Category Archives: Gas

The Big Picture

After a series of quite detailed posts, I think that the time has come for an updated high level overview of what we have.

Heat loss from the home

We moved to our early 1970s house almost 4 years ago bringing with us our electric vehicle. The house had already been refurbished with new double-glazed windows, had cavity insulation (although that wasn’t recorded on EPC so must have predated the prior owners), and a token level of loft insulation. The existing gas boiler was arthritic, couldn’t heat the whole house, but was quite good at heating the header tanks in the loft! We had gravity-fed gas hot water (i.e. no thermostat or pump on the cylinder) which was completely obsolete, the cylinder dated back to the building of the house and had no immersion heater (although we had the wiring for one). So what did we do?

Space heating:

Eve Thermo eTRV
  • We substantially increased the loft insulation to reduce heat loss.
  • We had a modern condensing gas boiler installed to improve efficiency.
  • We updated to smart controls using eTRVs to set both temperature set points and schedules at room level. I built a smart interface to the boiler so that heating can be enabled remotely. I programmed a series of rules into Apple Home allowing the smart thermostats to enable the boiler when any thermostat wants heat and disable it when no thermostat wants heat. Some rooms also have additional rules linking heating to open windows or movement sensors. All of this reduces heat losses by only heating rooms that are (or will be shortly be) in use.

Electricity supply:

Solar panels
  • We installed our own solar panels given 4 kWp generation. (I also own a small share of a solar farm although there’s no contract that I’m aware of between that farm and my home energy supplier)
  • I invested in an immerSUN to maximise self-use of our own solar by enabling loads when surplus solar is available.
  • We switched to a green electricity supplier so when we need to buy electricity it comes from renewable sources.
  • We bought a small storage battery 4 kWh to store some of our solar production for use later in the day. Subsequently I can also use it in winter to buy when the electricity price is relatively low to avoid buying when the price is relatively high.
  • We chose a dynamic smart tariff to buy electricity at the lowest price based on market prices established the day before. The prices change each half hour and are established in the late afternoon on the day before.

Water heating:

Hot water cylinder
  • We replaced the old hot water cylinder with a modern insulated one (to reduce heat loss) with a low immersion heater (to allow more of the water volume to be heated).
  • Our principal water heating is now by diverting surplus solar electricity proportionately to the immersion heater, that’s backed up by the gas boiler which is enabled briefly in the evening for water heating in case the water isn’t yet up to temperature, and when the electricity price falls below the gas price I can enable the immersion heater on full power.
  • All accessible hot water pipes are insulated.

Electric car charger:

Electric car charger.
  • I built my own electric car charger that takes an external radio signal to switch between four settings 0, 6, 10 and 16 Amps to help me adjust consumption to match to availability of output from my solar panels. (Subsequently such products were developed commercially with continuously variable current limits, but the limitations of my immersun and on/off radio signal don’t allow me to go quite that far. Having said that my car only does 0, 6, 10 and 14 Amps so I would gain no benefit from a continuously-variable charger paired with a 4-level car).

Smart electricity controls:

Smart controls
top: HEMS (to manage bought electricity) and junction box
mid: radio transmitter (to car charger)
bottom: immersun (to manage self-consumption)
  • We have two systems for smart control of electricity:
    1. The immersun to maximise self-use of our solar electricity by proportional control of loads.
    2. A HEMS to manage the purchase of electricity (when necessary) at the lowest price by maximising consumption when the price is lowest.
  • When both systems want to enable loads (because the bought price is low and we have a surplus from our own panels) then cost is prioritised, so we’ll buy from the grid any demand not being met from our own panels.
  • Both systems are linked to 3 devices:
    1. Battery storage. The immersun is configured to work alongside the battery storage with the battery storage as the top priority to receive surplus solar PV. The HEMS can switch the status of the battery as required to charge from the grid when the price is lowest, or to discharge when the price is highest, or indeed to revert to default behaviour.
    2. Car charger. Second priority for the immersun after battery storage.
    3. Immersion heater. Third priority for the immersun after car charging.

