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Green dining

RG323843 — Mon, 06 Sep 2021 11:49:22 GMT

THE DEVELOPMENT OF A STORAGE COOKER THAT COULD BECOME THE HEART OF YOUR HOME

The storage cooker is inching closer to the final product - the image above is of Version 03 in the workshop. This will ultimately be a demonstration model that will be installed in to a family home for further testing and monitoring and we plan to share every stage of this process in this blog. The thermal store is up and running without insulation and the temperature of all surfaces is being measured to determine how the stored energy is being distributed.

The image above is of the first two layers of high temperature fire bricks of Version 03, supported on three layers of 50mm thick high temperature ceramic insulating boards. There will be a stainless steel plate used to hold the bricks in place, to conduct heat to a Plate Heat Exchange (PX) unit and to provide fixings for the Pyrogel insulation. You can see a tiny green cable running from underneath the unit - this is connected to a thermocouple on the floor under the unit to measure the temperature of the floor throughout trials.

How does the cooking happen?

The diagrams above show the next stage of the project - attaching the stainless steel plate (on the left) and then attaching the Plate Heat Exchange units (as seen on the right). Two Plate Heat Exchange units will transfer the heat from the brick core to air that is used to a) heat the main ovens, like a fan oven, or b) heat air that will be used for heating space in the house. These boxes will have three openings side by side at the bottom of the box - one at the back, one in the middle and one at the front. Because the openings are at the bottom, there won't be any natural convection currents (hot air rising) driving the air in and out. This means that there won't be any uncontrolled air movement and thus, any uncontrolled heat transfer or heat loss.

We will be using a fan from a fan oven to draw air out of the middle opening when heat is needed in the oven. The plates inside the box result in the very hot air at the top of the box being drawn out first (giving instant heat) and the coolest air at the bottom of the oven being drawn into the openings at the back and front to replace the air that has been drawn out. The fan will be speed controlled which will give very precise instant control over the rate of heat transfer and this the temperature in the oven. There will be two of these units - one at the bottom of the unit (as shown above) and another at the top. The top unit will be for the hot oven and the bottom for a cool oven or heating space - a little like the different ovens in a traditional range cooker. There will also be one or two hot plates on top of the unit for frying/boiling.

The above image shows the cooker with the two Plate Heat Exchange units (one on top of the other) for the two ovens and the rough dimensions of the overall unit. The below image describes the flow of air and heat

Carrigbeg

Thu, 27 Aug 2020 10:18:52 GMT

Family home in Dun Laoghaire

Carrigbeg is a detached house in Dun Laoghaire built in 2009 with eight 160Wp Solarfun Monocrystalline PV modules on a south facing roof with a slope of c.35°. The DC output from the PV modules is converted into AC electricity by a Fronius IG15 inverter. The AC supply from the inverter is connected to the main household AC circuit. A MyEnergi Eddi controller diverts surplus PV output to a 3kW immersion heater in the HW tank. The house, which is occupied by two adults, is heated by a condensing gas boiler. Monthly energy consumption in Carrigbeg has been recorded since the Eddi controller was installed in February 2019. The resulting data set is summarised below;

Comparisons

A comparison between the two sites in Dun Laoghaire (Carrigbeg and Cherrytree Lodge ) are interesting. The seasonal differences are the result of slightly different locations and orientations.

The Green Building

RG323843 — Thu, 14 May 2020 10:15:05 GMT

Urban sustainablity

The Green Building in Temple Bar was built in 1994 and illustrates how environmentally friendly buildings can help to achieve sustainable urban areas. It includes 8 carefully designed apartments, a ground floor retail space and a basement office floor. The building was designed to minimise undesirable heat gains and losses and to maximise the use of solar energy both directly in the form of heat and light and indirectly by using sun, wind, bedrock energy and stack and canyon effects. Intake of cold air during the heating season is minimised by the use of foliant species to recondition internal air. Cooling is aided by the suppression of core temperatures at night both by enhanced upward radiant losses and "canyon" convection effects. Roof mounted wind turbines and PV panels provide electricity for lighting. Evacuated tube solar collectors provide energy for hot water systems and a heat pump is used to heat the building in winter by extracting low grade energy from the underlying bedrock.

In 1995, the Green Building won the RIAI regional award for Dublin and it also became the first ever EN50438 (Irish settings) compliant grid connected PV system in June 2006.

The Green Building has an A energy rating, contributing to the ESB grid. Since completion the project has been extensively published in Ireland and Europe and has come to be regarded as a key development in the evolution of sustainable building design.

