Saturday, October 23, 2010

Heating Older Houses

As some will be aware I am in the process of monitoring my domestic heating system, with the intention of developing a heating controller that offers better performance than the existing timer/thermostat one that is fitted.

The Navitrino has now been running for a few days, logging the outside temperature, the living room temperature and controlling the boiler so as to keep the living room temperature between comfortable limits.

The graphs show the variation in inside and outside temperatures over 31st October and 1st of November. On the 31st we had the woodstove blazing - not a very controllable heatsource - thus the peak of 24C and the slow cooling back down to 18C over a period of 16 hours. During this time outside temperatures were fairly mild - between 6 and 12C.

I believe that the thermal demands are unique to each property, which coupled with widely different lifestyles and levels of occupancy mean that there is no "one size fits all" solution to domestic heating control.

I have already written some control software, to control the heating, and found it convenient to split the day up into 3 time periods - loosely called Day, Evening and Night corresponding to periods of occupation and activity. For example in the evening when the living room is normally occupied, 20C is a comfortable temperature, whilst during the day 19C may be more appropriate. At night time, when the livingroom is unoccupied it may be acceptable to relax the temperature requirement to 17C, which allows more economical use of gas, but allows for a relatively quick warm-up.

The first stage is to monitor the thermal profile of the house, and the boiler behaviour and gas usage, for different external temperatures and generate a simple model of the thermal behaviour of the property.

My house has solid 9" walls and 4" internal brick walls. The living room has a large chimney breast which also retains a fair amount of heat.

What I hope to establish is a series of warm-up times, based on a given starting room temperature and setpoint versus the outside temperature.

Once the thermal mass of the room has been warmed up, the house will take much less heating power to keep it at the comfortable temperature.

For example, yesterday lunchtime between 12 and 1pm, it took 27kWh of gas to raise the room temperature from 17C to 20C. Once warmed up, the 20C room temperature could be maintained for the rest of the day and overnight with just 3kW heat (57kWh energy). During this time, the outside temperature varied between 12C and 9C - so not particularly cold.

The intention is to repeat these measurements for a range of outside temperatures. What is likely is that the 1 hour/ 27kWh "boost" heat will become longer in duration and use more kWh as the outside temperature falls.

I should mention that the heating system at the moment consists of 3 room radiators - with TRV, a bathroom towel radiator and 25m2 of underfloor heating. This heats the living room, kitchen, bathrom, my work room and 1 bedroom on TRV set to low. These rooms we consider to be the core of the house, leaving hall, and unused spare bedroom not directly heated.

Friday, October 22, 2010

Gas Meters Revisited!

In the last couple of days I have run a multicore cable from my work room at the back of the house to the gas meter which is under the stairs.

After two days of frustration caused by noisy optical sensors and false triggering, I decided to use one of my newly acquired Hall effect sensors as used on the Lister spark ignition circuit.

I have used a Hall effect sensor Farnell 178-4735 )

clipped exactly in the same place as the optoreflective switch.

The Hall sensor is mounted so that the face with writing on it, which is triggered by a passing North pole is pointing towards the least significant digit wheel.

This wheel contains the magnet, roughly in the same position as the silver reflective zero digit.

The hall sensor will work from 3V or 5V systems and needs a 10K pull-up resistor because it is open-collector.

As the magnet passes, the open collector output goes cleanly to 0V. Many of my problems with the optical sensor was due to signal bounce and noise pick-up. This inexpensive Hall sensor seems to have cured all that.

To connect up you will need a 3 way cable, or if running a long distance - something like screened microphone cable would be suitable.

I'm still testing to make sure that my pulse bounce and false counting problems have gone away - it's interrupt code on the Arduino, so needs careful debugging to make sure its working correctly.

This gas logging ( and central heating control and monitoring) is all part of the work that I am doing on the Open source Navitrino project.

