Dear Reader, In case you have arrived at this blog in the middle of the design and build process, you may find it difficult to pick up the threads when I lapse into jargon or acronyms to avoid constantly retyping. Here are a few explanations. I will put in some commercial and Wikipedia links where longer explanations will do better. Please leave a comment at the foot of a blog entry if there is another word you want explaining.

Active House = An extension to the ideal of Passivhaus. Active House implies the acceptance of energy generation technology to ensure that the carbon emission balance gets closer to zero than the Passivhaus. This is especially useful in considering eco-retrofit of existing buildings which cannot be insulated to PH standard. For new build, Active House concept recommends that one tries to build close to Passivhaus standard, but is given more freedom with the design, providing one meets the zero carbon target. Peveril Solar house is meeting that target. See the website.

ArchiCAD = Computer Aided Design software for Building Information Modelling. Inside ArchiCAD is a programming language, GDL (geometric description language) that provides a means to build 3D and 2D objects, and to process data.

Air Source Heat Pump or ASHP = Refrigeration unit that cools the air, and transfers the heat to hot water and a heating circuit for the building. These are the cheapest and most numerous type, and are mostly used as a ‘boiler replacement’ in existing buildings. They are unit construction, that can plug into the house at a convenient location, e.g: near the old boiler position, but being closed boxes, there’s not much to modify on them. They work with decreasing efficiency in the winter as the air cools. There is a noise problem for the neighbours if they are working hard in winter. There is the issue of appearance, in conservation areas, as they must be external and somewhat large. Perhaps options should be available for Timber or Brick patterns to be printed into the metal casing.[Some things that look like ASHPs are actually simply Air heat exchangers, and the actual Heat pump is in the building – this type can be hybridized, e.g: with a ground loop.]


Beaufort Court = The old Ovaltine egg-farm building near Watford that was converted to the HQ of Renewable Energy Systems, a UK based company installing wind farms globally. The complex of buildings is an exhibition piece of experimental technologies, including interseasonal thermal storage.

LinkBeauford Court Website

Bellwire = Thin pair wire that you would use for connecting a doorbell, low voltage. It has a solid copper core.

Biomass = Encompasses the various methods of burning recently grown crops, by direct burning in in a boiler, producing heat and hot water, or conversion to combustible material like pellets or biodiesel. The theory is that if you burn material grown in your own lifetime, it is ‘carbon neutral’, compared with releasing carbon from coal/oil that was locked up in biomass millions of years ago. As biomass can be cultivated and grows annually, it is seen as a good resource, but it has lower calorific value than coal/oil, and in large quantities, can consume large amounts of water, energy and land to grow, and it does emit carbon when burnt. If deforestation occurs to replace with fast growing biomass such as bamboo or palm oil, you have destroyed the previous ecosystem. To grow enough biomass to meet the existing energy needs of the present world population if coal/oil no longer existed would require more than one planet.

Borehole = Drillers use a drilling rig to sink a hole about 125mm diameter, and can lower a pair of 40mm heavy duty plastic pipes with a U-Bend connector at the bottom. Then fill the hole around the pipes with liquid clay so that a good connection is made to the surrounding soil. On the Peveril Solar house, the borehole is a twin pair, reaching down 48m. If you assume theoretically that the annual radius that we are influenced by is 3.6metres, that makes 8,000 metric tons of marl that we draw heat from.

BREEAM = Building Research Establishment Assessment Method. “The leading and most widely used environmental assessment method for buildings. It sets the standard for best practice in sustainable design and has become the de facto measure used to describe a building’s environmental performance.”

Carbon Offsetting = Reducing your own Carbon emission by procurement of energy from a renewable source. For example, the Peveril Solar house has always been ‘Carbon Zero’ if you accepted that by ‘buying’ electricity from the renewable only company Good Energy, it made us less obligated to do anything else to the design. In reality, the ‘ions’ that we use actually come from the coal-fired power station in Ratcliffe, so Carbon Offsetting is a more like a trick than reality.

Carbon Neutral (or Carbon Zero) = means that the energy equation of what you do does not does not cause a net emission of atmospheric carbon. For this, buildings and their occupants must conserve energy (through design, insulation and lifestyle), and generate energy (PV, wind hydro) to balance out what energy they have to use. The Code for Sustainability aims for all houses in the UK to be carbon neutral by 2016, but I consider this to be too difficult for mass market newbuild – individual houses can be engineered this way, but houses in dense urban areas are unlikely to meet all the requirements. Most definitions of Carbon Zero apply this to Space heating, and do not require it to include Hot Water, Cooking, TV, Lighting, etc. The Passivhaus is a more likely standard that the industry will aim for in 2016. By the way, the Peveril Solar house is Carbon Zero for Heating AND for Hot water. See also, ‘Net-Zero’ below.