The future

I have no firm plans for the future. I’m toying with adding to the HEMS various features including:

  • Making the display switch between GMS and BST as appropriate (it’s all UTC at the moment).
  • Edit configuration via the web interface rather than a virtual terminal.
  • Control a domestic appliance. Our washing machine was replaced relatively recently, but the dishwasher is playing up a little and may be a candiadte for HEMS integration where the optimum start time is selected to deliver lowest energy price.

Gas Usage to July 2018

This chart shows our gas consumption by month and year since we moved here in August 2015 (the first full month shown is September 2015),  Along the way several changes are marked which might be thought to influence gas consumption, although with natural variation month-to-month and year-by-year the effect of those changes isn’t dramatically obvious.

What is of course obvious is the dramatic difference in gas consumption between summer and winter as gas is our main means of space heating, and there’s no need for space heating in summer.  Most homes would exhibit such a pattern.  Ours is probably a bit more marked than many because of our water heating.  Many homes with gas will use the gas for both space and water heating, but for us the gas water heating is the back-up not the primary water heating system.  Our home is set up to divert surplus solar electricity from the PV panels to water heating during the day.  Only in the evening is gas water heating enabled and then it does no heating if the water is up to temperature.  The gas water heating thermostat is also set a few degrees colder than the immersion heater, so gas is separated from electric water heating by both time and temperature to prioritise electricity.

Previously I had just disabled the boiler in summer, but occasional dull days would leave my wife complaining about lack of hot water.  The new arrangement with the boiler operating later and with a lower temperature set-point has avoided that and is robust as long as your hot water cylinder is big enough for your daily needs so you only need to fill it once with hot water which is then stored available for use until the next day.

Over time 3 changes are called out which should reduce gas consumption further:

  1. In December 2015 we replaced the boiler, hot water cylinder and controls.  The previous boiler had demonstrated that it was incapable of heating the whole home as we went into our first winter so a replacement was rapidly arranged.  The new boiler is considerably more efficient which should reduce gas consumption for a given heat output, but it now heats the whole house, so that might counteract the improved efficiency.
  2. In late 2016 we upgraded the loft insulation from 100 to 270 mm which should be worth £73 in gas per year according to our EPC.  February, March and April 2017 do seem to show some benefit compared to 2016, but then there also variation in the weather year-to-year.
  3. In May 2017 we started adding smart heating controls which has gradually expanded over the following months.  The overall concept here is that most rooms now have smart radiator valves which are both thermostatic and contain their own schedule.  The schedules allow rooms to be heated for fewer hours: for example lounge not heated on weekday mornings, playroom not heated after children’s bedtime etc.

Advantages of smart heating

I thought that I’d describe some of the features of the smart heating controls versus the prior single zone system with TRVs and a 7 day timer. My main interest is of course to save gas by heating the home more selectively, but there are other opportunities that you may consider significant.

I don’t yet have sufficient data to illustrate any operational savings, but continue to record gas consumption to compare with prior years.

 

 Prior system with 7 day timer and TRVsCurrent smart system with some eTRVs
ZonesSingleMultiple
Schedule7 day - working week plus weekendsInfinitely flexible home / working schedule based on iPad calendar
Adjustment of timers and thermostatsManualvia App (with voice control!)
Remote adjustmentNoYes - enabled by Apple TV as hub
Holiday settingNo Yes - sets low level heat for frost protection
Summer settingNo Yes - closes all valves
Integration with non-heating smart devicesNoYes

Internet of Things

Last night I made a small update to our heating system by adding some smart radiator valves. I’d been thinking for some time that there were efficiencies to be made regarding what rooms were heated when. Until now we’ve had a 7 day heating timer (so we have different heating schedules on weekdays and weekends) and thermostatic radiator valves (so we can set specific temperatures in each room) but now we’ve gone a step further.