Sunday, October 17, 2010

Navitrino Progress

Navitrino is a modular open source project intended for monitoring and controlling domestic energy usage.

Navitrino is an experimental platform, compatible with low cost Arduino hardware, which can be customised to meet the requirements of the individual's home energy installation. Navitrino can be assembled from off the shelf Arduino hardware, and programmed readily using the Arduino IDE.

Today's domestic energy systems are becoming more sophisticated with the addition of solar water heating, solar pV, heat-pumps and the like. Navitrino has been designed to monitor the key parameters of the system, make decisions based on usage, lifestyle and climate conditions and intelligently co-ordinate the various energy sources.

Navitrino was conceived with the following uses in mind:

1. Solar Water Heating Controller - simple control with circulation pump relay
2. Central Heating / woodburner controller - determines best usage of hot water
3. Electricity Monitor - whole house electricity consumption
4. Gas consumption monitor - pulse counter on optical or magnetic sensor on gas meter
5. Battery management system pV / battery charge controller/datalogger for wind or solar pV
6. Gasifier controller
7. CHP controller - engine start/stop, rpm, voltage monitor etc
8. General purpose control tasks
9. Temperature, climate and weather monitoring and datalogging
10. General purpose energy monitor for performing home energy surveys

Navitrino as a concept was intended to be as flexible as possible, so if a new bit of equipment or technique comes available, Navitrino can be extended and updated to cater for the upgraded system.

Navitrino is based on a nework of interconnected nodes. Whilst one device might be controlling solar and domestic water heating, another device may be used to monitor and log the household electricity and gas usage. Devices can share data with one another using a simple serial data format which is compatible with both wired and wireless networks.

Navitrino uses low cost, off the shelf, open source Arduino hardware as the basis of the project.
The Freeduino and accompanying sensor shield from NuElectronics, which has real time clock and SDcard interface provides the hardware.

Alternatively, if the final intention is to incorporate a Zigbee wireless network the "Stalker" board from Seeeduino Labs in Hong Kong also makes a ready to run platform.

Central Heating Controller.

During the summer months I have been slowly getting together all the necessary elements of the Navitrino project; sourcing the hardware, building up the sensors and writing some rudimentary code routines to exercise the hardware.

As we have now officially entered the UK heating season, one of the first projects for Navitrino is to monitor and control my central heating system.

I have mentioned this in an earlier post about using a DIY controller to monitor and control the home central heating system. Now is the time to put these ideas into action.

The task is fairly simple, the controller will monitor the living room temperature using a thermistor temperature sensor, and turn the central heating boiler on and off in order to maintain the living room temperature at a level as set by a rotary potentiometer.

In addition to the room temerature probe and the set-point control, the Navitrino also monitors outside temperature, the hot water tank temperature (2 places) and a light sensor placed in the living room. The idea of the light sensor is that it can be used to determine the living room occupancy - when the lights are switched off at bedtime, the heating will either shut down or revert to a lower temperature setting.

The controller also incorporates an interrupt driven pulse counter, which allows it to count pulse data from a gas or electricity meter - so that home energy consumption can be monitored. I am particularly interested in gas consumption and being able to relate it to central heating usage and outside temperatures.

Over the last few days, the prototype Navitrino has been controlling the central heating, datalogging temperatures and counting pulses from the gas meter.

Originally, I used an opto reflective sensor to detect the "silvered zero" passing by on the least significant digit wheel of the gas meter index. Whilst this initially showed promise, I found that the rising and falling edges of the pulses were prone to "bounce" which caused false triggering of the pulse counter. I have subsequently replaced the opto-sensor with a Hall Effect magnetic sensor - because the same reflective zero also contains a small magnet, intended to trigger Hall sensors or reed relays.

Wednesday, October 06, 2010

Arduinoids - The Rise of the Machines

Back in July I was contacted by Nikki of fizzPop Hackspace in Birmingham about making very low cost Arduino clones on stripboard. I hadn't really given it much thought until I realised how easy it would be to make an Arduino compatible device on stripboard (or breadboard) for something less than a fiver!

