11 Questions To Ask

1. Should I really buy a heat pump or do I have more possibilities?

Of course you have. A gas boiler (provided you have gas fixture available), electric boiler, fireplace insert, firewood or coal-fired or corn boiler, etc. Another possibility is solar system. Each of these alternatives offers its advantages and disadvantages. Purchase costs of firewood or coal-fired boilers or fireplace inserts are lower, but you have to take all the associated work into account - firewood preparing and stoking, no matter how tired you are, coming home after all-day hard work. The other systems offer much more comfortable operation. The heat pump, however, offers lower electricity fee for almost the whole day (22 hours), not only for heating but for other devices, too. In their essence, the heat pumps consume less electricity compared to electric boiler (by up to 2/3), thus saving costs and your wallet. Compared to energy price increasing at the input, the price of heat from the heat pump increases only by 1/3, because the heat pump works with heat factor 3 on average.

2. Can I use the heat pump with my heating system?

To operate optimally, the heat pumps need to work with temperature in the heating system up to 55°C. Connecting the heat pump with floor heating is very effective. As for radiator heating, experts (heating designers) recommend that thermal gradient is set to 50/40°C. For the floor heating, the heating water thermal gradient is often lower, down to 30/25°C. You have the heating system (e.g. radiators and electric or gas boiler) and you want to make sure whether you will have thermal comfort at your home after installing the heat pump and what the expenses for energies will be?

We recommend that you perform the following test:

  • set the heat source to 50°c, 55°c for the test purposes
  • set the space regulator to the diurnal temperature to e.g. 23°c
  • set the space regulator to the night temperature one degree lower - 22°c

Note: Bigger attenuation is not prerequisite for the source of heat which covers the thermal loss and does not have significant thermal margin of power. That would result in higher energy consumption for heating while having lower thermal comfort, especially in the morning.

3. What type of heat pump should I choose?

The heat pumps are produced in many types. The first word stands for medium where the heat is taken from - air, ground or water. The second word stands for medium which the heat is delivered to. Currently, there are mainly the following types of heat pumps:

  • air/water
  • ground/water
  • water/water
  • air-air, etc.

Click here for advantages and disadvantages of each single type.

4. What power should my heat pump have? How do I calculate it?

The heat pumps are designed based on so-called thermal losses. The thermal losses (heat demand) of a building change with the outside temperature. The heating system designers use tables to calculate the thermal loss for a specific area (e.g. Brno has calculating area -12°C, while Žďár has -15°C). One completely same family house can have different thermal loss in a different area, meaning you would need heat pump with different power. However, the calculated thermal losses - estimated energy consumption - depend also on investor demands for the interior temperature in the building. You must realize that each one extra degree represents 6% of the source power. We recommend that you tell the designer what temperatures you demand in individual rooms as table calculation temperatures for habitable rooms are only 20°C.

In the heat pump power, it is advisable to take into consideration whether it will heat up the domestic hot water and/or heat the outdoor or interior pool. Heat pumps should be rated by experienced experts (e.g. heating designers).

Basic consideration:

  • radiator heating system - for thermal gradient of 55/40°c
    thermal loss of a house, to ensure the thermal comfort of 22°c, is e.g. 14kw at outside temperature of -12°c.
    what’s important to know is that at outside temperature of +5°c the thermal losses are at 40-45% of the calculated maximum value at -12°c (6,3kw), at 0°c=tl 55%, -5°c=tl 80% and at -12°c, tl=100% (14 kw).
    recommended heating power of a heat pump for thermal losses of 14kw at -12°c for radiator system would as follows: (14kw*0.80=11.0kw at a-5/w50).
  • floor heating system - for thermal gradient of 35/30°c
    thermal loss of a house, to ensure the thermal comfort of 22°c, is e.g. 14kw at outside temperature of -12°c.
    what’s important to know is that at outside temperature of +5°c the thermal losses are at 40-45% of the calculated maximum value at -12°c (6,3kw), at 0°c=tl 55%, -5°c=tl 80% and at -12°c, tl=100% (14 kw).
    recommended heating power of a heat pump for thermal losses of 14kw at -12°c for radiator system would as follows: (14kw*0.80=11.2 kw at a-5/w35).

Such projected power of a heat pump is the most appropriate for heating from the economical point of view. But there is a hitch in it - you need to have heat pump with controlled power, i.e. heat pump equipped with a frequency converter to control the heating output in the range of 40 to 120%. Provided the heat pump is not equipped with the output regulation, it is necessary to progress cautiously when deciding the heat pump power. It is not always true that the higher heat pump power, the more I save.

5. Is it always necessary to install second (bivalent) source together with a heat pump? Is a gas boiler convenient auxiliary source?

