Often blog articles have been motivated by frequently asked questions and answers - here we list these questions and concise answers, plus links to related blog postings. FAQ belong in these categories:

Heat Pump System LEO_2 -- Monitoring and Control  -- punktwissen

Last change: Video link added, related to question: How is the underground tank built?

Heat Pump System LEO_2 [Top]

Heat Pump System LEO_2 - hydraulic schematic

  • Can you briefly explain how the system works? A standard brine-water heat pump (as used with geothermal systems) extracts heat from a combined heat source - an underground water tank plus an unglazed solar collector. Energy is gained from cooling and freezing water, and also from the surrounding ground. See this 1-page overview and this blog posting plus answers to first questions in the comments:
    [2013-02-26] Controlling the Four Elements. Or: Why Heat Pumps Are Cool
  • How is the solar collector built? Are there different options of the design and can it be used for other purposes, too? The actual collector is an array of black flexible ribbed plastic pipes. They can be attached to different supporting constructions of different shapes - we recommend e.g. larch wood. It can have added value, when also used as railing, fence or espalier for plants (in summer; only in winter the collector should not be covered by leaves.)
    Images of the collector as railing / fence on top of a garage:
    [2014-05-31] Art from Plastic and Wood
    Free-standing fence on the ground:
    [2014-09-07] Big Data, Big Plastic Worms, and How to Utilize Your Cellar
    Espalier for tomatoes:
    [2013-08-14] Welcome to the Real World! 
  • Why invest in a solar collector if the performance factor decreases just a bit if you turn it off? This was a question in relation to data for the season 2014/2015, including the 'Ice Storage Challenge' when we had turned the solar collector off for the whole February. The performance factor was only slightly lower that month implying only a modest increase in energy costs. But this was only possible because the energy in the tank was filled to the brim as the collector had been used all the months before! So the solar collector is not an option, but an essential component. In our climate the croitical months are Dec-Jan-Feb, when ice is created in the tank. But even then, the solar collector is providing about 75-80% of the ambient energy needed by the heat pump.
    The following post was written to clarify this point, brought up in a discussion on data for spring 2015 (when the solar collector had been turned off).
    [2015-10-14] Economics of the Solar Collector.
    Detailed data analysis of season 2016/17: The contribution of the collector is increasing with decreasing tank temperature. This is symbiosis: The collector can harvest a lot because of the tank, and the tank needs the collector for recovery.
    [2017-02-05] Earth, Air, Water, and Ice.
  • How is the underground tank built? Can it have any shape? The layout of our heat exchangers has originally been optimized for a cuboid ice / water storage. Based on flexible, 'LEGO-style' building blocks (introduced in 2016) the heat exchanger can be fitted to cavities of different shapes, incl. cyclindrical ones (e.g. off-the-shelf rainwater cisterns). An existing root cellar, cesspit or cistern could possibly be re-used. The tank / cistern needs to be damp-proof (using a special type of concrete or pond liner) and has to have some kind of lid / entrance. It has to be insulated against cold air from above and closed tightly so that no small animals get in. If additional insulation material is needed depends on the depth the cistern.
    [2017-07] A client / DIY ice storage system builder has made a video: Two cylindrical cisterns are delivered and buried.
    [2014-12-14] Cistern-Based Heat Pump – Research Done in 1993
    [2014-09-07] Big Data, Big Plastic Worms, and How to Utilize Your Cellar
  • Does the water in the tank smell? Same arguments as when using a rain-water cistern: Normally, it does not, but anaerobic decomposition can result in the production of hydrogen sulfide - we tested this accidentally when brine leaked into the tank, on rebuilding the solar collector. This was food for bacteria:
    [2014-09-28] Biology / Chemistry Challenge or: Should We Really Blame the Dead Frog?
  • Which kind of heat pump do I need? A simple off-the-shelf brine-water heat pump, actually the most stupid (and cheap) one that lacks 'smart' energy management features. Our control unit would use the same electrical contact a utility might use (in Europe) to turn the heat pump on an off.
  • Can you provide performance data for operations of the system under realistic conditions? We provide detailed data gathered since autumn 2012, and consolidated into diagrams and monthly / seasonal numbers. The seasonal performance factor is well above 4, even when including hot water heater and using radiators on the ground floor.
    [2016-10-21] Same Procedure as Every Autumn: New Data for the Heat Pump System.
