Our heat pump system will soon commence its third heating season. The amount of measurement data collected so far has exceeded the capabilities of the software I had once developed; so I crafted a new application based on a real database server. Now you know why I was not very active on social media recently.
I have an excuse to talk about our system again: A reader asked for an English version of one of our German articles.
While I was taming Big Data, the Chief Engineer was fighting with plastic worms and snakes:
The solar/air collector had to be re-built!
In German we say that the shoemaker has the worst shoes – but we did not want our collector to look less cool than the one built with a client recently:
After all, our own system is also the live demo we show off to potential clients!
So here is the new version of our own collector:
One of the guiding principles in designing this system was to use off-the-shelf components only so that it could be built by a DIY enthusiast. Fortunately this type of cheap collector has also superior properties with respect to convective heat transfer.
The heat pump involved is actually the simplest, the ‘most stupid’ device you can buy. We don’t like the trend of equipping any heating system with a so-called energy management system that tries to control nearly any device in the ‘smart home’ – doing all that running on some proprietary black-box software.
We use a freely programmable controller instead – here is a photo from the ‘engine room’:
A controller is needed to control the valves for diverting the flows of brine and heating water, to switch on and off the heat pump and all other supporting pumps, and to log those tons of big data generated by sensors for temperature, flow, and radiation.
A single brine circuit connects the heat pump, the solar/air collector, and the underground water tank. Depending on ambient temperature, water tank temperature and heating demand, the collector may be bypassed.
Here is the latest attempt to draw the hydraulic design in the simplest possible way:
The brine-water heat pump is the same that would be used with ground loops. Every heat pump needs a big reservoir of heat energy, and electrical energy is needed to extract (‘pump’) that heat. Typical heat sources are the ambient air, ground, or ground water.
Different types of heat pumps are used in different countries – I guess for historical reasons and thanks to lobbying of vendors. It seems to me that geothermal heat pumps are more common in Europe while elsewhere air heat pumps are more popular.
With geothermal systems the heat source is a volume of soil – the cylinder surrounding the bore hole or the cuboid confined by the surface above the ground loops.
‘Geothermal’ is a misnomer as this is not real geothermal energy from the core of the earth that’s harvested here – it is energy from solar radiation stored within with first 100 m of ground within the warm season. This is true both for ground loops placed in about 1,5 m below the surface, as well as for deep bore holes.
But the principle is the same if you immerse those loops in water – you could put them into a pond!
We had been searching for an option to heat our old house, and that can be built rather easily – that is: without creating a huge pile of soil we had no place for ‘parking’ it while installing ground loops. In the region where we live, traditional homes and premises are rather small – the plot layout resembling stripe-like elongated rectangles. Think 5×15 m2 house on 10×60 m2 land.
These old houses had been very small farm houses decades ago – we found some remainders of the equipment for processing grapes in the shed. In contrast to other regions, splitting of farm land among heirs had not been forbidden for a long time – so individual property became smaller and smaller. These pieces of land are called ‘belt fields’ because of their shapes.
Here is a video documentation with English subtitles – about the traditional Pannonian ‘Streckhof’ (‘stretched house’).
Cellars were small as well – only about as 1,75 m high with an area of just a few square meters:
This cellar was converted to a water tank:
The cellar has been made water-tight with pond liner. The heat exchanger is immersed in the water – the ‘loops’ have been built from the same type of ribbed plastic pipes as the solar collector in the garden.
The performance of a heat pump is the better the higher the temperature of the heat source is. But even when the water starts to freeze the temperature remains at 0°C degrees and thus the performance of the heat pump is kept at reasonable levels. The energy gain from freezing is high: One cubic meter of water translates to 93 kWh.
From previous discussions on this blog I learned that it might be helpful to add some ‘cultural’ or ‘political’ context:
A heat pump system does of course not make you less dependent on electrical energy – but it makes us here in middle Europe less dependent on Russian gas while providing the same convenience to the user. We have fairly good power infrastructure and upgrades to the (smart) grid are required as we need to integrate decentralized sources renewable energy like solar power and wind power.
Heat pumps can help to make grid operations easier as they usually heat a hot water buffer tank (or the concrete ‘buffer’ of the house). So utilities may cut off electrical power for some hours at an arbitrary point of time as heat pump systems need to have energy storage for ‘offline times’ built in.