A bivalent (auxiliary) source does not always have to be installed. A family house needs heat already at 15°C. Heat consumption input-output curve of a house is not linear. For example, let’s suppose your house’s thermal loss is calculated to 15kW (at -12°C), then at 0°C you need to distribute 60% (9kW) from the energy originally calculated at -12°C to your house. The same house consumes as much as 80% of the calculated thermal loss at -5°C outside temperature. From the average winter temperatures data we can tell that 100% of the heat pump’s power will not be used relatively often. In addition, most of the heat pumps do not control output (using a frequency converter), so the electrical parts are often switched off/on, thus reducing the lifetime of the whole heat pump. Heat pumps with higher power are also more expensive while not necessarily optimal solution. We recommend that you consider the cost/performance ratio. With MACH heat pumps, any switchable source, i.e. gas boiler or mostly electrical boiler (divided into more power levels), can be used as bivalent source.

6. What capacity should the domestic hot water sink have?

This is difficult to advice. This depends on requirements of the house residents. Someone will do with 15 litres of hot water to take a shower and someone cannot make do with 200 litres. From our experience, we can say that a sink of 200 litres is sufficient for a family of four if it’s treated economically. However, if your demands are higher, we recommend that you use 300l sink. Bigger capacity allows heating the domestic hot water to a lower temperature, e.g. 48°C instead of 55°C. With a sink of bigger capacity - 300l instead of 200l - you will achieve lower costs for the domestic hot water heating. This solution also opens opportunity e.g. for maximum utilization of future solar system.

7. What should I take into consideration when comparing various price offers?

You may come across false advertising, mainly giving false heating factors or heating factors with which the heat pump cannot operate in the building. Let’s suppose that company A offers 15kW power for CZK 280,000 (about EUR 11,666) while company B offers for the same family house 10kW for CZK 300,000 (about EUR 12,500). Everything argues for company A. But, taking a closer look at the parameters for both heat pumps, company A offers 15kW with A7/W35 parameters (at temperature of outside sucked air 7°C and heating water temperature 35°C), while company B offers 10kW at A-7/W50.

Company B offers more powerful heat pump compared to company A, thus the higher price is reasonable.

For customers, operating heating factor is much more important - the heating factor at which the heat pump will operate on average for the whole heating season (or a year). Solid vendors use the operating heating factor to calculate return on investment. For ground/water and water/water heat pumps, also consumptions of circulation pumps at primary site (relates to plane collector/underground collector or submersible pump in the well) are used for the calculation. Taking the relating power and our climatic conditions, the operating heating factor is better with air/water heat pumps compared to the other types.

Here are our recommendations:

a) Follow the parameters of the heat pumps offered for your heating system very carefully. There is no reason to take the power of 15kW at 35°C heating water into consideration when you will heat by means of radiators with the heating water at 50-55°C. In this case, the heat pump power is lower.

b) For operation economy you need to know the operating heating factor. According to regulation, the heating factor is related to the cooling circuit only. In practise you may end with heat pump with heating factor 4.5 and operation heating factor 2.2. Such a low operation heating factor may be caused by:

  • a low power of the heat pump
  • the bivalent source working too early (already at +5°C)
  • the fact that you need to heat the heating water up to a higher temperature than expected

8. Where it is advisable to place the outside evaporator? Are there any limitations?

The evaporators of the air heat pumps should by placed by the walls, not on an open space, where they are exposed to excessive winds or can be covered by snow. In consideration of large amount of water, arising from lamellas (condensate) defrosting we do not recommend to place the evaporators on balconies, roofs and in the vicinity of roads and pathways. More suitable place for the evaporators is to the southern sides and close to the indoor part of the heat pump.

Also, you have to observe the noise level with respect to the neighbouring estate - house.

So, try to find a proper place and ask your vendor for noise level protocol (outdoor evaporator noise level protocol). In case of indoor heat pumps (e.g. MACH IN) you don’t have to take noise into consideration.

9. Which thermal comfort should I heat my house to?

You, investors, want the temperature in the habitable rooms to be 22 or 23°C. However, the hitch is in the fact that thermal losses are usually calculated using the standard. The standard suggests that the thermal comfort in the habitable rooms is to be 20°C. Provided you demand one degree of thermal comfort above the calculated one, add extra 6% of energies. In practise, this means that a house with thermal loss calculated using the regulation to e.g. 10kW has the thermal loss up to 12kW in fact. And all you have to do is to heat your house to thermal comfort of 23°C instead of 20°C as the standard supposes.

We recommend that you agree on a definition of thermal comfort in individual rooms with your designer before you start to calculate the thermal loss.

10. Which heat pump provides the best savings on operation costs?

Not taking the type of heat pump into consideration, decidedly it is a heat pump with controlled output. What does it mean in practise? The heat pump is equipped with the frequency converter controlling the cooling compressor speed and thus the heat pump’s heating output itself. Such type of heat pump works exactly according to the desired thermal load consumption of your house.

Examples of such heat pumps are MACH IN or Chameleon.

11. How to regulate heating in the house while keeping the thermal comfort and minimum heating costs?

Heating the house can be compared to your car performance on highway (provided it is traffic-free). The smoother driving, the more you save the car itself as well as fuel. If you operate the heat pump to heat your house and set the regulation to night attenuation with temperature of 5°C lower in the house or even switch off the heat source for the night, then you wake up in cold house and the thermal comfort is not reached till the afternoon. The heat pump is in constant operation, increasing the operation costs up to 30%. However, this contention may not be valid in the case of low-energy houses (TL 3 to 5 kW).

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