CHP and Micro CHP = Combined Heat and Power. By running a very economical fuel burning engine, you can generate electricity for export to the building or the Grid, and have a water jacket that removes the waste heat, which can then be used for the building. This technology has leapt ahead in recent years, and can be condensed into units as small as a refrigerator.


Code for Sustainable Homes = Government document setting out a number of step-changes (Code 1, 2, 3, 4, 5, 6) between now and 2016 (and beyond) by which design of buildings can progress towards carbon neutral design. This also includes the improvement of appliances, and of lifestyle patterns such as water use, and management of windows.

Compression Joints = as used in plumbing, joints and devices using a screw thread and nuts for jointing, e.g. flowmeter or water pump – as opposed to Soldered joints.

COP = Coefficient of Performance of a heat pump. Ratio of power used to total heat output. This could be 2, 2.5 or 3, and some manufacturers may claim 4. One way to make this higher is to have an unusually warm thermal mass as the source, which is the reason I have installed a thermal charging system. See also SPF below.

Danfoss = Manufacturer of electrically operated valves for copper piping. There are other manufacturers such as Honeywell, Siemens, but the Danfoss is notable for being suitable for refrigerant.

Datalogger = Electronic box with internal clock, containing a number of contacts to which you can wire a number of thermal and other sensors, and contains a memory for storing the data that comes in. When this data is downloaded to a computer, the software can transform this to a set of graphs or spreadsheets. We were using the DT500. (stands for DataTaker), allowing initially 10 channels for analogue sensors (e.g. recording temperatures), 3 counters (e.g. flowmeters counting accumulated volume or heat energy) and 4 digital (e.g. recording when things are turned on and off)

Delta-T = ΔT ‘Delta’ is normally used to indicate ‘difference’. So it can be used for temperature, pressure, speed, time etc. Delta-T is difference in temperature.

DHW = Domestic Hot Water. This is stored in an insulated tank within the Heat Pump cabinet, maintained at 51.0º precisely.

Energy flowmeter = A device that measures the volume of liquid going through a Flow pipe, but it has a small thermal sensor in it. By placing a matching sensor in the Return pipe, it computes and displays the Kilowatt Hours that have gone through. The one we used is a SuperCal 539 made by Sontex. We are about to change to a Sontex Superstatic 440.

EPC = Energy Performance Certificate. Incentive for house owners to improve the capital value of their asset by improving its energy performance. This is now required for houses being Sold or Let, and includes advice on how to bring the house up to a higher grade. The Peveril Solar house has an EPC for Energy performance of 91 (B++), and an A for environmental emissions. The software doesn’t recognise things like Surya Sunbox, so does not give it credit.

ETFE (Ethylene TetraFluoroEthylene) = is a miraculous and expensive clear plastic that has high strength, high durability and almost 100% transparency. It is three times the cost of glass, but because of its flexibility and strength, an ETFE roof or wall can be a third of the cost of glazing if you consider self weight, resilience and the complexity of equivalent metal glazing systems. It’s the external cladding for the Eden centre and the Leicester Space centre, the Beijing Aquatic centre and Munchen’s Allianz arena. Nobody knows how long it lasts, as no ETFE installations have degraded yet.

EvoEnergy = Solar power company, based in Nottingham, who supplied and installed our Photovoltaic system, and the web router enabling our roof to datalog to the Internet.

FIT = Feed in Tariff. System by which users of renewable technology will be rewarded by beneficial subsidies based on performance.

FLEQ = Full Load EQuivalent hours of running. Its jargon used in the Heat pump industry, and simply mean the number of hours that the heat pump is running in active heating mode. It is found by dividing the number of kilowatt hours used by the machine in a year, divided by the power it uses on full load. It was over 2000 for our machine in 2009-10, but since the installation of Surya boxes, is down to about 12-1300. Or simply read the system clock! This factor is used in determining the depth of a borehole, calculating the amount of energy and how frequently the borehole has to deliver energy to the ground loop. (when the GSHP is not in heating mode, it sits there checking the thermal sensors using only about 11 watts which is negligible).

GDL = Geometric Description Language, a parametric programming language working within Graphisoft’s ArchiCAD, for 3D and 2D modelling of components. It is also capable of reading and processing data, e.g. for thermal modelling.