Green Building in Temple Bar is showing alarming heating of bedrock under Dublin

The temperature of the limestone bedrock deep under Dublin has risen dramatically since the borehole for the Green Building in Temple Bar was first tested 28 years ago.

The temperature of this bedrock is checked from time to time by Tim Cooper as part of his on-going monitoring of the performance of the building. The most recent readings, taken on 13 August 2021, showed that the temperature of the bedrock has risen by 2.5°C in the last 28 years .

(These temperature readings were taken using the same two temperature sensors on 9 September 1993 and 13 August 2021. Both sensors gave readings that were within 0.1°C of each other (see readings below), so there is no reason to suspect that they are inaccurate).

Borehole flow and return temperatures

This astonishing data suggests that the entire planet, not just the atmosphere, is heating up dramatically. The only cause for this heating that we can think of is global warming, which was flagged dramatically in the slides presented by Tim Cooper at the launch of the Green Building on 14th September 1994 – see below.

Slides from lecture given by Tim Cooper in 1994

Cove Mews

RG323843 — Thu, 14 May 2020 10:12:02 GMT

Optimising use of PV output in 120 m2 house, built to Passive House Plus standard.

The Passive House Plus standard when applied to this house indicated that the capacity of the PV array must be c.8.16 kWp at minimum. This was achieved using 24 LG 340Wp solar PV panels oriented East-West at a slope of 10°. The annual output from these PV panels, calculated using PVGIS, is 6,612 kWh.

The total energy demand of the house (which is largely used for hot water and non-space heating appliances), calculated using 5-minute operating schedules for all electrical equipment and appliances, is 6,907 kWh.

The above figures indicate that total PV output is similar to the household demand, assuming that the PV output profile matches the household load profile but in reality these profiles are very different indeed – see below.

These snapshots show the mismatch between PV output and household demand in June and December. The figures for other months fall between these extremes. Summed over the whole year, the surplus PV output amounts to c.4,550 kWh (65% of total output) and the shortfall amounts to c.4,485 kWh (65% of total demand). Without correction all of the surplus would be exported and all of the shortfall would be imported. The options for correcting this were;

1. Hot water storage system (HWSS)

2. Battery energy storage system (BESS)

3. BESS plus HWSS

4. An electric vehicle (EV)

Our analysis of these options is summarised below.

The approach we took was to provide a reliable method for evaluating the options for optimising the use of surplus PV output. This enabled the owner/designer to select a combination of technologies best suited to his particular needs/aspirations. In the course of this it became clear that there isn’t a single fit-for-all solution - it’s more a case of horses for courses.

Cherrytree Lodge

Mon, 06 Apr 2020 10:42:33 GMT

Cherrytree Lodge is a 184 m2, A3 rated house, which was completed in February 2015. It is fitted with a whole house heat recovery ventilation unit. Heating and hot water is produced with a condensing gas boiler and a 4 panel 1 kWp PV system with string inverter. There is slight winter shading (that is increasing because of distant tree growth). The house is occupied by two adults and two children.

Our original brief was to comply with building regulations in the most economical way possible. The conclusion was that the condensing gas boiler, whole house heat recovery ventilation plus a 1kWp solar PV array was the lowest initial cost solution. A DEAP assessment showed that this met all the required target - annual energy consumption, annual CO2 emission and percentage renewable energy. Annual energy costs weren't a major consideration and, in any event, were very difficult to determine because of the mismatch between solar PV output and household demand – see figure 1.

Because of this mismatch, a considerable amount of the electricity generated by the solar PV system would be exported every year if nothing was done to prevent this. With this in mind, a diverter was installed in October 2018. This diverts all the surplus PV output to the immersion heater in the hot water tank, thereby reducing consumption of gas which would otherwise be used to heat the hot water. The data recorded since then shows that 39.8% of the PV output would have been exported without the diverter. We have now reviewed the performance of the system after five years operation. The results of this review are summarised below;

Performance review data

Our specially developed domestic solar PV system performance simulator enables us to accurately simulate the performance of these systems with a range of solar PV, HW storage tanks and battery storage systems. The following assumptions have been made above;

1. Average gas boiler efficiency = 92.75%

2. Average CoP of heat pump = 3

3. Assumed % PV export with heat pump = 25%

We can use our simulator to look at the effect of increasing the size of the PV array by comparing the figures for different sized systems - please see below.

So, what happens if we add a typical battery – say 2.4kWh in capacity?

