Heat Pumps and Renewable Energy

Our heat pump system uses an underground water tank and a solar collector as a heat source. This blog has been my way of publishing our research.

Page last edited: 2019-05-10.

Solar/air collector in January 2017

[2019-01-18] Modbus Server on Raspberry Pi as Babelfish for UVR16x2. A nice-to-have extension to the existing control infrastructure. As the CMI has a Modbus interface it can log data from a Modbus server running on Raspberry Pi, and this Modbus server can forward data from other loggers as a ‘protocol translator’ and provide values derived from calculations.

[2018-09-24] Heat Conduction Cheat Sheet: Temperature waves – simulating yearly and daily oscillations in the temperature below the surface of the earth or near wall/floor of our ice/water tank. Stationary solutions – to assess the heat transport between pipes and the medium they are immersed in, like the tubes making up the heat exchanger in the tank or the solar/air collector.

[2018-06-10] Infinite Loop: Theory and Practice Revisited. “Whenever I used knowledge to achieve a result that I really needed to get some job done, I think about this knowledge as emerging from hands-on tinkering and from self-study (no matter if I also have formal education”. Meta thoughts on engineering and more…

[2018-04-09] Can the Efficiency Be Greater Than One? This is one of the perennial top search terms for this blog. Anticlimactic answer: Yes, because input and output are determined also by economics, not only by physics.

[2018-03-03] Consequences of the Second Law of Thermodynamics. Mulling upon theory – Carnot’s efficiency again. Most textbooks introduce Carnot’s cycle by calculating energies for an ideal gas – but the efficiency would not change if the substance was not ‘ideal’ in the sense that the equation of state – p(V,T) – were different.

[2018-01-19] The Heat Source Paradox – a simple relation between a heat pump system’s key data; yet used in a misleading way in adverts: The worse the performance is, the smaller the heat source can be built.

[2018-01-12] Things You Find in Your Hydraulic Schematic. I am starting the New Year of Engineering Blogging at a lighter pace – don’t expect too much content this time!

[2017-12-13] Cooling Potential. We had an interesting discussion about the cooling potential of our heat pump system – in a climate warmer than ours. So we started to think about improving cooling power, by adding active cooling functionality.

[2017-11-28] Simulating Life-Forms (2): Cooling Energy. I found an incredibly detailed research report by the Australian government – about energy use in private homes, by appliance and purpose. It confirms my reluctance to ‘predict’ cooling energy as usage of air conditioning depends strongly on life-style choices.

[2017-11-01] The Collector Size Paradox. Results and data for 5 heating seasons. Emphasis on data/tests and ‘theory’/simulations for the impact of changing the size of the solar/air collector.

[2017-10-12] Data for the Heat Pump System: Heating Season 2016-2017. The usual number crunching – performance, energies, temperatures, ice – plus a summary of the system’s configuration and ‘cultural’ context. Also presenting data on passive cooling.

[2017-09-17] Tinkering, Science, and (Not) Sharing It. That moment when you realize that your tinkering with PVC piping is actually science.

[2017-08-17] Simulations: Levels of Consciousness. Getting philosophical – what is a simulation (of our heat pump system), and what are the challenges? For modern buildings, simulating ‘user behaviour’ can be as critical as simulating ‘physics’ and control logic.

[2017-07-14] Heat Transport: What I Wrote So Far. A list of all my blog posts focussing on heat transport, plus short summaries: Heat transfer and energy storage in our heat pump system, in ground, in ice. Analytical solutions versus numerical simulations versus maverick’s heuristics.

[2017-05-02] Simulating Peak Ice. Continued from last post – comparing measurements of the level in the tank with simulations of the evolution of the volume of ice. Simulated maximum volume is just 0,7m3 greater than the measured volume, and the true plateau of ice (for about two weeks) is modeled correctly.

[2017-04-08] Mr. Bubble Was Confused. A Cliffhanger. Tales of a level sensor: In the coldest January since 30 years Mr. Bubble ware driven over the edge. He had to deal with a cliff … of ice.

[2017-03-18] Where to Find What? A list of lists – our web resources related to the heat pump system: Data, brief explanation, FAQ, this list of postings here.

[2017-02-22] Ice Storage Hierarchy of Needs. Why the maximum volume of ice obtained in a season depends sensitively on the properties of ground and the collector.

[2017-02-05] Earth, Air, Water, and Ice. Data analysis of the heating season 2014/15 (when we turned off the solar/air collector to simulate a harsher winter). From the net energy ‘in the tank’ the contribution of ground can be calculated. Data also show that the collector is delivering the more energy the colder the tank is.

[2017-01-20] Frozen Herbs and Latent Energy Storage. From root cellar to heat source … using pond liner. Sort of step-by-step instructions, using an every day analogon.

[2017-01-07] On Photovoltaic Generators and Scattering Cross Sections. A physicist’s musings about the unit used to characterize solar panels’ peak power: kWp.

[2016-11-03] And Now for Something Completely Different: Rotation Heat Pump! An invention – an answer to: Can a compression heat pump be built in a completely different way?

