -16°С;

Solution: Air-Water Heat Pump DAIKIN/Redsun 8kW;

COP: 4.4;

El. power: 2.6kW – maximum;

Heating power: 8 kW – nominal;

Annual energy consumption: 4500 kWh;

Average bill for heating and hot water: BGN 119.00/month;

Average bill for cooling and hot water: BGN 27.00/month.

Термопомпа Въздух-Вода за отопление на къща 100 м2

Task for heating, cooling and hot water for a house 100 m²

The condition of the task was to offer the best possible solution for the home’s heating, cooling and hot water needs. The residents of the house are two adults plus one temporary resident youth – so we installed a volume boiler of 120 liters with seprentine.

The construction characteristics of the house are:

  • one-story building with an area of 100m2
  • external walls – masonry with bricks Poroterm 38 N + F – λ (thermal conductivity coefficient)= 0.138W/mK
  • internal walls – masonry with bricks Porotemr 25 N + F – λ = 0.26W/mK
  • joinery – 7-chamber PVC with triple glazing 4C/White/K – Ug (heat transfer coefficient) = 1.1 W/m2K
  • floor – reinforced concrete slab with a thickness of 25 cm – λ = 1.92W/mK
  • ceiling – 20 cm thick reinforced concrete slab – λ = 1.92W/mK
  • floor height – 2.80 m
  • roof – four pitched – wooden structure covered with tiles with λ = 0.99W/mK


  • external walls – Neoprene EPS BASF 25 – 7 cm thick – λ = 0.029W/mK
  • floor – fiber XPS with a thickness of 5 cm – λ = 0.033W/mK
  • ceiling – plasterboard ceiling with stone wool filling 10 cm – λ =0.37W/mK

Calculations of the heat losses of the house to determine the power of the heat pump

The described house with a size of 100 m² is located on the outskirts of the city of Sofia, for this area a calculated heating temperature of -16°C (minus 16°C) is assumed. The temperature desired by the client to maintain in the premises was +23°С. During the construction of the house, we were constantly in communication with the client to discuss the various stages, insulations, capacities, etc. Since he had been “advised” that there would be no need for external insulation when building with these bricks, we did calculations with and without insulation. We calculated that when placing a 7 cm neoprene, it will reduce the heat losses from the external walls by 1.6 kWh at -16°C, which, expressed in money, is about BGN 0.29/hour. The client agreed with us and did the insulation.

We calculated the total heat losses of the house at 4.7 kWh at -16°С, added 0.5 kWh for the water heater and installed a DAIKIN air-water heat pump with a nominal power of 8kW.

Why did we offer a DAIKIN 8 kW air-to-water heat pump when the house’s losses at -16°C are 5.2kWh?

Because as most of us know, the CPR (transformation coefficient) varies with the temperature of the outside air. Theoretically, we calculated that at -16°С temperature of the outside air and 45°С of the water (heat carrier) required for heating with water convectors, the SOR will drop to 2.09 points.

With a maximum heat pump load of 2.6 kW and -16°C outside air, the heat pump would generate about 5.4 kWh of heat energy:

2.6 kW*2.09=5.434 kWh, where:

2.6 kW – consumed current (electric energy);

2.09 – COP – at -16°C;

5,434 kWh – delivered thermal energy per hour in the specific conditions.

Graph of the theoretically calculated COP depending on the temperature values of the outside air (ambient environment)

Графика на COP коефициент на термопомпа въздух-вода DAIKIN 8kW

Prediction of the monthly heating bill with a DAIKIN/Redsun 8kW heat pump

As part of the implementation of the heat pump system for heating, cooling and hot water, we offer forecasting of the monthly heating bill. This involves a lot of calculations and data, as well as taking into account the characteristic features of the home/house/apartment…

*In the month of September, the estimated heating bill is BGN 0.00, because the heating season in Sofia starts in October.