  • Is this system intended to be the only (monovalent) heating system of a home? Yes - the tank and collector are sized to meet this goal, that is: freezing water will provide enough energy to heat the home even in a period of several cold 'ice days' in a row. This posting gives some numbers - once every 10 years the backup electrical heating element might be switched on; but this would not impact the economic assessment:
    [2015-01-28] More Ice? Exploring Spacetime of Climate and Weather.
  • How does the behavior and performance change when water starts to freeze? How fast will the ice melt again? The Coefficient of Performance drops a bit when the temperature of the ice cube starts to decrease. Here a the results of a long-term experiment in simulating an exceptionally harsh winter - and thus large ice cube - by turning the solar collector off. Melting is much faster than freezing: even in March the solar collector is already providing enough energy to melt the ice and cover the heating demands of the house.
    [2015-04-01] Ice Storage Challenge: High Score!
    [2015-03-08] The Ice Storage Challenge.
    [2015-01-15] We Want Ice!
  • How big does the 'ice storage' tank need to be? What about rare extremely harsh winters? The important numbers are: The energy needed per heating day on a 'really cold day' (dependent on insulation, size of the house, and climate), and the typical number of consecutive Ice Days - as the latter determines how big the storage tank needs to be. Our tank (25m3) might hit its limit about once in 10 years. We estimate that about 90% of the volume could be utilized. The limiting condition is the slowly decreasing brine inlet temperature as the layer of ice that is cooled below 0°C. The heat pump switches to the backup heating element at brine temperatures of -6°C.
    [2017-02-22] Ice Storage Hierarchy of Needs.
  • Do you provide simulations? Yes, we can model the behavior of a 'standard' LEO_2 system (ice/water tank, solar/air collector, hygienic storage tank, buffer tank, brine/water heat pump) based on ambient temperature data for a particularly cold winter. Note that such a detailed simulation is not required for system sizing - here we used a simplified calculation based on our measurements and simulations.
    [2017-05-02] Simulating Peak Ice.
  • Why don't you use a flat plate or vacuum tube collector but an unglazed collector instead? We picked it deliberately - not for the low price, which is a side-effect. This collector mainly harvests energy from the ambient air, via convection. In winter the ambient are is often still much warmer than brine which allows for a very effective heat transfer (in contrast to low energy gains from solar radiation.
    [2014-04-13] Measurement Data for Our Heat Pump System – Finally Translated Documentation - section titled: Can I use flat plate collectors?
  • How much energy does ground contribute? Your results are for wet soil - what change do you expect with rocky underground? In a typical year here (ice peak well below maximum) the contribution of wet, dense soil would be in the same order of magnitude as freezing of water. We get about 1000kWh from ground in the critical months Dec-Feb. Wet soil delivers about 15W per square meter of that part of the interface between ground and the tank below frost depth (comparable to numbers used in sizing ground loops).
    We expect this to be lower for rocks due to lower specific heat, and you cannot harvest energy from freezing ground (as we saw when the ice cube touched the walls of the tank). In addition, it depends on the depth of the tank, and: the larger the tank is, the smaller the surface is in relation. So in sizing systems we do not overestimate the contribution. (Excerpt from this list of answers to various questions in the blog's comments).
    Detailed analysis of the contribution of ground, from data analysis of the season 2014/15 - when we turned off the solar/air collector to simulate a harsher winter.
    [2017-02-05] Earth, Air, Water, and Ice.
  • You are heating hot water indirectly - why and does it really get hot enough? With a heat pump, you aim at keeping the temperature of the water as low as possible (to keep the performance factor high). So the hygienic storage tank needs to have a large internal heat exchanger surface - then a tank temperature of less than 50°C still results in tap water temperatures well above 40°C (We are our own most critical clients in that respect).
    Quick intro and hydraulic schema in this answer to the question How do you heat hot water?
  • How does cooling work? The heating circuit (floor loops) becomes 'floor cooling': The cool water in the underground tank cools brine which in turn cools the water in the buffer tank that is other used for hot heating water in winter. It is not AC-like cooling, but it is simple (no reverting the cycle of the refrigerant) and you heat hot tap water in parallel to cooling will actually help cooling!.
    [2015-08-11] Having Survived the Hottest July Ever (Thanks Natural Cooling!)
    [2014-09-07] Answer to the question Where's the capacity to cool in summer?
  • How warm does the underground tank / cistern become in summer? See the red line in this image for the typical change of temperature. After the cold season the temperature is limited to 8°C to prepare for cooling – the collector is bypassed to keep the temperature constant. When the tank is used for passive cooling and ground is heated up by the sun, the temperature exceeds the set point. In autumn the temperature is limited to 20°C (max. temperature allowed by the heat pump vendor).
