Energy and Housing (eBook)

A Symposium Held at the Open University, Milton Keynes, on 31st October, 1974. Convened by B.W. Jones of the Faculty of Science and the Energy Research Group

H. J. Cowan, A. W. Hendry, C. B. Wilson (Herausgeber)

eBook Download: PDF | EPUB

2013 | 1. Auflage
158 Seiten
Elsevier Science (Verlag)
978-1-4831-3854-1 (ISBN)

Infos

Energy and Housing examines the problem of power for houses and energy for building materials and considers ways of reducing the energy consumed in domestic housing. Emphasis is more on the running energy costs than on the capital energy cost of building materials and construction. This book is comprised of 12 chapters and begins by describing two types of fluidic wall attachment devices for controlling hot water flow in a domestic heating circuit, followed by a discussion on the thermal performances of well-insulated houses having thermally heavy interiors and thermally light interiors and similar overall U-values. Subsequent chapters focus on how buildings provide protection from the climate and the problem of flexibility in thermal comfort; the energy cost of the construction and habitation of timber frame housing; the capital energy requirements of buildings; and the use of winter sunshine to heat buildings. A model that describes the thermal response of a solar heated building is also considered, along with the use of solar energy for housing and some problems associated with the design of low-energy housing. The final chapter evaluates the socioeconomic, environmental, and political implications of minimizing energy costs in buildings. This monograph will be of interest to energy and housing officials and policymakers.

Textauszug

FLUIDIC DIVERTER VALVES APPLIED TO INTERMITTENT DOMESTIC HEATING

Victor Ian Hanby, B. Sc., Ph. D., C. Eng., A. M. Inst. F.,     Department of Architecture, University of Nottingham, Nottingham

Summary

The application of two types of fluidic wall attachement devices is described for controlling the hot water flow in a domestic heating circuit. A flow circuit in which the hot water from the boiler is diverted either to the domestic hot water cylinder or to the space heating load is shown to have some potential for reducing energy consumption, when operated in the intermittent mode, relative to a conventional circuit in which the loads are met simultaneously. The devices described are of simple construction and would enable a diverting circuit to be specified in a dwelling with a small increase in the capital cost of the system.

It is commonly assumed that within a building’s overall energy balance the heating system may be regarded as a ‘black box’ with an overall efficiency which is usually assigned on the basis of the fuel used. In practice, varying the design of a certain type of heating system, for example a boiler serving hot water radiators and a domestic hot water supply, may have a significant effect on the running costs in terms of gross amount of fuel consumed, although the design heat loss of the dwelling be the same in each case. Very little information is available on the effect of variations in the engineering design of heating systems on the energy consumption of the dwelling. It is important that the heating system is matched with the transient thermal properties of the building and also the social patterns of the inhabitants. The control system plays an important part in achieving this objective. Any heating system must have some form of automatic control if advantage is to be taken of heat gains due to changes in climate and occupation of the interior space. Much more information must be made available on the transient characteristics of heating systems if the control of a heating system is to be optimised. Energy savings due to capital expenditure on control devices could then be calculated and an economic basis for expenditure on controls would be obtained in an analogous manner to that which is possible for insulation of the dwelling.

Intermittent Control

The most common control which is fitted to a domestic heating system is an electric time switch or ‘programmer’, which allows the system to be turned off once or twice a day if required. It is known that energy savings, from the point of view of heat input to the occupied space, can be made by intermittently heating the building (1), the savings (over a continuously heated building) being greater the lower the thermal capacitance of the structure. If a heating system is sized exactly to meet the steady state heat losses of the building with the appropriate external design temperature Td, under such conditions the inside temperature will take a very long time to get close to the desired value when the system is switched on. In the case of a hot water boiler serving a domestic hot water supply as well, the problem is even more marked. Sizing a boiler in this way means that even when T exceeds Tdthe system must be operated continuously. An outside temperature of 5°C has been suggested (2) as the lower limit for the intermittent operation of a system sized exactly to meet the design heat loss. A problem which is raised here is that the user must override the control device hence some of the inherent simplicity in the operation of an automatic control has been lost. Ideally a system should require minimal attention throughout the heating season. In addition to this there may well be some degree of reluctance on the part of the user to operate his system continuously day and night.