Прогнозна сметка за отопление

The following data is embedded in this projected account:

  • Area of residence (geographical)
  • Heat losses in relation to building characteristics
  • Desired temperature to maintain
  • Sun degrees for the relevant geographic region
  • Duration of heating
  • COP of the installed heat pump for the different months depending on the temperatures
  • Price of electricity
  • Required amount of thermal energy for 1°C
  • and other specific data

A simplified formula for predicting the monthly heating bill:

HDDtQ*€/COP=lv/month, where:

HDD – heating degrees for the relevant geographical region for the relevant month;

t – daily duration of heating – hours;

Q – necessary amount of energy for the increase of one degree in the specific calculated dwelling/home;

– price of electricity;

COP – coefficient of transformation of the heat pump for the corresponding month.

If we take for example the month of November:

HDD = 537 [Average temperature for the month = 5.1°C, desired maintenance temperature = 23°C, number of days in the month = 30 ⇒(23-5.1)*30=537];

t = 24 hours per day;

Q = 0.130 kWh/1°C – the amount of heat energy needed to raise one degree in the corresponding heated room/home;

= BGN 0.19/kWh – price of electricity;

COP = 3.18 (transformation coefficient of the corresponding heat pump at an average monthly temperature of 5.1 °C and water temperature in the heating installation of 45 °C.

537240.13*0.19/3.18=BGN 100.10/month

Installation of a DAIKIN 8kW air-water heat pump

Stage 1 – Laying of pipe installation

After making the necessary calculations (which are an extremely important part, if not the most important part, of a maximally efficient system) we moved on to discuss the various stages of heat pump system installation and construction.

Since the house was under construction, it was absolutely possible to synchronize the various stages of the heat pump construction with the construction stages of the house. In this way, there is no need for rework, chipping, plastering and many other unpleasant, time-consuming and financial procedures.

Since the house was under construction, it was absolutely possible to synchronize the various stages of the heat pump construction with the construction stages of the house. In this way, there is no need for rework, chipping, plastering and many other unpleasant, time-consuming and financial procedures.

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A test was made for the tightness of the laid pipe installation and we finished with this stage.

Stage 2 – installation of water convectors

Some time after the first stage, it was time to continue building the system. In the construction of the house, the processes of the screed on the fiberboard floor and the pipe lines laid by us, the walls were plastered and many other construction works were completed. We maintained constant contact with the client and synchronized our actions.

At a convenient moment for him and for us, we went, installed and connected the SABIANA water convectors for heating and cooling. We laid the condensate lines (in cooling mode), all the pipes went to the gutters of the house.

We also installed and connected the water heater.

We did a system test again, everything was fine and we are done with this stage.

Stage 3 – installation and commissioning of the DAIKIN 8kW air-water heat pump

With almost all of the house building processes completed or nearing completion, the client was ready to move into their new home. The time has come to install the heart of the entire heating, cooling and hot water installation, the DAIKIN 8kW air-to-water heat pump itself.

Let’s bring the solution of the task to the end.

We installed the external and internal body of the heat pump, made the necessary tests, measurements and samples, put the system into operation and explained the necessary details to the client.

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How much did it cost to build the heat pump heating, cooling and hot water system for this 100 m2 house?

Most likely, we are all interested in this, how much does it cost? Yes, this is a very important factor, but it is also important to note the many other benefits of having a heat pump system for heating, cooling and hot water, such as:

  • independence
  • comfort
  • possibility of remote control
  • heating, cooling and hot water in one
  • non-commitment to the system
  • no dust, no smoke, no cleaning, no charging…
  • peace and rest in an air-conditioned atmosphere
  • maximum efficiency
  • minimum bills
  • and many, many other pluses

And yet let’s face it, the construction of the entire system with all related elements, components, assembly and testing processes cost the client BGN 17,500. Including:

  • Heat pump DAIKIN 8kW – indoor and outdoor unit
  • Boiler 120 liters with coil
  • Pipe lines with pipe insulation
  • Collector box
  • Adjustable manifolds
  • Digital room thermostats
  • Water convectors for heating and cooling
  • and many other small and NOT so small parts and components.

If you are interested in building a heat pump system for heating, cooling and hot water for your home, contact us!

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