  • Can you describe a typical project? We have summarized the essential steps at the page about our services re heat pump systems. This postings shows a client's system in the making:
    [2014-05-31] Art from Plastic and Wood
    We also work with clients whose sites we never visit - so these are remote-only projects. A typical project is chronicled on our German blog in a series of posts 'Im hohen Norden'.
  • Please give me a primer on the underlying physics!
    [2016-01-22] Temperature Waves and Geothermal Energy: Calculation and cross-check of the figures shown in intros on geothermal energy.
    [2015-06-01] An Efficiency Greater Than 1? The Coefficient of Performance of a heat pump is much greater than 1 which is due to the definition, omitting input ‘ambient energy’.
    [2015-04-21] How to Evaluate a Heat Pump’s Performance? On the definition and measurement of performance indicators.
    [2015-04-01] Ice Storage Challenge: High Score!
    [2015-02-14] A Sublime Transition - on the intricacies of the phase transitions between water, vapor, and ice.
    [2015-01-28] More Ice? Exploring Spacetime of Climate and Weather - accounting of the energy in the water tank.
    [2014-10-04] Pumped Heat from the Tunnel.. Cross-check of numbers for a large heat pump system.
    [2012-12-10] The First Heat Pump Ever Was Built in Austria Historical background.
    [2012-05-10] Why Do Heat Pumps Pump Energy so Easily? Brief explanation how a heat pump works.
  • Do you recommend photovoltaic solar panels and/or solarthermal flat plate collectors? Can you cover the heat demand with solar energy? We don't recommend 'classical' solarthermal collector as would make the setup more complex but add little in terms of economics. Photovoltaics makes sense economically (in AT), especially if the hot water heating cycle of the heat pump is more aligned with solar energe production. But unless the building is a small home built according to low energy standards PV cannot cover a substantial part of head load in northern latitudes, as our review of the first year of operating PV generator plus heat pump shows:
    [2016-06-22] First Year of Rooftop Solar Power and Heat Pump: Re-Visiting Economics
    [2016-06-01] Photovoltaic Generator and Heat Pump: Daily Power Generation and Consumption (see also Q&A in the comments)
    In summer it would be possible to be nearly autonomous with a reasonably sized battery:
    [2015-12-07] Half a Year of Solar Power and Smart Metering. In summer, our building's electrial power baseline is higher than the heat pump's demands for heating hot water - so it makes sense to align hot water heating with PV production. When the heating season starts, the heat pump typically needs more energy per day than produced by PV.
    [2015-11-13] The Impact of Ambient Temperature on the Output Power of Solar Panels. Analyzing our monitoring data – combining logging from our heat pump’s control unit (UVR1611) and the PV inverter’s logging.
    [2015-06-17] Solar Power: Some Data for the First Month. Figures and numbers from our PV generator’s logging: Combining daily energy balances with data from our power meter, and tracking intermittent short and very high power spikes by parsing the inverter logger’s website.
    [2015-05-18] Two Weeks After Lift-Off. Mainly on safety features.
    [2015-03-23] We Have Come a Long Way: Rooftop Solar Power Now! Installation of the system.
    Batteries are not yet economical. Even if they are as cheap as Tesla's prices (as per announcments of selling prices in May 2015), the payback period is likely to be about the life time - see a first estimate in this discussion. The backup function is hardly needed here as the downtime is so low and in winter the batteries would be way too small anyway. (Answer to a question on the assessment of a battery)
  • Who is the target audience? Can home owners build this system themselves? LEO_2 goes well with buildings / premises too small for installing proper ground loops and/or is targeted to clients who want to use simple passive cooling in addition to heating. The system is also a cheaper alternative to groundwater or borehole heat sources. In contrast to air heat pumps or small ground loop heat sourcs the seasonal performance factor is higher. Our typical clients are tech-savvy home owners who are e.g. also very interested in monitoring, control, and optimization of their systems. All components are simple off-the-shelf products, and the system can be built by a motivated DIY enthusiast, we provide know-how on how to build the heat exchangers and provide the programming of the control unit
  • How do you measure the volume of ice in the tank? We measure the increase in surface level. (That's feasible as the ice does not float but start growing from the heat exchanger tubes). For a long time we had just read off a ruler. Now we measure via the pressure increasing linearly with depth:
    [2017-04-08] Mr. Bubble Was Confused. A Cliffhanger.

