Wednesday, December 22, 2010
The houses were built in 1905, and at that time it was standard practice to share a water connection between houses - especially if they were pairs of semi-detached properties. So it came to pass that four properties were all connected to the one section of lead pipe - and after 105 years in the ground, that lead pipe was leaking like a seive.
Back in July, during leakage testing, an excessive flow was detected on our shared main, and since the old lead main is no longer accessible as it passes under driveways, patios and modern extensions, the only effective measure is to replace the shared main with a separate modern plastic main and meter for each property.
The crew from the water company turned up at 8am on Tuesday and started to dig a couple of trenches, one near the pavement and one close to where the main would enter the property. Using a pneumatic mole, a duct was bored through the soft clay soil to connect the two trenches - a distance of some 15 metres. However because of very cold conditions yesterday, the Mole froze up in the bore, and had to be retrieved by digging a third hole, just 2m short of the pavement excavation. With one bore in place the blue water pipe was threaded through and the Mole set up again to put a second bore through for my neighbour's pipe.
Today the gang have got extra help from another 3 crews, judging by the 4 large vans in the street. The main runs down the road on the opposite side of the street, and so 4 separate access pits will have to be dug on each side of the street, and individual plastic connections tee'd into the original main. A lot of digging in temperatures that are barely above freezing.
Thursday morning, and Day 3 of the Big Dig. Two gangs from Clancy Docwra accompanied by another private contractor who's turned up with another compressor. About 11:15am, the water company arrived to assist with the pipe connections. It should not go unmentioned that replacing the water mains to 4 adjacent properties is no small undertaking, and made particularly gruelling in such bitterly cold weather. Whilst to the homeowner, the pipe from the pavement to their kitchen might at first appear a major task, this is actually only one small part of the job, and the connections to the water main on the opposite side of the street each with two access trenches is by far the bulk of the work.
Inside the house, in the kitchen extension, the dishwasher was removed to gain access, and a 32mm hole drilled downwards and outwards through the kitchen wall, such that the drill emerged in the small connection pit outside the kitchen window. This is a busy area in the kitchen with heating pipes, hot and cold water pipes and cables all laid in a ductspace that runs around the external wall of the kitchen. It's now a case of connecting up to the incoming main to ensure that the kitchen, bathroom and toilet, and the rising main to the tank in the loft are all connected to the new supply. The plumbing in this house dates back in various phases back to 1905, and much of it is no longer accessible, having been laid under the concrete floor of the kitchen and the 1950's bathroom extension. Once everything is working properly from the new main and no leaks detected, the old lead and copper connection can be isolated and left in the ground as a bit of ancient history.
I must say I am very impressed with the teams that have worked outside in miserable conditions, and temperatures barely above freezing. Sutton and East Surrey Water who did the work within the boundary of the properties and Clancy Docwra who undertook the excavations and connections to the main in the street. Whilst £900 is quite a large sum to find just before Christmas for replacing a main, when you look at the effort involved with up to 6 people on site for 3 days, it is clear that it is justified when you see the effort and comittment involved.
Monday, December 20, 2010
1. Smart Relay unit retrofits in place of existing time controller - no changes to mains wiring
2. Uses a hand held combined display and programmer/thermostat connected via wireless link
The hand held display/thermostat allow the thermostat to be located in whichever room you spend most of your time in. In most homes this would be the living room for the evenings, but if you work from home, you may choose to have the thermostat in your work room or home-office during the day. Portability means flexability. If you are wanting to reduce fuel bills by partial heating of a property, best that you focus the heat and the temperature control into the room that you are most likely to be occupying, and let the thermostatic radiator valves prevent excessive temperature in other rooms.
Regardless of where you choose to site your thermostat it will communicate via a wireless link to the relay unit which controls the central heating and hot water circuits. As a display unit it will offer you real time display of your energy usage (similar to an electricity monitor) and also an efficiency indicator and an indication of mean outside temperature.
Low Cost Zone Heating.
Back around 2005, I discovered that you could use a small amount of heat applied to the wax cartridge of a thermostatic radiator valve, which would cause the wax to expand and shut off the valve. I experimented first with power resistors and then power transistors and found that approximately 1W of dissipated power would completely close a thermostatic valve in 15 to 20 minutes. It would therefore be possible to have a controllable resistance fitted to each radiator's thermostatic valve and shut down individual radiators when they were not needed. It would only take about 10W of electrical power to shut off 8 radiators and this could be done as a low voltage (24V) signal distributed along cable, such as telephone extension leads. When the boiler is not running, the valve control resistors would not have to be energised, allowing further economy.