[2016-10-21] Same Procedure as Every Autumn: New Data for the Heat Pump System: Similar results as last year, minus special research projects but plus a bit of nostalgia – when celebrating the 4th anniversary of starting up the system.

[2016-09-18] Re-Visiting Carnot’s Theorem. From the theory department: Why can’t there be any heat pump / heat engine better than Carnot’s reversible machine? A closer look at the proof by contradiction.

[2016-08-24] Hacking My Heat Pump – Part 2: Logging Energy Values: Connecting Raspberry Pi CAN bus logger to the Stiebel-Eltron heat pump and querying for temperature and energy values.

[2016-08-03] Hacking My Heat Pump – Part 1: CAN Bus Testing with UVR1611. Extending logging infrastructure – automating reading off our heat pump’s internal energy meter by using Raspberry Pi as monitoring device. Before connecting to the heat pump hardware and software is set up and tested with a CAN bus I am familiar with.

[2016-06-22] First Year of Rooftop Solar Power and Heat Pump: Re-Visiting Economics. Monthly statistics: Energy ‘generated’ by the PV panels, fed into the grid or supplied from grid, consumption in the house and by the heat pump in particular. 30% of total energy consumption was provided directly by the PV generator (no battery).

[2016-06-01] Photovoltaic Generator and Heat Pump: Daily Power Generation and Consumption. Comparing detailed time curves – illustrating why it is hard to raise self-consumption and self-sufficiency above statistical averages for homes without heat pumps: PV output, input energy for the heat pump’s compressor, and the home’s total smart meter balance.

[2016-05-19] Everything as a Service. Trying to predict the not-to-distant future of heating for consumers – following the ‘as a service’ philosophy introduced to software products long ago: Heating will be turned into monthly subscriptions bundled with internet access and bank accounts, and home owners will host aesthetically pleasing black-boxes operated by ‘platforms’.

[2016-04-15] Alien Energy.

[2016-02-08] No, You Cannot ‘Power Your Home’ by One Hour of Cycling Daily. You need to get a feeling for numbers ‘in renewable energy’ – and it more than baffles me when authors of click-bait articles don’t bother to the most basic cross-checks. It seems we lost the feel for ‘what can power what’ when engines replaces horses and humans.

[2016-01-22] Temperature Waves and Geothermal Energy. For our numerical simulations of the heat pump system (estimating the maximum volume of ice, for example) we need 1) to make an assumption for the thermal diffusivity of ground, to calculate heat transport between the ice storage and ground, and 2) find a simplified way of accounting for the solar energy deposited near the tank. For both purposes, it is interesting to have a look at the evolving of temperature in undisturbed ground, governed by the Heat Equation. This is a post in my capacity as the ‘Theory Department’.

[2016-01-07] How Does It Work? (The Heat Pump System, That Is) The reply to numerous questions like: Can you explain – using images, with an animation – how the combination of ice/water tank and solar collector works? Here is a slide-show of operating statuses throughout a typical year.

[2015-12-07] Half a Year of Solar Power and Smart Metering. Also including daily and monthly balances of electrical energy, showing the amount of energy used by the heat pump’s compressor versus energy consumed by appliances and control.

[2015-11-25] Peter von Rittinger’s Steam Pump (AKA: The First Heat Pump). An account of the 19th century invention, based on the original German research reports.

[2015-11-13] The Impact of Ambient Temperature on the Output Power of Solar Panels. Verified by analyzing our monitoring data – combining logging from our heat pump’s control unit (UVR1611) and the PV inverter’s logging.

[2015-10-14] Economics of the Solar Collector. My reply to an interesting question on measurement data for last season: Why invest in a solar collector if the performance factor decreases just a bit if you turn it off? Performance would not have been that high after turning the collector off hadn’t we used the collector for months before.

[2015-09-29] Heat Pump System Data: Three Seasons 2012 – 2015. Brief summary of last season’s performance, plus back-of-the-envelope estimate of economics: Heat pump versus natural gas, based on costs of energy in Austria.

[2015-08-11] Having Survived the Hottest July Ever (Thanks Natural Cooling!)

[2015-07-15] Solar Energy, Batteries, and Autonomy. Third post on our PV generator – with data for the first two months, and my personal assessment of using battery storage.

[2015-06-17] Solar Power: Some Data for the First Month. Figures and numbers from our PV generator’s logging: Efficiency of solar panels decreasing with temperature, intermittent short and very high power spikes, and daily energy balances (consumption / generation / grid).

[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’. The rather high factor gives proof of the fact that heat pumps operate well above absolute zero.

[2015-05-18] Two Weeks After Lift-Off. An update on our photovoltaic energy generator: safety features, startup, and data for the first two weeks. Currently about 55% of the energy consumed by appliances and the heat pump come directly from the solar panels.

[2015-04-21] How to Evaluate a Heat Pump’s Performance? Definitions of performance indicators and how to determine them – comparing alternative methods, based on sensors available (COP from temperatures versus Performance Factor from energy readings).

[2015-04-01] Ice Storage Challenge: High Score! At the beginning of February we had turned off the solar collector to mimic a harsher winter. The ice cube, generated by our heat pump since then, stopped growing at about 15m3. About 10m3 of water remained unfrozen. After a few days in this steady state we turned on the collector again and resumed standard operations.

