GB2344418A - A system for heating and ventilating a dwelling using a heat pump - Google Patents

Abstract

A system for heating and ventilating a dwelling comprises a heat pump 22 and insulating window shutters 1. The heat pump 22 provides heating and ventilation by delivering warm air 24 which may be dehumidified to a living room in the dwelling. The system also extracts air 28 from inside a bathroom of the dwelling thus controlling dampness. The living room may have apertures 26 to allow the warm air 24 to escape to the rest of the dwelling. The heat pump 22 may also recover heat and defrost itself using the extracted air 28. The shutter 1 may help to trap cold air between the shutter and the window and thus prevent it circulating into a room.

Description

HEATING AND VENTILATION OF DWELLINGS This invention relates to the reduction of energy consumption in the heating and ventilation of buildings, especially dwellings, by the use of insulating window shutters, heat pumps and dehumidification, to achieve acceptable Indoor air quality and control dampness and condensation.

Large quantities of fossil fuels are consumed for heating the current stock of buildings, and these are major sources of air pollution.

The likelihood of causing climate change by the increase of atmospheric concentration of C02 is compelling attention to ways of reducing emissions.

The technologies at present advocated for reducing fuel consumption in both new and old buildings are mainly : -air sealing of the building envelope, -roof and wall insulation, -control of heating and temperatures by time-switches and thermostats, -efficient conversion of energy by gas condensing boilers, -recovery of heat from outgoing air by heat exchangers.

However these are based on largely unjustified assumptions, and do not address directly the two primary purposes of space heating in houses, which are : -to keep people thermal comfortable, that is feeling neither too cold nor too hot.

-to help keep houses dry. Both heat and ventilation are needed to carry away the moisture which evaporates continuously in every house from domestic activities and in old houses also from damp walls and floors. Unless this is removed it will condense in colder regions.

Much fuel is wasted through shortcomings in current heating and ventilating practices : -Present ventilation practices do not satisfactorily reconcile the often conflicting requirements of thermal comfort, removal of contaminants, provision of combustion air for appliances, and conserving energy.

-Traditional ventilation via openable window vents, results in piercing draughts across a room and stratification of cold air at low level, impelling people to close vents.

-Air sealing as required by UK Building Regulations is likely to reduce adventitious ventilation to below the rate needed to carry away domestic evaporation.

-Present advocacy of naturalw ventilation is mistaken. Fan control is required to ensure a necessary minimum rate of ventilation while avoiding excess, and to recover the heat in outgoing stale air.

-Mechanical ventilation at the rate provided by typical heat exchangers is inadequate. When the external temperature is 5C the internal dewpoint will be about 14C, resulting in condensation in bedrooms or roof spaces colder than that.

-Anyway, ventilation is an Inefficient way of controlling condensation. External air In winter is nearly saturated so has little capacity for carrying away moisture unless heated. A high rate of ventilation is thus needed in a poorly heated house.

-Dehumidification has more potential, but typical domestic dehumidifiers are very inefficient and condense only a small fraction of their theoretical potential. Though a heat pump they operate in a closed system, so produce heat equivalent only to electricity consumed.

-Time-switched heating aggravates condensation. Surges of moisture evaporate from heated rooms and condense in cooler bedrooms and roof spaces.

-Fuel consumption is being increased by present practices. Most housing associations have been tmpetted to install full heating In their properties in trying to control bedroom condensation caused by misguided draughtproofing.

-Heating appliances such as gas and coal fires, electric radiant, convector and storage heaters, and even hot water radiators are usually located on internal walls, where they are less effective In achieving comfort. Heat sources ought be located beneath windows to counteract downdraught.

-Surfaces of most heating appliances are too hot and too small, producing too-hot air which rises rapidly to ceiling level, where it loses heat to the ceiling, before eventually descending to people levei.

-Fierce radiant heat is needed to compensate for the discomforts of cold walls and draughts caused by present practices -Condensing boilers do not develop their full efficiency unless the retum water temperature is cool enough to condense the flue gases. Improving the insulation of a house may thus reduce the efficiency of the boiler.

-Open flued combustion appliances are required to have a'safety vent"ostensibly to ensure adequate combustion air. But when wind blows from the opposite side of a house, air is sucked from the safety vent, which may depressurise the house, causing a back draught and leakage of flue gases likely to contain carbon monoxide and loaded with water vapour if from gas. Such"safety"vents can thus actually create a hazard, as well as causing cold draughts, condensation and wrecking ventilation control.

-Much coal is stiil burnt domestically, especially in small towns and rural houses where gas is not available. But there are numerous sources of inefficiency in domestic stoves and coal cannot be burnt efficiently. Incomplete combustion results in obnoxious local pollution by tars, carbon monoxide and sulphur dioxide.

-Pollution, hazards and inefficiencies make domestic buming of any fuel burning inappropriate. Much higher overall efficiencies would be obtained if all fuels were burnt in power stations and the electricity used to drive heat pumps. These can produce at least three times as much heat as electricity consumed, uprating the effective efficiency from a net 30% for old power stations to 90%. Gas bumed in local combined heat and power plant could likewise achieve over 200% primary energy efficiency.