For this to work well, the controller would have to pre-anticipate when it was due to turn the boiler on, and open the valves some minutes in advance. It would make sense to use a long boiler on time and off-time, so that the latency of opening the valves is insignificant compared to the boiler on times. A longer boiler on-time could be achieved by turning down the boiler water temperature, so that it heats more slowly. This would also have the benefit that the return water would be close to 50C so that the boiler works in condensing mode most of the time. Additionally by increasing the hysteresis from say 0.2 to 0.4C would double the boiler on time. In an ideal world, the boiler would run continuously at what ever kW output was needed to maintain the set temp, however this may be difficult to achieve with a 24kW boiler in a property that really only needs a 12kW unit.
The boiler output temperature will be a function of circulation pump speed. By dropping the circulation pump to the lowest speed, the boiler will lower its output accordingly. This can however be counter-productive, as some tests proved. A combination of low pump speed and low water temperature means that the radiator barely gives out enough heat to satisfy the room temperature demand of the thermostat, so the boiler runs for very extended periods at low power. Ironically this can lead to the use of more gas, than if it were allowed to run for say 30 minutes and then coast, until the lower hysteresis level of the thermostat.
Building on the above idea, another control strategy might be to have a fixed on period of say 30 minutes, allowing the temperature to rise, if necessary, above the upper hysteresis point and then turn the boiler off until the room temperature fallss below the lower hysteresis point. A small amount of temperature overshoot will not be noticed, and this strategy will lead to a decent length of on time and a longer off time.
This is usually performed with readings from an external temperature sensor, which allows the output of the boiler to be controlled in response to outside temperatures. For example, in cold weather, it might be desirable to bring the boiler on for longer if certain temperature conditions are required by a certain time. Similarly, in a property with high thermal mass, the boiler could be turned off earlier, for example in the late evening, if it is known that the night is milder and heat loss will be reduced.
With the Christmas break plus daily cold weather, I hope to code up some of these ideas on my Arduino mega based heating controller, and try them out.
First, here's the warmup from nominal 17C to nominal 19C on Sunday morning. This took 4 hours and used 50kWh of gas. In each of the following plots the x-axis is the time in minutes.
At the same time the outside temperature was rising from about -4 to about -1C - but more importantly to the controller, was the difference between inside and outside temperature - the Delta temp. As you can see the delta temp was between 20 and 21.5 C for all of the warm up period.
By 10am the room had come up to temperature and the controller enters the second phase - main room temperature at a comfortable 19C +/_ 0.2C.
The next set of 3 plots shows the detail from 10am Sunday to 10am Monday. This was the coldest night so far with temperatures down to -9.3C! Note how the delta reaches a maximum of 29. In real terms this means that the heating has to work about 50% harder, than if delta is about 20 - and thus use a lot more gas.
Below is the plot of the room temperature, once the system had stabilised, holding the room at 19C +/- 0.2C. Each little sawtooth is the effect of the boiler coming on at 18.8C and heating the room up to 19.2C - this maintaining an average temperature of 19C.
Saturday, December 18, 2010
The nights of 17th and 18th December were without doubt the coldest nights so far this winter with suburban Surrey temperatures dropping to -6C.
As I write this we are experiencing a second wave of Arctic winds bringing temperatures down well below zero, large flakes of snow settling on an already frozen ground. More chaos due on the roads and airports, just 3 weeks after the first blast of winter that caused widescale disruption to transport and infrastructure.
In Britain we have the awkward situation that we do not get severe winters each year, so little is done in advance to prepare us for wintery weather. Much of our older housing stock was built with very poor insulation, and the time has come to upgrade the older houses with measures such as draught-proofing, adequate loft insulation, double glazing, more efficient condensing gas boilers and ultimately whole house external insulation.
Now whilst it may be possible to reduce heating gas consumption by 25%, in an older property with no cavity with a suitable thickness of external insulation, the cost of this upgrade will run to appproaching £10,000. With a current gas consumption of just £500 per year, a saving of £125 per year and with an 80 year payback time make the expense of external insulation seem barely worthwhile. However, the price of gas has trebled in the last decade, and if it continues to follow this trend, or just double with each decade, it brings the payback to a more realistic 35 years. It is questionable whether one would benefit from that level of expenditure, and there may be cheaper and more cost effective means to achieve the same effect.
A Cheaper Option
Over the last few weeks of wintery weather, my day to day gas consumption has been around 110kWh, costing around £3.50 per day. Now suppose that across the heating season, you could achieve a 10% reduction in gas usage through a smarter control system, well that would save about £50 on the annual bill, or possibly up to £100 for some larger users. It could paypack within 2 years.