Glycol = Is the popular name for Anti freeze, mixed about 1:3 with water, and circulated between Sunboxes, GSHP and Borehole as a refrigerant. Although working temperatures are normally above freezing, there are times in winter when the system is not active (night time), but a deep frost can affect the external panels if not protected with anti-freeze.

Good Energy = Electricity supplier who guarantee only to sell as much energy as they can buy from Windfarms, solar, hydro and home generators. Using a supplier like this is, in effect, ‘carbon offsetting’. We have been using Good Energy since 2006.

Ground Loop = The circulation of antifreeze from the heat pump, down to the deep ground and back – in our case, the loop splits into twin holes, and is rejoined when it returns. Our sunbox loop is simply tee’d into this and diverts some of the liquid to solar collectors on the south wall. Ground loops can be horizontal or vertical. Pipes from the Heat Pump can descend vertically in boreholes to reach thermally stable depths of 15, 50 or 100 metres depending on the predicted demand of the building. Pipes can be laid out horizontally under a lawn or paddock, 1-2m deep in pipe meshes or loosely laid curvy pipes in a trench, to benefit from ground that is close enough to the air to be affected by seasonal change.  In the Peveril Solar house, we have twin boreholes, 5m apart, 48m deep.

Ground Source Heat Pump or GSHP = Refrigeration unit that cools the energy source (ground), and transfers the recovered heat to hot water and a heating circuit for the building. Reverse cycle HPs enable cooling of the building and warming the soil, in summer. These are mostly fitted in newbuild construction, due to the excavation works. Our GSHP is not a reverse cycle, but it does have an integrated DHW tank. The management system of the GSHP monitors internal and external temperatures, flow and return of the heating circuit, and calculates when to come on for a heating cycle, and when to go back to dormancy.


HIP = Home Information Pack. This is the key to making eco-design cost effective over and above mere energy savings – as you will get money back in the higher capital value of the house. This was, unfortunately, abandoned in May 2010.

Hysteresis = An acceptable amount either side of a target. e.g. 5 mins early or late for an appointment is OK, 10 mins is annoying. For air temperature, 2 degs C either side of a target is acceptable, less than this we turn on the heating, more, we open a window! If thermostats activate precisely when a temperature is reached you can get oscillating operation, called ‘hunting’. A time delay or temperature hysteresis allows systems to settle down.

Ice Energy = Leading company in the UK heatpump market that import, supply and support users of ground source and air source Heatpumps. Also support research into innovative uses of heat pumps, such as in the Peveril solar house. Partial sponsors for this project, by supplying some of the control and monitoring components.

IVT = The Swedish company who make the Greenline heatpump that we use. The C6 model in our house is a combination model, with the watertank incorporated in the same cabinet as the heatpump mechanism.

kWhr or kWh = Energy quantity: Kilowatts of power multiplied by Hours. This is a universally recognised unit for energy, and can be used for electricity, gas, thermal storage and more.

Monodraught = company who have pioneered the recent evolution of Suntubes, bringing sunlight deep into buildings, and we have one of these!

Mirrors = in the context of this blog they sum up the use of brushed aluminium reflectors, acting as solar concentrators around the sun boxes, or around windows. They are not optically clear mirrors.

Navitron = A supplier of renewable energy products, with a strong niche in the market for self build or small business installers. They also maintain the Navitron forum, which is the most highly informed chatting location for amateurs in renewable energy technology. But beware, commercial participants are not welcomed, and if you start spouting off on this and that, you will be rapidly corrected by experienced people who know more than you do, or most likely banned from the forum by malicious and bigoted moderators who don’t seem to be prepared to learn anything beyond what think they already know!

Net-Zero = is similar to the Active house concept, whereby if the metered energy inputs and outputs of the building result in zero or even an energy credit, then the building is Net-Zero. It becomes very difficult to compute if the building’s heating is supplemented by wood-burning stoves and the like. this does not mean the same as being Off-Grid. The grid and the earth can be used for storage, and one balances the annual figures. In the case of the Peveril Solar house, it is easy, Metered Energy to the GSHP and Metered Energy from the PV roof – they are in a credit balance – better than Net-Zero.

OfGem = Ofgem is the Office of the Gas and Electricity Markets. OfGem is committed to protect consumers – by promoting competition and regulating the monopoly companies which run the gas and electricity networks.

Passivhaus = Design standard for dwellings for passive design and orientation, extreme insulation and energy efficiency, employing great air tightness with whole house ventilation. It is the world’s leading standard in energy efficient construction, pioneered by the German physicist, Professor Wolfgang Feist. There are already 7-10,000 houses built to Passivhaus standards in southern Germany, Austria and Switzerland. In the UK, there are some singly built examples, but it is doubtful if there are any yet built by any mass market housebuilder. This is the standard that is likely to be adopted by the UK for 2016, as it is more attainable than the rather vague ‘carbon zero’ (compare this to the Active House concept).