I've tried to standardise the design, to make use of the ATmega328 pin-out - which lends itself for an efficient layout.
Here's a couple of recent boards - one is a controller for a spark ignition system, and the other is a general purpose layout - just the Arduino in the corner of a vast expanse of prototyping board.

Below is the prototype spark ignition controller. It is based on the Atmel ATmega328 microcontroller and uses the standard FTDI USB to serial cable as a means of programming it.

The schematic is here: Lister_spark_IC.pdf

The following I/O pins were used

Pin 2 Serial Rx Input from PC

Pin 3 Serial Tx Output to PC

Pin 4 Digital Input from Hall Effect sensor (Arduino Digital Input 2)

Pin 14 Digital Output to trigger power transistor (Arduino Digital Output 8).

Pin 19 Digital OUtput to Drive LED (Arduino Digital Output 13).

The board is clocked with a 16MHz crystal to retain compatability with Arduino. The firmware is developed as normal using the Arduino IDE.

The board has a 5V regulator, a rotary pot to delay the spark and a blue LED to flash in time with the firing of the power transistor. The TIP122 transistor is mounted on a small heatsink. Connections to +12V battery, ground and the low tension to the ignition coil are provided on 1/4" automotive spade terminals. The 6 way cable exiting to the top left is an FTDI USB to serial cable. This provides +5V for testing and the serial interface for programming the board and getting rpm and ignition delay data back to the laptop.

The 3 pin Hall sensor plugs into the pin-socket just below the FTDI cable header - it has the same pin order as the Honeywell sensor +5V, 0V and signal out. For testing the sensor device can be plugged straight into this connector, and later extended with a 3 way cable.

The board measures 3" x 4.5" and there is space below the heatsink to take additional circuitry. You will need bit of stripboard at least 28 holes by 32 tracks to copy this layout.

Only 4 of the I/O pins are being used in this application, leaving the remainder for other future use.

One possibility is to add a further pair of TIP122 transistors, so that this board could form the basis of the spark controller for the 3 cylinder Kubota engine. If additional TIP122 transistors are added, they need to be isolated from each other if used on a common heatsink.

From the top the spade connectors are +12V, battery ground and coil output.

As a general point, the pin-out of the Arduino (see below) and ATmega328 maps very easily onto breadboard or stripboard. This means that small Arduino compatible projects like this can be made on stripboard or even breadboard at a fraction of the cost of buying the real Arduino and building a board onto it.

Buildtime was approximately 5 hours - but that included a lot of thinking time to get the component positioning sensible. To copy this board would take a couple of hours.

The second board is built along similar lines. At first it's just a microcontroller in the top corner of the board.

Here's the Partslist for the simple Arduino clone

1 ATmega328 microcontroller
1 28 0.3" pin DIL socket
1 7805 5V voltage regulator
1 16MHz HC49-4 crystal
2 10K resistors
2 330R resistors
1 1K resistor
2 22pF ceramic capacitors
4 100nF ceramic capacitors
2 22uF 16V electrolytc capacitors
1 1N4001 diode
1 LED - to show that life exists!
1 Stripboard at least 28 holes x 20 strips
1 6 pin 0.1" header
1 optional reset switch
Additional 5 and 6 pin 0.1" SIL sockets for connecting external I/O
single core hook-up wire - 4 colours used

1 FTDI cable for programming (optional) (ATmega328 can be programmed on Arduino board and swapped across).

The following additional parts were used on the spark ignition controller project.

1 10K rotary pot or trimmer pot
1 Hall sensor (Honeywell SS441R)
1 neodymium disc magnet
1 M3 (or equiv) bolt and nut for fixing heatsink
1 3 pin 0.1" socket
3 0.25" pcb spade connectors
1 TIP122 darlington power transistor
1 Heatsink