The average central heating controller is a very simple timeswitch, used in conjunction with an often poorly sited thermostat. It is a technology which has hardly changed for 30 years, and is certainly not best suited to today's lifestyle. With modern microcontrollers and better temperature sensing it should be possible to gain overall better control of the heating system and a higher degree of comfort for lower gas consumption. This was the motivation behind the Navitrino Heating Controller.
The S-Plan wiring schematic for central heating uses two motorised valves connected in series with the room stat and tank stat respectively. When the valves have reached their closed position the circulation pump and boiler are energised.
Many houses have this simple heating plan. The time controller often uses an industry standard backplate, making upgrading the controller relatively simple.
Modelling the System
Firstly it is important to gain a knowledge of the existing heating characteristics of the house. These will depend on type of construction, outside temperature, prevailing wind, and whether intercommunicating doors are left open or closed. For example, one night last week, the boiler stayed on for an unnecessary two and a half hours, solely because the door between the living room and the hall had been left ajar. As my boiler is generally running on average for one hour in every three, that extra 2.5 hours represented a significant extra gas usage. However, for a given outside temperature, a certain amount of heat will be required to maintain the principal rooms at the comfort temperature.
Older houses, without cavity walls need more heat than better insulated ones. You have 2 layers of brick to warm up before the house feels warm, and considerably more heatloss through the solid walls. Older houses were often fitted with open chimneys and sash windows and these too lead to extra draughts and heat losses. For any given house, there will be a certain amount of heat needed to bring it up to temperature, and then another rate of heating to maintain constant temperature determined by the difference between external and internal temperatures. This difference between internal and external temperature may vary widely in cold weather, and it is not unusual for an older house to use twice as much heating fuel on a very cold day compared to a milder day just to maintain a constant room temperature.
The effects of weather can be fairly predictable, for example a cold day in 2010, may follow a very similar temperature pattern to a cold day in 2009, and a knowledge of past temperature profiles could be used to optimise the response of the heating controller to any particular day's weather. The temperature profile of a day could be characterised by just the maximum and minimum temperatures, the average temperature, or a series of readings taken at regular intervals throughout the day and night. The daytime temperature is also reasonably predictable, in that it will generally rise after sunrise and fall after dusk, and the rate of change of temperature lies between certain credible limits in terms of degrees change per hour. Knowing the rate and direction of outside temperature changes would allow a controller to predict where it needs to be in order to maintain comfortable conditions indoors, without burning gas unnecessarily.
A controller could be given a model of a typical winter's day, expressed in likely temperatures, chosen from a short list of typical types. There might only be only a dozen different day models required, to match the temperature profiles of every day between September and April. If these day models are characterised by average temperature, and sorted in order of descending and rising again temperatures, then if you have just experienced a day which matches model type 8, for example, the next day is most likely to be another 8, or a colder 7, or a warmer 9. The controller should be able to anticipate from night time temperatures, taken in the early hours of the morning, say 4am, what the following day is likely to be, and then take the necessary action to ensure that the interior of the house is kept comfortable. If say by 8am, the outside temperature has sufficiently warmed, then the controller may decide that it should be following a warmer profile.
Interfacing to existing systems.
In order to achieve general acceptability, a new heating controller should be easily retro-fitted to an existing system, without the needs for an electrician, plumber or heating engineer - it should be self-installable "Plug & Play" and utilise existing wiring, pumps and valves.
Fortunately, most standard timer based central heating controllers use a common wiring backplate, which allows one controller to be swapped out with a new one or indeed one from a different manufacturer.
This backplate usually has 6 connections, including live and neutral supply connections, and separate outputs for selecting central heating on and hot water on. If heating is demanded because we are in a heating on period, a relay switches live to the heating switched live, and depending on whether the thermostat is closed (demand) this live then energises the heating motorised valve. When this valve has fully opened, a microswitch is activated which then energises the circulation pump and the boiler. Similarly, if hot water is demanded, subject to the position of the tank-stat, the hot water motorised valve is closed and the boiler and pump energised.
So the existing controller could be replaced quite simply with a microcontroller and a couple of mains SPDT relays. Often the central heating programmer is fitted in the most awkward of positions, such as the airing cupboard, where the pump and valves and cylinder are located. This is generally inconvenient and a better solution would be to have a combined programmer and thermostat, which is battery powered and portable and which can be placed within the room where the greatest degree of comfort is needed – such as the living room.
Using wireless technology, this control unit could readily communicate with the boiler control unit to schedule the heating and hot water as required, whilst additionally acting as a display device for showing heating trends, gas usage and offering functions such as hot water and heating boost. This central display would communicate with room temperature and outside temperature sensors, and possibly wireless controlled thermostatic radiator valves, to make a fully integrated zone heating control system.