[2015-03-23] We Have Come a Long Way: Rooftop Solar Power Now! We had rebuilt half of our house but not installed solar panels – until recently. Here are some photos and a back-of-the-envelope assessment of economics of PV (in Austria); so now we harvest both energy inputs for the heat pump: Ambient and electrical energy.

[2015-03-18] Data Logging with UVR1611 – FAQ. What I would have wanted to read when I once made myself familiar with the freely programmable controller. I am responding to several, similar questions in this post.

[2015-03-08] The Ice Storage Challenge. We switched off the solar collector at the beginning of February “for research purposes”. This is the status report!

[2015-02-27] “An Unprecedented Test for Europe’s Electricity System”. Solar power and the impact of a solar eclipse. Soon we will contribute – our PV generator has already been ordered.

[2015-02-14] A Sublime Transition. Phase transitions between water, vapor, and ice: Last winter’s viral trend of freezing boiling water in mid-air, and discovering that scientists discuss such effects to this day.

[2015-01-28] More Ice? Exploring Spacetime of Climate and Weather. A simplified simulation based on historical weather data: How big should the ice / water tank (used as a heat source) be?

[2015-01-22] Personal Risk Assessment. The previous post on our ice-storage powered heat pump triggered an interesting discussion about the risk of a power outage. Is it more risky to pick a heat pump – compared to other systems?

[2015-01-15] We Want Ice! Current measurement data showing the formation of ice in the ‘ice storage’ water tank. Winter is mild here, so there was only 1m3 ice so far. But we might partially deactivate the collector to test the generation of a bigger ice cube.

[2014-12-14] Cistern-Based Heat Pump – Research Done in 1993 in Iowa. I stumbled upon a research report that described a heat pump similar to ours – except for the fact that the authors considered the collector not essential, based on a crude steady-state estimate of the heat flow from ground to the tank. Pionieering work though as they built the solution incl. data acquisition from scratch.

[2014-11-29] “Being Creative with What Is Available” – this refers to playful tinkering in general, and to building solar collectors and ice storage systems for very special buildings.

[2014-11-15] Google and Heating Systems (2). Again the Internet of Things! One of my favorite things is the data logger for our heat pump system and gateway between CAN bus and ethernet – C.M.I. by Technische Alternative. Plus some consolidated research on how Things phone home, and my rants on not using passwords with internet-facing systems.

[2014-11-08] A 1970s Pioneer in Self-Sufficient Living. This is about heating power from compost and not even tagged with ‘Heat Pump’ – but nonetheless I can relate to Jean Pain’s ideas. I know what it means to be driven by the quest for self-consistency in your life-style choices, your hobbies, and in the way you work.

[2014-10-04] Pumped Heat from the Tunnel – my summary of a press release that announced a EU ‘Smart City’ project. I focus on using water from an infamous tunnel as heat source of a heat pump.

[2014-09-28] Biology / Chemistry Challenge or: Should We Really Blame the Dead Frog? Normally, the water in the tank does not need to be drained or replaced. Except: You started pesky anaerobic reactions as you feed the bacteria in the water too much brine.

[2014-09-07] Big Data, Big Plastic Worms, and How to Utilize Your Cellar: An update on the status of our heat pump system – the solar collector has been overhauled – and looking back with nostalgic feelings! What you never wanted to know about small houses and their earth cellars in Eastern Austria.

[2014-07-03] What Learning about Feynman’s Path Integrals Was Good for. On the arcane nature of pipework and its documentation.

[2014-05-31] Art from Plastic and Wood: Some pictures of a solar collector built for a client. The water tank is located beneath the garage, and the solar collector installed on top of it. This is a condensed cross-post of a series of posts published to our German blog.

[2014-04-13] Measurement Data for Our Heat Pump System – Finally Translated Documentation: This document also includes a more detailed description of the system and some configuration parameters.

[2014-02-20] Lost in Translation – an Overdue Update: Short overview and bold announcement of more technical documents to be translated to English.

[2013-09-04] Greatest Innovation Ever: Thoughts on the power grid – tangentially related to heat pumps that are often considered sort of buffer that will help to stabilize the smart grid (via demand side management).

[2013-08-14] Welcome to the Real World! Actually an away note from my social media break – but also showing off our tomato plants, attached to the solar collector used as an espalier. I’ve included brief information on the operations of the collector in winter versus summer (cooling mode)-

[2013-02-26] Controlling the Four Elements. Or: Why Heat Pumps Are Cool: Hydraulic design and short overview of our heat pump system that uses a water tank (‘ice storage’) ‘powered by’ an unglazed solar collector as its heat source.

[2013-01-22] Trading in IT Security for Heat Pumps? Seriously? More of a personal essay on my career transitions, including a small section on the system.

[2012-12-10] The First Heat Pump Ever Was Built in Austria: History on engineering – set in my home country.

[2012-05-10] Why Do Heat Pumps Pump Energy so Easily? Brief (yes, really) explanation how a heat pump works.