GB2423569A

GB2423569A - Electrical thermal storage combi boiler

Info

Publication number: GB2423569A
Application number: GB0503537A
Authority: GB
Inventors: Nicholas Julian Jan F Macphail
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-02-21
Filing date: 2005-02-21
Publication date: 2006-08-30
Anticipated expiration: 2025-02-21
Also published as: GB0503537D0; GB2423569B

Abstract

A thermal storage combi boiler primarily heated electrically has its control valve/s (7) and pump/s (6) situated in the return pipework to reduce the heat stress they would be subjected to on the flow pipework while enabling the flow to the heat exchanger (5) to be drawn from the top of the store (1). The flow to the central heating circuit (8) is drawn from lower down the store (1) to effectively form a thermal reserve for hot water production above this flow tapping (8) for hot water production to continue even when the actual heating production has lowered the stored water temperature in the store below the flow tapping (8). Hot water is provided to taps via the heat exchanger and conduit (11).

Description

THIS INVENTION RELATES TO IMPROVEMENTS IN ELECTRICALY HEATED

THERMAL STORAGE COMB! BOILERS It has become common practice with gas and oil fired boilers to use a thermal store together with a plate heat exchanger as shown in patent No 2266762 to provide mains fed domestic hot water. This arrangement has advantages over non storage arrangements, for example, gas fired non storage combi boilers in that a far greater short term flow rate to taps of hot water is achievable from a storage combi for a given instantaneous boiler load.

With the increasing importance of the "alternatives" to burning carbonbased fuels electricity, perhaps surprisingly given the comparative inefficiencies of its generation and distribution, becomes a sensible alternative to the remote or local burning of carbon- based fuels. These advantages stand out when electricity is used for heating and hot water supply with a thermal storage device, as the thermal store allows the input of heat energy to be suspended at times of peak demand while the thermal store's output to provide space heating and hot water can continue.

The storage combi is attractive to the generating companies because most of the alternatives to burning carbon-based fuels (for example nuclear, wind, and tidal generation) cannot be switched on or off instantly to suit demand. Although remarkably useful to meet base loads, these "alternatives" have not been favoured by the generating : * companies as they cannot meet unexpected (or indeed expected) peak load demand.

Electric thermal storage devices, like electric thermal storage combis, that can have their * loads remotely switched off by the generating companies' during times of peak load provide a good means of providing a flat base load while offering the option of peak load shedding needed by the generating companies to make best use of the "alternatives".

: * Electric storage combis are thus more financially attractive to the generating companies and have attracted special charge rates to encourage their use. These lower charge rates, in turn, make electricity more attractive than burning carbon-based fuels and will help : * * with the reduction of carbon emissions required in the Kyoto agreements. I* S

* 5: Thermal storage combis will help to reduce the use of the finite carbon-based fuels used in the supply of domestic heating and hot water to peak load needs only.

It has been common practice to use direct firing of carbon-based fuels (commonly gas or oil) into storage combi boilers to provide heating and better hot water flow rates. This use of storage combis while providing heating and good flow rate hot water to domestic premises adds to the use of carbon-based fuels requires a flue that adds to air quality problems and cannot benefit from the growing use of alternatives.

In one currently available form of electric storage combi boiler a copper cylinder is provided with a mains water fed copper chamber within the water contained in the copper cylinder. The mains water fed copper chamber acts as a heat exchanger and small thermal store for hot water supply. This type of unit is not suitable for unvented use of the thermal store and because the heat exchanger is built into the thermal store requires the entire unit to be replaced if the heat exchanger fails. The entire unit also has to be replaced if the thermal store fails.

Other types of mains storage combi boilers propose that the thermal store is provided with its main source of heat from a carbon fuel powered boiler with an immersion heater for stand by hot water supply only. This type of unit cannot be used as an electric only combi unit as its electric input is designed to provide minimal back up in the event of main heat source failure. This type of unit cannot be usefully used by the generating companies for load levelling and would not therefore benefit the end user with lower tariffs.

It is the aim of the present invention to improve on or obviate the abovementioned problems.

According to the present invention there is provided an electrically heated combi boiler system comprising a heat exchanger for providing mains fed domestic hot water fitted externally to and drawing its heat energy from a thermal store designed to be mainly heated by electricity, said thermal store acting as a heat source and thermal reservoir for :. : providing heated water to a heating system and or mains fed domestic hot water. S...

In a preferred form water is drawn from the thermal store for central heating and or to *: * provide domestic hot water via a heat exchanger.

:. Advantageously water is drawn from the top of the thermal store to provide hot water to tap via a heat exchanger but water for central heating is drawn from lower down the :. * thermal store to conserve a thermal storage reserve above the central heating draw off * point to permit continued hot water supply during times of electric supply interruption by * . the electricity supply company.

In a preferred form the thermal store is formed by a cuprous vessel.

In a further preferred form the thermal store is formed from a noncuprous vessel.

Preferably where thermal store strength permits the expansion of water within the thennal store and any heating system it may serve is accommodated by an expansion vessel together with the filling and safety pressure relief valve as would be used in an unvented boiler.

Alternatively a conventional cold feed and vent tank arrangement may be used to provide safety relief and to accommodate expansion of water within the thermal store and any heating system it may serve as would be used in a vented boiler.

Each of the preferred forms incorporates electrical elements controlled by thermostats as their main heat source.

Advantageously time delay switching of each of the electrical elements is incorporated to minimise reactive spikes being caused to the mains electrical supply.

Conveniently additional tappings for heat energy input from alternative sources such as solar panels may be incorporated in the thermal store.