Some of the work done by Jean-Claude Wippler of JeeLabs on his JeeNode might be of direct relevance such as the JeeLabs RoomNode which was designed with the aim of measuring temperature, humidity, light levels and occupancy via PIR using a simple wireless sensor. Such a sensor network using low cost wireless technology which could be extended at a later date to include other compatible sensors and actuators.
Friday, December 17, 2010
For a Monday afternoon/evening event it was fairly well attended with about 40 to 50 present. Many of these were Homecamp regulars, plus a few new faces.
The evening consisted of several interesting presentations on energy, cleantech and interconnectivity, with plenty of beer, wine and pizza which gave the event an informal, social atmosphere.
After James Governor's excellent opening address, first up was Gavin Stark founder of AMEE who described how AMEE were now codifying nearly a million different variables around the world.
Andy Piper, of IBM, Hursley, spoke about MQTT as a means of achieving interconnectivity between physical computing devices, and quoted some examples developed by Andy Stanford Clark, who unfortunately could not attend.
Usman Haque and Ben Pirt of Pachube presented an update on the new features included in the recently released new Pachube API.
Georgina Voss of Tinker London described the first phase Homesense Project - making Arduino technology available to real families and households with the intention of incubating new projects in home energy efficiency and lifestyle change.
Unfortunately, the 8pm deadline for closure of the venue came around all too quickly, and so we quickly re-charged on pizza and retired to the local Queen's Head pub. Regrettably there was not enough time to hear all of the presentations and get around to talking to all the attendees, hopefully Homecamp4 will be a full day event, and less pressurised for time.
Thanks must go to Mike Beardmore @mikethebee and his wife, who organised the venue and were perfect hosts. Additionally to James Governor's firms Redmonk/Greenmonk who sponsored the pizza and drinks.
All in all it was an excellent evening, and just what was needed during these dark days in the run up to Christmas. Hopefully it will have sustained the momentum of the Homecamp movement and given attendees something to think about over the Christmas break.
One of the people I did get to chat to was Simon Daniels, CEO of Moixa Technology
Simon described his low voltage dc household power distribution system. The concept is based on the premise that more and more of our household energy consumption is low voltage dc needed for an ever increasing variety of low wattage electronic devices which fundamentally run on dc, such as consumer electronics and LED lighting. Low voltage dc can efficiently be distributed on a household scale using existing wiring, with surprisingly low cable losses. This eliminates the needs for lossy ac to dc adaptors, and produces a power system which is efficient and compatible with home scale renewable energy devices.
Simon describes how a small window sill mounted pV solar panel, could be installed to many properties, such as flats, where access to the roof is not available, and at a price of £1K to 3k making it more affordable than a full rooftop solar installation. The dc from the solar panel would recharge a lithium battery system and provide sufficient power for the dc distribution system. A small solar panel of perhaps 200W could provide sufficient power to offset between 5% and 15% of the domestic bill.
For this technology to gain momentum, the large manufacturers of electronic goods and appliances need to collaborate on standards for dc supply, cabling and standby switching. A generic dc cable, for example based on a USB cable but with an additional pair of high current contacts to supply the variable voltage dc power. A process similar to USB enumeration would allow the device or appliance to be recognised by a central power controller, and supplied with the correct voltage. The standby modes of many devices, such as microwave ovens, are particularly inefficient, as they need to use 50Hz transformers to provide small amounts of dc power to run the timer or clock functions. By adopting a hybrid system of a dc cable for standby mode and control and a conventional ac connection for high wattage loads, would minimise the standby load to a few tens of mW plus offer the possibility of dynamic demand control. A washing machine with a timed standby mode could be automatically scheduled to run during a time of low grid usage, or the washing heating cycle paused and restarted, on the event of a sudden large demand on the grid.
Moixa will be running field trials in the Spring.
The Moixa technology is an example of a range of disruptive technologies which will ultimately change the way in which we use and pay for energy. Industry analysts have coined the term "Electricity 2.0" to describe the outcome of these changes. When combined with other systems such as smart metering, demand based tarrifing and dynamic demand control of appliances, the package could add up to significant energy savings within the household. Every kWh of electricity saved in the home is 2kWh off the nation's gas bill and more importantly less CO2 and waste heat into the atmosphere.
By introducing an energy storage element into the grid, possibly in the form of wide scale roll-out of Moixa's dc battery system, will allow consumption to be time-shifted out of peak time, and greatly assist in load balancing. Improved load balancing will permit the wider use of intermittent generation technologies such as solar and windpower, plus reducing the wasteful start-stop cycling of conventional generation plant.
With the recent and persistent cold weather, the annual subject of home heating and fuel efficiency has once again come to mind. In the next post I will describe some recent musings.