Pasteurisation = means boosting the domestic hot water tank to 61º or 62º C, about 11 degrees more than the usual desirable temperature. This is a safety precaution, in case Legionnaires’ bacteria have had time to grow in the tank.

PCM = Phase Change Material – something like Wax or Ice or thermal Salts. PCM takes advantage of the latent heat of a change of state, such that if you put heat into it, or take it out, it does not change temperature even if you pump more in, until it is all changed to another state, eg melted. This can be a great benefit eg if the container does not get hot, and therefore it does not lose heat to the surrounding. It also releases heat slowly. Midway in the project, I considered using a tank full of PCM spheres, but later decided to store them for a future project.

Polycarbonate = A thermoplastic polymer, looks like Glass, but it can be cut, bent (slightly), drilled. Sometimes referred to as “Lexan” as that is the most famous name brand of polycarbonate.

PV, Photovoltaic = Photovoltaic – making electricity by the action of sunlight on silicon wafer.

PVT = Photovoltaic Thermal combined. I have great faith in these for the future, but only if linked to Underground Thermal Energy Storage, or direct loops from a heat pump. For heating hot water, they are the wrong technology.

Pyranometer = Device used to measure solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density (in watts per metre square) from a field of view of 180 degrees.

Rushcliffe = The District / Borough Council in which I live, incorporating West Bridgford.


MapGoogle Maps

SAP = Standard Assessment Procedure, for checking on the CO2 emission of a house by calculating all its surface areas, heating system etc.

Screwfix = Trade/Retail Supplier with branches all over the company, retailing electrical, joinery, workwear, tools, building and plumbing products to the trade and to the public – with an excellent catalogue and website.

SPF Seasonal Performance Factor = variation in the COP of the heat pump depending on the balance between heating demand and energy levels available at different times of year, and finally computed over the length of the year. If during Equinox, the energy levels lead the HP to perform as if it is Summer, and if during Winter, the HP performs as if it is Equinox, then that will show up at the end of the year as a very good SPF.  It is one of the aims of the project to use solar earth charging to improve the SPF of the heat pump by boosting the energy level of the source.

Solar Fraction: I am occasionally asked how we make the claim to be ‘solar heated all year round’ and that can be explained with the concept of ‘solar fraction’ – comparing what power we can capture from the sun with what we need to provide heating and hot water. Typically we are averaging 120% over the first 32 months of the Sunbox installation. In doing this calculation, I am simply looking at metered quantities: Electrical Energy we can generate annually divided by Electrical Energy we must use to heat the house and hot water.  There are some interpretations of Solar Fraction, but if you Google the expression, this seems to be the most frequent answer. As an electrically heated house, it is possible to read the meters, deduct from the previous year’s reading and then calculate the solar fraction precisely to a decimal point. We do not have biomass boilers or wood burning stoves to confuse the issue. Of course, we are getting thermal energy from the ground (which comes from long term solar originally). The whole point of using a Heat pump is to have a coefficient of performance that is better than 1:1 heating. It’s classed as a renewable technology because it is drawing heat energy from a renewable source.

‘Encyclopaedia of Alternative Energy and Sustainable Living’

Sunbox = A solar panel that is larger and deeper than a normal panel, so that the air volume inside gets warmer than the surrounding air – warmed by solar radiation, cloudy bright conditions, or just by being out of the wind – so a thermal collector inside can collect heat by day or even at nighttime.

Solar Oven (or Cooker) = Low cost insulated box, mat black on the inside, with a glass cover and surrounded by metallic bright reflective planes, to increase the heat inside.

Surya = Hindu god of the Sun. Name used for the Sunbox Mark One and Mark Three and Mark 4.

Savita = Hindu god/goddess of the Sun (name is applied to either gender). Name used for the Sunbox Mark Two.

Stack Effect = the way in which warm air tends to rise, evident in Cumulus clouds, Chimneys, Hot air balloons, double skin facades, structures with glass roofs, etc. It can be exploited productively, to use the updraft to pull cool air into a building at low level.

Thermal Collector = A panel through which you can flow cool liquid, thus picking up heat from the air or sun. This can be Plastic or Metal. In the context of the sunboxes, I sometimes refer to them as ‘Chillers’ as they are doing just that to the airspace in the sunbox.