To enable the intermittent mode of heating to be utilised in cold conditions requires a certain amount of excess capacity. The degree of oversizing need not be so great as to involve the user in excessive capital expenditure, and certainly nowhere near as great as that commonly perpetrated by present day heating system installers. A preliminary investigation, using a mathematical model described below, indicates that if a diverting valve is used to separate the space heating load from the domestic hot water supply an excess boiler capacity of 30% based on the space heating load alone is the optimum for intermittent operation under design conditions. With the current availability of range-rated boilers this may frequently be achieved without incurring extra capital expense.

Sequence of Loads

A common method of providing a supply of domestic hot water and central heating from an automatic boiler is shown in Fig. 1.

Fig. 1 A Conventional Central Heating Circuit*.

The domestic hot water is heated in a storage cylinder by gravity circulation and water for the space heating is circulated by pump. A cylinder thermostat and a motorised valve may be used to stop the boiler water thermostat cycling when there is no demand for space heating. It is current practice to size the boiler for the two loads simultaneously, for example:

Space heating load

= 7 kW (design heat loss)

Domestic hot water allowance

= 4 kW

Total

11 kw

A margin would frequently be added to this and a boiler size of around 15 kW specified. This means that when the domestic hot water load is satisfied the boiler is working at only 50% capacity under design heat loss conditions.

One way of avoiding this situation is to ensure that the two loads cannot be coincident. Simultaneous demand for hot water and space heating in the morning is a possibility, because if full advantage is to be taken of intermittent control the system will have switched off before the occupants retire to bed. Useage of hot water after the switch-off time will mean that a simultaneous demand will exist in the morning. By diverting the pumped supply of hot water from the boiler firstly to the domestic hot water cylinder and then to the space heating load such a demand can be met with a reasonable excess boiler capacity. A number of systems are marketed on this principle. The ‘storage boiler’ heats the domestic hot water directly, heat is transferred from the water via a heat exchanger to the space heating circuit. Disadvantages of this system are the size and cost of a water heat exchanger capable of meeting space heating loads and the fact that the domestic hot water must be at a higher temperature than the water in the heat emitters. This is the reverse of the ideal situation and means that the size of the heat emitters must be increased.

A better, and more common technique is to use a diverting valve to transfer the pumped hot water from the boiler firstly into the domestic hot water circuit and, when that demand is satisfied, into the space heating circuit (Fig. 2).

Fig. 2 A Diverting Heating Circuit.

The only significant additional component to those in the conventional circuit of Fig. 1 is the diverting valve BA. A variation is available (3), where water regulations permit, which stores the boiler hot water with a considerable reduction in time required for the heating up of the domestic hot water side.

The question arises as to whether the energy savings due to running the boiler nearer to its rated output and the use of more compact pipe runs will be economically justified by the extra expense on the control devices required.

Fluidic Diverting Valves

Electro-mechanical diverting valves are quite expensive and some types of 3-port valves can suffer from hammering in a diverting application. Two types of fluidic diverter valve are being studied in this application which are potentially cheaper to manufacture than existing equipment. Fluidic controls use the energy and characteristics of the flow itself to effect the control function. The two devices shown in Figs. 3 and 5 are of very simple construction. The bistable (4, 5) of Fig. 3 is a wall attachment device that utilises the Coanda effect - the tendency of a jet to attach itself to a nearby wall. As the jet issues from the nozzle it ‘sticks’ to one wall or the other thus diverting the flow of water from the boiler either to the hot water load or to the space heating circuit. Switching is effected by applying a brief pulse of control flow taken from upstream of the nozzle into either of the two control ports. Switching requires a flow in the control port of about 2% of the main flow over a period of around 0.5 seconds, when the control flow may be discontinued. A good design of bistable may have a ratio of output pressure to input pressure of up to 45%. A major problem of the application of such a device is in transducing the electrical signal from the thermostat into the switching of the control flow. This is done at present by using a small electromagnetically operated spool valve (Fig. 4).

Fig. 3 Bistable Diverter Valve.

Fig. 4 Magnetically Operated Spool Valve.

Fig. 5 Monostable...

Produkt-Details

• Erscheint lt. Verlag: 22.10.2013
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik ► Bauwesen
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• ISBN-10: 1-4831-3854-2 / 1483138542
• ISBN-13: 978-1-4831-3854-1 / 9781483138541