The system had been developed with having Austrian/German/Swiss climate, regulations, energy costs, status of the power grid in mind. The following FAQ have been derived from discussions with people from other regions:

  • Can yor provide some background on the typical heating power / electrical power used by homes in your place? (Allowing for a comparison of culture and politics).
    [2015-02-27] “An Unprecedented Test for Europe’s Electricity System”. Solar power is huge - also due to many decentralized rooftop generators.
    The alternatives to a heat pump system typically considered here are either natural gas (same convenience, no fuel storage) or wood pellets (also renewable, needs storage room, and won't run without electricity either, and generates emissions). We developed this system to get rid of the dependency from Russian gas; and having been able to re-use a root cellar as a heat source we found it more straight-forward than pellets:
    [2014-09-07] Big Data, Big Plastic Worms, and How to Utilize Your Cellar - history of our system plus some cultural context.
    [2015-12-07] Half a Year of Solar Power and Smart Metering. Consumption (and production) of electrical energy, May-November 2015 - monthly and daily energy balances. In one year the heat pump's compressors uses about 50% of the total energy. Our building meets the statistical average in Austria - about 3.500 kWh in a year, excl. heating / cooling.
  • Is this system economical? Given Austrian costs of electricity it is - see an estimate of energy costs of the heat pump system compared to costs of natural gas here. Inserting efficiencies of other heaters and costs of electricity and other fuels would give you an idea about economics in other regions.
    [2015-09-29] Heat Pump System Data: Three Seasons 2012 – 2015.
  • Isn't is a big risk to rely on a heating system powered by electricity in case of a power outage? Basically all heating systems here depend on electrical power to some extent - using circulation pumps for the heating water, or for transport of the fuel, or the control unit. The average outage time per utility client in Austria is less than 1 hour / year:
    [2015-01-22] Personal Risk Assessment. - a posting related to this question about power outages.
  • Would the system work in Canada (technically / economically)? Technically - very theoretically - yes if the storage tank would be enormous, being able to cover nearly 70 ice days. Economically - no. In a climate like ours (and similar insulation), a tank the size of a small cellar would cover typical heating seasons:
    [2015-01-28] More Ice? Exploring Spacetime of Climate and Weather.