So, what about a 4.8 kWh battery?

Note: any inconsistencies in cost calculations is due to tariff fluctuations

And can we use the surplus to heat hot water?

The maximum daily surplus with a 1 kW PV system is 2.72 kWh. The daily energy demand for hot water is 5.9 kW, so yes, this works.

The maximum daily surplus with a 2 kW PV system is 8.92 kWh. This is more than the daily demand, so this won't work.

Alternatively we could try to improve the match between load and output by looking at the timing of the washing machines during the summer etc.

Turk Head

Mon, 06 Apr 2020 10:42:01 GMT

Domestic dwelling with roof and ground mounted PV panels

This converted cottage is situated just outside Skibbereen in County Cork. It has both roof and ground mounted PV panels and has served as a base for both experimentation and data collection for thirteen years.

Roof panels

The position of the panels at this location is a compromise (as with most locations). The panels are fitted as high as possible on the roof to maximise exposure to early morning sunshine because of a low hill to the east (a local micro-climatic effect), whilst keeping below the chimney to minimise partial shading in the late afternoon. Microinverters are used to optimise unshaded output and minimise the effect of the partial shading.

The measured system output was 1,850kWh/yr (6-year average). The PVGIS calculated shade free output for this system is 1,834kWh/yr. The partial shading by the chimney would have reduced the system output to c.1,819kWh/yr if a string inverter had been used instead of microinverters. This shows how losses resulting from partial shading can be minimised.

The logged output from this system was compared with various simulator outputs out of interest – see below.

This site benefits from several local micro-climatic effects that result in an increased annual output. These include low levels of daily convective and prevailing wind/relief cloud development because of proximity to the coast, frequent rain washing and moderate summer temperatures. The PVGIS figure appears reflect some of these benefits.

The roof mounted system was commissioned on 25th May 2007 – see full six years output below;

Coastal PV

This tracking system consists of six 160Wp Solarfun panels, total capacity 0.96kWp. It was installed on an exposed, west-facing hill close to the house in 2007. These panels produced 44% more output than fixed panels, but had to be replaced by a fixed system in 2010 because of concern about storm damage.

They are now ground mounted panels, which have a low environmental impact (they are supported by a locally grown larch support frame). They have been operating continuously since November 2007 and even survived a direct hit by near hurricane Ophelia in October 2017.

Electric Rayburn

One of the most interesting projects in the house at Turk Head, is the development of a high temperature thermal store/cooker/heater for use in conjunction with solar PV installations. The first stage of this project involved the installation of a set of resistive heating elements in place of the oil burner(s) in a Rayburn cooker and then controlling them with a MyEnergi EDDI diverter and the original cooker and boiler thermostats. Once converted, the previously oil burning oven is charged with excess solar output during the day and draws whatever is necessary from the grid to bring it up to the desired temperatures as and when required.

The 25 year old Rayburn unit was absolutely perfect - flawless enameled cast iron finish with a large covered cast iron hot plate with both burners in perfect condition. Unfortunately, the cooker was burning copious amounts of oil, but was in such good condition that it seemed unreasonable to decommission it .

In order to convert the Rayburn, electric heating elements and high temperature cabling and connectors were sourced and manufactured locally in Ballydehob by Ceramicx . The three 750 W elements in the photo heat the oven and a small air to water heat exchanger (the original Rayburn unit). A fourth 750 W element is located under the hot plate. The bottom element is on permanently - mimicking the original oil burner and keeping the house dry. The other three are controlled by an EDDI and the original cooker thermostats. It works slightly better than the original system as far as cooking is concerned. It is also providing space heating and hot water.

The plan is to increase its thermal storage capacity by filling it with ceramic "marbles" and also to install a few more PV panels to bring it close to being fully RE powered. The resulting reduction in CO2 emissions is c.3,450 kg per annum

The graphs below demonstrate clearly the financial benefits of PV panels on a domestic home. They illustrate the power load required to run the house, the amount of energy supplied by the PV panels and the total draw-down from the grid. All data was recorded using an iPhone! The device was used to get a two-day representative snapshot of electricity consumption at Turk Head over one weekend. After downloading the OSnap App, the interval was set to 5 minutes with the flash on and the phone was secured in front of the meter. The phone was then connected to a charger and left running away for a day and a half. The end result was 365 snaps of the meter, which provided exactly what was needed to calculate the value of the PV output. T his then showed that the PV system is reducing energy costs in the house at Turk Head by c.44% on unexceptional summer days.