Radiator valve

Radiator valve

These days there are in my opinion three types of radiator valves:

  1. Traditional proportional valves – these valves allow the flow to a radiator to be set manually, but there’s no control to maintain a set temperature. So if for example a room is south-facing it may get too hot on a sunny day as no account is made of the solar gain, or a relatively exposed room may get too cold on a windy day as no account is made for the extra heat loss.
  2. Thermostatic valves – here the user can set a temperature for each valve, and then internal expansion or contraction of the thermostat reduces or increases the flow through the radiator to maintain the set temperature; but all radiators heat at the same times as set by the heating timer.
  3. Smart valves – smart valves add the ability to schedule temperature and/or on and off periods in different rooms at different times.

Valve Schedule

In my case I identified 3 rooms (5 radiators total) in which I thought that the typical usage was different enough from the house as a whole to warrant smart valves. For the purposes of illustration only, I’ve also added the schedule for the boiler timer although this is programmed independently of the radiator valves. The three rooms are:

  1. Lounge – we don’t use the lounge on termtime weekday mornings.
  2. Master bedroom – we don’t use the room during the day, so the heating can stay off until towards bedtime.
  3. Play room – my daughter doesn’t use her playroom before nursery or after her bedtime.

The chosen smart valves are Elgato Eve Thermos which are Apple HomeKit compatible but are also configurable via Elgato’s own App; but not configurable via non-Apple devices. I initially tried setting up the required sequences via timed scene changes, but couldn’t see an easy way to schedule both workdays and days off; so I ended up downloading schedules directly into the valves via Elgato’s own App. This allows different schedules to be established easily for both working and non-working days with a schedule to identify non-working days set in as a calendar in my iPad. It’s easy to set up a recurring schedule for weekends and then other dates like bank or school holidays can quickly be added. Vacations when we’re away from home are still set up via timed scene changes.

Discounted renewable power

img_0596We’ve recently moved to Bulb as our electricity and gas supplier. Bulb is a new company founded by Hayden and Amit providing 100% renewable electricity and 10% renewable gas and, for us, was the cheapest provider of the same.

Bill logo

Bulb logo

Bulb are currently offering a £50 discount to new customers via this link, so there’s even more incentive to go renewable.

They also have 9.8 out of 10 on TrustPilot, a UK call centre, and are a Living Wage employer.

Making best use of energy

If I want to make best use of my solar PV (i.e. use as much of it as possible) then it seems logical to prioritise replacing my most expensive energy purchases. Examination of my bills suggests that my different sources of energy have the following costs:

  1. Day-time electricity: 12.31 p/kWh
  2. Night-time electricity: 8.02 p/kWh
  3. Any-time gas: 2.87 p/kWh
  4. Solar PV (when available): 0.00 p/kWh

In winter when little PV electric is available our normal practice is to shift as much electric load as possible to night time use saving 4.29 p/kWh by use of timers. Washing machine, dishwasher, and electric car charging all get shifted to Economy 7 by use of timers. The washing machine is the oldest and uses a external timer plug while both dishwasher and car have their own inbuilt timers allowing consumption to be delayed.

In summer the same approach can be used to shift these loads to daytime to make use of solar PV although if the weather is dull and cloudy there’s no guarantee that sufficient PV will be available risking consumption of bought daytime electricity.

My Immersun already minimises exported/surplus PV by running the immersion heater to mop up surplus electricity, although as gas is cheap the savings are smaller than might be achieved by avoiding a similar amount of night-time electricity consumption. In winter we minimise gas use for water heating, while still providing a gas safety net by displacing in both time and temperature. The Immersun naturally heats water in daylight hours only and generates hot water at 60C (not adjustable) as defined by the immersion heater thermostat. The gas is set to complement this being set by timer not to overlap Immersun hours and is set to 50C by the cylinder thermostat. The water temperature difference is not noticeable in practice especially as the showers are thermostatically regulated.

Car charging 1The device that consumes most electric power is undoubtedly my electric car. Its usable battery capacity is about 10.5 kWh and, with charging efficiencies, it can take up to 12 kW of mains electricity to charge (less in summer). The appeal of charging this on solar PV is high, although the cost of doing this if it inadvertently draws day-time electricity is also high (but still much cheaper than petrol or Diesel). It occurred to me that it would be good to use spare channels on the Immersun to control car charging as my largest consumer of my most expensive fuel. It has three channels – two variable power and one on/off – although it can be configured to produce three variable outputs using the on/off to switch between devices.