Thermocouple = Temperature sensor based on bi-metallic wire meeting at one point, e.g., taped to a pipe, and linked back to a data logger.

Thermal Storage, Diurnial = Storing heat during the day that can be used later during the evening and night.

Thermal Storage, Interseasonal = A means of storing Summer heat (usually Solar), long enough in a medium large enough for it to be used during the Winter.

Thermal Storage, Real-time = Putting heat/power into a storage medium that is immediately used by the device, similar to using your laptop while plugged into the mains.

Thermostat = Measures temperature and triggers an action. The AKO 14723 that we use is capable of activating on a difference of temperature between sensors, or highs and lows, with two distinct channels. It is programmable and can be wired up to activate light indicators, valves, clock, data loggers and pumps etc.

Thermistor = Temperature sensor using a tiny resistor, that can more easily be connected by bell wire to a thermostat.

‘Trickle’ = Circulating glycol through the Sunboxes at about 5 litres/minute using the low power consumption pump in the loft.

‘Whoosh’ = Circulating glycol through the Sunboxes at about 18 litres/minute using the circulating pump in the heat pump.

‘Trickle-and-Whoosh’ = Plumbing in series arrangement with a 3 port solenoid valve so that when the Thermostat and the GSHP both say Yes! The Entire ground loop is diverted sequentially through the Sunboxes at 15 litres/min, downloading any heat very quickly, chilling the sunboxes quickly, and then the thermostat says No!, allowing the valve to close again, and turn off the loft pump. It reduces pump power consumption, but is activating the solenoid valve too frequently. This is only possible if the pipe sizes are large and the black collectors support fast flow. Over the length of a day, the total thermal capture is similar to Trickle all the Time, but collected in intermittent pulses. When the heat pump is dormant and the thermostat says Yes! A small 30W pump moves the glycol slowly around the loop at about 5 litres/min. A disadvantage is that if there is a fault with the wall or roof mounted solar panels, the entire system is down, including the heat pump, which could be a risk in winter. This is what we used on the Peveril Solar House, May 2010-March 2012.

‘Trickle-all-the-Time’ = Plumbing in parallel arrangement so that the loop through the Sunbox is a parallel bypass to the existing ground loop, working at 5 litres/min and is controlled by a 2 port solenoid valve. This circulates whenever the thermostat says Yes! When the heat pump is running a heating cycle, the Sunbox loop merely injects the warmer fluid at 5 litre/min into the fast 18 litres/min flow, meaning that the thermostat sees a favourable delta-T for far longer, saying Yes! For 3 or 4 times longer perhaps. This enables one to use narrower pipes and narrow diameter metal collectors, but will cause longer hours of pump consumption. 
 A non-return valve is required to make sure that the circulation goes in the right direction, not making a closed circuit.
One advantage is that the thermal capture is easier to Meter. The comparison of temperatures of two pipes is difficult at any time, but if the difference is only 1 or 2 degrees, a meter can get it wrong. With a slower flow of 5 litres/min, the temperature difference is more significant and the meter reading is more accurate.

Trigger Sensor = A thermal sensor that is used by the thermostat to turn on a device, such as a pump.

Trombe Wall = Combination of a dark (heat absorbing) wall with a glass front to retain the heat from solar or infrared sky radiation. The rising hot and dry air can be used to warm a building.

Tundish = A small funnel that allows liquid in a plumbing system to be caught and transferred safely out of the house.

WSHP = Water Source Heat Pump

Water Source Heat Pump = Heat Pump unit that cools a nearby water source, and transfers the heat to hot water and a heating circuit for the building. Pipes from the unit can use a lake, reservoir or river. There are legal issues, e.g. whether there are public using the river or lake, using canal boats or anchors, whether British Waterways board or others own the water, whether your pipes would have to cross other people’s land to reach the water, how localised cooling will affect the ecosystem. Running water in a river is better than canal or lake, but will they shift the river bed in stormy weather and expose your pipes, or even drag them down river? Some WSHPs can have pipes descending vertically in a borehole to underground water. WSHP is so rare that it does not rate an entry in the Energy Savings Trust website or Wikipedia.


Wilo = Manufacturer of water pumps as used for central heating. There are other good makes, such as Grunfoss, but the Wilo is notable for being more suitable for refrigerant.

UTES = Underground Thermal Energy Storage, the expression used by Nic Wincott and others to describe what I call Solar Earth Charging.

University of Nottingham = one of the UK’s leading universities, and ranked in the top 75 in the world. The Department of Architecture and Built Environment has a major role in the area of Sustainable Energy Technologies, with many PhD students, ecohome projects, masters courses etc.

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