When you are an electrical engineer, you can calculate energy savings in your house

The topic of sustainability got us interested more than fifteen years ago

He got to the topic of passive houses by chance. When he was right after graduating from school and about to do his military service, he came across a book called Low-Energy Houses. “Back then, it was something different from today, of course, when the energy efficiency requirements have become a standard. It fascinated me immediately, but I had to wait a few years before I could bring it to life.

When we got a property with the possibility of building a house from my grandma, I finally had a chance. My wife remembered a classmate from comprehensive school who had become an architect. She was the perfect match for us because she was a visionary who had already dealt with the problem of carbon footprints of materials in 2007. Thanks to her experience, she was able to start designing a passive house study for us,” Martin Tesař reminisces about the time fifteen years ago, when the question of sustainability was yet to become a critical part of social discourse.

It was the architect who firmly stuck to details, even though the project outcome was not a passive house but just a low-energy standard. “If I had to say what I would have done differently, it would certainly not have been the thermal insulation solution or the strategic concept of the house. Maybe it would have been some of the dispositions, but the overall result is that we do not spend too much on heating.

If there were a great crisis, we would be able to heat the house up with one wood stove, which we keep separately.” adds Martin Tesař.

If everyone lived like this, people would not make such a fuss about energy bills

The house is open but it is heavily insulated. It is surrounded by a 25cm layer of expanded polystyrene. “Speaking from experience, I know that if everyone in central Europe had a chance to live like this, there would be much fewer people dealing with the bill prices.

If I stop heating in the evening and the outside temperature is around zero, the temperature inside lowers just by one degree till the morning.

Paradoxically, our friend, the architect, pressed us to get better heating, but I just brushed it aside back then because we did not have money for it, and we installed a conventional electric boiler which was just fine. It has been easy to heat up the building for the last twelve years anyway, and the bills have been very reasonable.”

Investing in the heat pump was cheaper than expected

“She was trying to make me buy a wooden pellet boiler or a heat pump back then. I refused it, but two years ago, I finally bought a heat pump. I got rid of the electric boiler, which was not very expensive, and I can say that the heat pump was quite a pleasant surprise.

The investment was not as high as I had originally thought. I discussed it with a friend of mine as well, who told me heat pumps were not as expensive as they said (it was in 2021). I bought a pump of a Swedish-Czech brand and have been satisfied so far.”

I am currently working on a photovoltaic off-grid system

“I also want to have photovoltaic and I am currently working on it; however, it is a self-help job. I have chosen a solution that allows me to be independent of a distributor and avoid too much paperwork, and the off-grid system enables this. ‘Off-grid’ means that something is connected to the distribution grid only as a household appliance, does not supply anything into the grid, and it tries to use maximum energy directly in the house,” explains Martin Tesař.

It is not just about the payback but also safety

When asked whether the investment into the low-energy house components has returned yet, Martin Tesař answers evasively. “I am sure the payback can be calculated somehow, but you always have to calculate the savings in comparison with something else, and I ask, in comparison with what? With a typical Czech house from the 60s or the average house from 2007?

Anyway, speaking of our house, with a low-energy standard, it is said that one pays approximately up to 10 percent more than when building a standard house. And I can confirm that.

I bought a bit more expensive triple glazing windows; they cost a little more money but not by high multiples. Regarding the insulation, it was tens of thousands of CZK more. The structural work was a self-help job that I completed together with my family. My approach was a bit strategic and precautionary from the start. I can be sure and confident we can survive even in the case of a blackout.”

I measure economic sustainability

If he was to build the house again, he would use less concrete. “It is a great material in terms of construction; however, it is not very sustainable.

It certainly depends on the location, but I would not be afraid of a wooden house nowadays.

Economic sustainability is something I have counted and I am currently measuring. I can say that for heating – now it seems so, even if I estimate the development until the end of the heating season, plus there are five of us in the house – we spend 0.4 megawatt hour for a person. When I extrapolate it, let’s say, to 10 million Czechs and look into the statistics to see how much is spent on heating in houses in our country (57 TWh in 2020, source Czech Statistical Office (CSO): Household Fuel and Energy Consumption Energo - 2021.

I would say we are in the fantastic one fourteenth of an average Czech’s consumption. Even if we add the efficiency of gaining electricity from the primary sources, we still have a nice and fair one fifth.

Of course, it also results in interesting financial savings. When one kilowatt hour costs 2 CZK, the savings gained thanks to using a heat pump do not play an important role in a low-energy standard. But when one kilowatt hour costs the current capped 6 CZK or even 10 CZK from the price lists (January 2023), the payback period of my heat pump is about 8 (or rather 5) years.” He really cannot deny he is an engineer.

Building a house is an excellent course for managerial skills

How did the building work enrich Martin Tesař’s professional life? Based on his answer, it helped in many ways. “While building, one gains some soft skills and managerial skills. They can focus on the important things and not lose time with small details.

On the other hand, it is reflected in the electronics development because our company – and this is not our unique way, but the experience has strengthened the approach in me – we aim at offering solutions with the lowest possible consumption. Let’s say, within the physical limits, and if the consumption is higher than expected, there must be a reason.

For example, the reason can be it is a top-quality, unique device that is not manufactured in thousands but only in a small number of pieces where the performance plays a more significant role than the consumption.”

Do not skimp on insulation

And what is some practical advice for everyone? Rule number one is not to skimp on insulation. People should consider the fact that the insulation material is rarely the most expensive part of the construction. Secondly, choose a good project architect.

Every electrical engineer can roughly calculate the energetic demand of a house, and if they know Ohm’s law and how to add up electrical resistance, then it is not rocket science.

As it is very similar in the thermal area – the physical quantities and rules are pretty much the same – you just need to exchange electrical resistance for thermal resistance.

In practice, you simply need to calculate the surface of the building enclosure and the windows, know the thickness of the insulations, and find out the heating parameters of the windows (from a catalog or the supplier’s offer).

When you have all the information, it is just about multiplication and adding up on a few lines in Excel or on paper. It is that easy.