Preferably the thermal store is provided with an external heat exchanger having a shunt pump to assist circulation of the primary thermal store water through one side of the heat exchanger while mains water flows through the other side of the heat exchanger to be thus is heated for domestic hot water use said shunt pump being actuated by the detection of flow of mains water to provide domestic hot water.

Advantageously a thermostatic mixing valve is provided to permit safe temperatures of domestic hot water to be delivered to tap while permitting high storage temperatures to increase the thermal storage effect.

Conveniently the thermal store incorporates a control system that provides flow of hot water from the thermal store to the heating circuits and or the heat exchanger using commonly available motorised valves, pumps, thermostats and time switches.

* : . In order that the invention may be more readily understood and so that further features * : * may be appreciated the invention will now be described by way of example with * reference to the accompanying drawing which is a diagrammatic representation of an * * . unvented form of the present invention wherein: A thermal store 1 contains a primary medium (normally water, containing a proprietary reaction inhibitor) heated by immersion heaters 2 and 3. Tappings (not shown) for the input of the flow/s and return/s from alternative heat source/s e.g. from solar panels may be incorporated within the thermal store.

After the thermal store I has been preheated by the immersion heaters 2 and 3, when the flow detector 4. senses water flow through the heat exchanger 5 caused by a hot water demand, the motorised valve 7 is actuated to close its port to the heating system, (not shown) that is serviced by flow conduit 8 and return conduit 9, and open its port to the heat exchanger 5. The pump 6 is simultaneously actuated to draw thermal store water through one side of the heat exchanger 5 while cold mains water is heated as it flows through the other side of the heat exchanger 5 whereafter the tempering valve 10 regulates the water temperature passing to taps via conduit 11.

Having satisfied the demand for providing domestic hot water to taps by the above- described means, assuming that there is no central heating demand from the controls (not shown), the motorised valve 7 and pump 6 are shut off.

Should there be a demand for central heating from the controls (not shown) the motorised valve 7 is moved to open the port to the central heating return conduit 9 while closing the port to the heat exchanger 5. As is common with combi boilers the controls are configured as priority to hot water and thus in the present example the three port valve would be a diverting valve rather than a mid position valve, although if system volumes and conditions permit this should not be taken as precluding the use of flow sharing systems.

In addition to the above-mentioned controls there are shown the components normal to an unvented combi boiler namely a mains water inlet 12 leading to a pressure regulating valve and pressure relief valve 13 discharging via a tundish 14 to a safe discharge point.

Downstream from the pressure regulating valve is a flexible filling loop 18 together with a pressure gauge 17, an air vent for removing system air 20 to facilitate initial system filling/topping up evaporative gland losses and an expansion vessel 15 to accommodate the varying thermal store and heating system water volume as it heats and cools. A factory fitted temperature and pressure relief valve 16 able to discharge via tundish 19 to safe discharge is incorporated to meet current regulations. S...

As the total electrical loading of the immersion heaters in this type of electrical storage combi is high, typicallyl2Kwatt or more, it is normal that the thermostatic control would : be linked to a time delay system so that each immersion element would be switched on * with a delay before the subsequent elementls switching takes place to avoid a transient spike caused by all elements being switched at once. This arrangement is known and has not been shown.

* . : Although for the purposes of description an unvented system has been outlined this does * not preclude a vented arrangement with integral or remote cold feed and vent tank.

Although a system using a three-port valve on the system return has been described this does not preclude the use of multiple two-port valve multiple pumps whether on the flow or return.

Although the above system has been described as having the outlet from the store to the central heating placed some way from the top of the thermal store to leave a reservoir for hot water demand above the outlet this does not preclude the siting of the outlet to the central heating at the top of the thermal store.

The thermal store may conveniently be formed by a commercially available stainless steel unvented cylinder preferably having a capacity of greater than 100 litres. This capacity may usefully be increased to provide greater instantaneous flow rates to taps and greater thermal reserves against longer periods of supply interruptions.

The heat exchanger may conveniently be formed by a commercially availably brazed stainless steel plate heat exchanger.

All the other components described above may conveniently be those commercially available for use with unvented, mains fed cylinders. * S. *. . S.. S **SS * S * S. S * . S * ..

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Claims

CLAJ1SAS 1. A device where there is provided an electrically heated combi

boiler system comprising a heat exchanger for providing mains fed domestic hot water fitted externally to and drawing its heat energy from a thermal store designed to be mainly heated by electricity, said thermal store acting as a heat source and thermal reservoir for providing heated water to a heating system and or mains fed domestic hot water said heated water is drawn from the top of the thermal store to provide hot water to tap via a heat exchanger but said heated water for central heating is drawn from lower down the thermal store to conserve a thermal storage reserve above the central heating draw off point to permit continued hot water supply during times of electric supply interruption by the electricity supply company, a three port motorized valve and circulating pump is located on the return pipework to permit the stored water to be drawn from two different positions on the thermal store while advantageously subjecting them to the lower return water temperature that has been shown to extend their lives.
2. A device according to claim 1 where the control is by two zone valves and one pump located on the return pipework.
3. A device according to claim 1 where the control is by two pumps located on the return. * I* * I I *ISI

* . ..
4. A device according to claim I where the thermal store is formed by a cuprous vessel.

*
5. A device according to claim I where the thermal store is formed from a non-cuprous vessel.
6. A device according to claim Iwhere the thermal store incorporates a control system * that provides flow of hot water from the thermal store to the heating circuits and or * the heat exchanger using commonly available motorised valves, pumps, thermostats *. .: and time switches.