It seems to me that there are three alternatives for control:

  1. Proportional control.
  2. Stepped control.
  3. On/Off control.

Proportional control would be the most capable. The Immersun has the capability to provide proportional control to multiple resistive loads, and the Mode 3 communications standard to which virtually all electric cars adhere also provides for the charging equipment sending a proportional signal to the car via PWM, so there’s scope for a proportional system. However it seemed that the time to develop this was beyond what I have available, and in practice although the car would receive a proportional control signal it would normally respond in a stepped manner so there’s little to be gained by investing my time to develop a fully proportionate system..

Stepped control is easier to achieve. As it happens my car model is more steppy than some as I believe that it switches between 6, 10 or 15 Amps consumption only. 15 Amps is very close to the full 4 kW output of my panels and, given that there are always other loads in the house, then I don’t think it would ever use this setting, which leaves me with switching between 0, 6 and 10 Amps. Unfortunately of course you can’t switch between 3 states with an on/off signal that only has 2 states, so I’d still need to decode an analogue Immersun output or invest in a second Immersun to get another on/off output but I deemed the latter cost-prohibitive. Generating a variable current signal to the vehicle would also require some logic to reduce the pulse width on the PWM signal on demand – not impossible but still requiring some time to create.

That leaves me with on/off control at a fixed current. This is readily achieved from the Immersun which has a relay output that can be configured to operate when a certain solar power is available (such as 1.5 kW to drive a 6 Amp charger). I decided not simply to turn the whole charger on or off by switching the power as this would cause the mains contactors in the charger and the HV DC contactors in the vehicle to drop out under load which is bad for longevity. Instead I’ll interrupt a low voltage control signal within the charger to trigger stop and restart in a more controlled manner – effectively car and charging equipment will see the signal as the user wishing to disconnect the cable as you might if you wished to drive before charging was complete.

Finally I considered how to connect the Immersun to the charging equipment. Unfortunately the Immersun is in the airing cupboard upstairs (where it drivers the immersion heater) and the garage where the car charges is a separate building alongside the opposite side of house. Neither a second Immersun or a physical cable looked like an attractive prospect on cost grounds so I decided on radio control using around £20 of home automation parts and a total investment of around £40. More on this solution over the next few weeks.

End of 2012 Gas Analysis

Well like many UK homes our central heating and hot water is fuelled by natural gas. We also use natural gas for cooking on the stove top (the oven is however electric) and we have a gas fire in the living room, but these latter two uses are much less significant.
I’d lived here for 10 years before I started actively trying to reduce my energy consumption. During those 10 years I used an average of 562 units of gas annually.
Since then I’ve reduced my consumption by two routes, firstly to reduce heat loss so that less energy for heating was required, and secondly by replacing gas with renewable sources. It’s however also the case that my circumstances have not been constant during that time so, for example, when I started this I lived alone then 4 years or so ago I married and my wife joined me here; and now my wife is at home during the day with our baby daughter much of the time. Consequently the demand for hot water for washing and heating has increased.
The steps taken to reduce gas consumption include:

  • Having insulation installed in the cavities of the house walls. Houses here conventionally have a double skin of brick or block and, when this house was built, the cavity between the inner and outer layers was usually left as an air gap. We’ve had that gap filled with insulation as you would find in newer homes.
  • Increasing the thickness of insulation in the loft.
  • Replacing the old wooden windows with new PVC ones with higher “A” grade insulation – most easily seen by the larger air gap in the sealed units.
  • Installing solar water heating panels on the roof in conjunction with a larger hot water tank. In the summer these provide almost all our hot water (no heating is required), although at olther times of the heat they don’t provide enough heat alone for hot water they can help to pre-heat the cold water leaving the gas less work to do to achieve a usuable temperature.

We didn’t do this all at once, but if I compare the last 2 years to the original 10 year baseline then we’ve reduced average annual gas consumption by 23%. I think that the reduction would have been higher had our circumstances between constant.