Control, Logging, Monitoring, Optimization, IT Services [Top]

Universalregler UVR1611: Steuerung und Monitoring Wärmepumpensystem

  • I have an issue with the UVR1611 control of my heating system. Can you help?
    We do tailor-made programming of UVR1611-/UVR16x2-based systems and support with setting up and troubleshooting control logic and monitoring. Based on data analysis we help with optimization control parameters, change existing programming, and provide suggestions for making changes to the hydraulic setup.
  • Why have you picked UVR1611/UVR16x2?
    We consider programmable UVR controllers optimized for heating systems. They are not a generic 'smart home' / 'control everything' products but very versatile in relation to the inputs and outputs you need for heating systems. In contrast to all-purpose smart home systems it has features built-in such as control of RPM-regulated pumps.
    New LEO_2 systems are now equipped with UVR16x2 control units (2016-06).
    [2015-03-18] Data Logging with UVR1611 – FAQ.
  • How do you analyze your UVR data? For a quick glance on real-time data, visualization of the current status, or for zooming in on details for troubleshooting we use (free) software Winsol provided by Technische Alternative GmbH. For calculating averages and other key performance indicators we use applications based on Microsoft Excel and SQL Server.
    [2016-12-22] My Data Kraken – a Shapeshifter. The biggest challenge for Kraken is the ongoing change of the ‘database schema’: New sensors, shuffled columns in log files, new calculated values…
  • Is access to the control unit 'via the internet' secure? The data logger CMI is also sort of an ethernet gateway - you can allow visitors 'on the internet' access, but only if they have registered at the vendor's cloud platform. Not recommended: Port-forwarding at your own firewall. An overview on security and different ways of allowing for internet access:
    [2014-11-15] Google and Heating Systems (2).
  • Is there an option to log directly to a custom database instead of downloading log files from the loggers provided by Technische Alternative? There is an open source solution that does just that. As per spring 2015 it only works with BL-NET though:
    [2015-03-18] Data Logging with UVR1611 – FAQ
  • I am curious - how can I sniff the traffic my things (in the the Internet of Things) generate?
    [2014-06-08] Network Sniffing for Everyone – Getting to Know Your Things (As in Internet of Things)
    An example of an issue that might make sniffing traffic on data logger BL-NET's subnet interesting:
    [2015-05-07] Watching TV Is Dangerous.
  • Are you using open source tools and hardware like Raspberry Pi? Yes - we use Raspberry Pi as a CAN bus logger. Since 2016 manually reading off the heat pump's internal energy meter has been automated:
    [2016-08-24] Hacking My Heat Pump – Part 2: Logging Energy Values:
    [2016-08-03] Hacking My Heat Pump – Part 1: CAN Bus Testing with UVR1611.
  • Can the smart grid and power plants be attacked by hackers?
    We can only speculate and try to assess risks:
    [2013-05-13] Cyber Security Satire?

punktwissen [Top]

The 'settlers' have reached the top!

  • Who are you and what is your qualification and expertise? We are two applied physicists, having worked the university, in a research center and in IT. Since 2009 we have been working on our heat pump system in stealth mode, gathering hands-on experience and theoretical know-how. See more details on our About Us page.
    A personal account on the transition from IT back to engineering:
    [2013-01-22] Trading in IT Security for Heat Pumps? Seriously?
  • Do you work with clients you cannot visit onsite? Yes, we do! We started working with home owners in Northern Germany in 2014- using remote sessions (Teamviewer, Skype, e-mail and phone). It works well if you are motivate to build the system yourself or co-ordinate all work to be done by contractors.

This list is updated every 1-3 months. In the 'punktwissen' section of elkement's Blog, you can find all articles on our heat pump system and renewable energy, as well as control and IT - listed chronologically in descending order.

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punktwissen Proyer & Stangl OG, Zagersdorf, Austria
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(Elke Stangl, Sigi Proyer. Last changed: 2017-07-30. Tags: Punktwissen, FAQ, Overview, Heat Pump, IT, Control)