-Electricity tariff structures discourage use of heat pumps, because electrical heat can be bought as cheaply by night storage heaters at a third of the standard tariff.

-There is little incentive for most people to save energy at current prices of fossil fuels. Fuel costs are a small part of expenditure of most households. An energy tax replacing most existing taxes, to increase fuel prices to nearer the true value of irreplaceable resources would provide an incentive to reduce fuel consumption, and have far-reaching benefits in other directions.

-Full upgrading of houses including extemal insulation, costing over 10, 000 is not cost effective to private householders at current energy prices. Moreover approprate knowledge and skills are scarce in Britain, while the'planning"system can prevent upgrading.

There is thus no prospect of substantial reduction in housing energy through the present administrative, fiscal, economic, and technical frameworks.

The present invention provides coherent solutions to all the above problems and conflits, with equipment which can be factory mass-produced and quickly fitted to almost all existing houses.

A spread sheet shows useful energy input reduced by over 90%, without double glazing or wall insulation. At a capital cost of probabty less than 3000 per house it is likely to be cost effective without need for govemment subsidy, and thus enable the market mechanisms to make rapid progress with C02 reduction.

It should also improve thermal comfort and heatth, reducing hypothermia and asthma, and preserve building structures. Such a partial heating system which at very low fuel cost effectively controls dampness and mould, is believed would provide"95% thermal satisfaction'for most households and thus be very acceptable to the market.

Funding capital installations with commercial loans should be cost effective, certainly for housing associations, which incur high costs in management, maintenance, and legal liability theugb caused by condensation and gas hazards.

In its full manifestation, a new type of insulating window shutter first reduces the heat loss of a house by about as much as watl insulation and double glazing.

A small heat pump operating 24 hours a day, can then provide enough heat to keep the main living room warm 24 hours a day, and ventilate the rest of the house.

The heat pump combines basic heating and ventilation as pre-warmed fresh air, supplied by a heat pump to the living room, maintaining it at a comfortable temperature 24 hours a day. The warm air overflows from the living room to convey ventilation and some background warmth to the rest of the house.

Top up heating to other rooms can be provided where desired with low-powered electric resistance heaters, an existing heating system or by additional heat pump units.

The fresh air input to a house can be taken either direct from the exterior, or from downstream of the cold heat exchanger of the air source heat pump, thus being partly dehumidified.

By removing some of the 30 kg/day of moisture already in the air passing through a house at the minimum ventilation rate of about 50 litres/second, the capacity of air to absorb and carry away house moisture is Increased. This is particularly valable for damp old houses. The air Is re-humidified by moisture evaporating within the house.

Fresh warm air supplied to the living room will displace contaminated air through holes elsewhere in the building envelope. In a partly heated house, much of the heat in the escaping air will have been recovered in slightly warming the structure of the house.

Air is preferably extracted continuously from the bathroom and ducted back to the heat pump unit where it usefully defrosts the evaporators while heat Is recovered. This is desirable whether or not there Is much heat to recover, or whether the house is well heated or sealed.

Contrary to common practice, air should be extracted from low level in a bathroom because air becomes denser as it is cooled by water evaporating adiabatically from drying towels, clothes, walls, and floors.

For easy installation in existing houses, ducting needs to be minimised. Drawing not b shows an arrangement which will suit many houses. The heat pump unit is housed in a purpose-made porch roof, which should make it aesthetically acceptable. From here ducts along the corridor ceiling can readily reach any part of a house.

Energy reduction, sachleved in several novel ways: -The new type of insulating window shutter can reduce heat loss by more than double glazing and wall insulation put together. Fitted only to the living room windows, which are the least insulating elements of the best heated room, they are the most effective form of thermal insulation.

-Fitted also to other windows In a house, shutters can raise the background temperature achieved by the percolating warm air by about 3C. With dampness controlled, and a good background temperature supplementary heating is less needed in bedrooms etc.

-Using the output of a heat pump to pre-warm incoming cold fresh ventilating air achieves a higher coefficient of performance, of 5 or more compared to less than 3 for conventional air conditioners or heat pumps heating water to say 50C for use in radiators.

-Defrosting the heat pump with exhaust warm air alternating with external air between two evaporators avoids consumption of energy for defrosting.

-The rate of ventilation necessary to control condensation is reduced by the optional partial dehumidification of the input air.

-Ventilating with dehumidified air allows an air sealed house to be partially heated. Otherwise houses need full heating to control condensation.

-Continuous heating uses the heat input to best effect in keeping a house dry and people thermally comfortable.

-The technology is better able to cope with the leakiness of UK houses. Continuous supply of gently warmed air maintains better background warmth in a house than distributing the same quantity of heat in conventional ways more subject to loss.

This invention thus incorporates a cascade of successive energy reductions, which enables a low powered heat pump to provide sufficient heat, conveyed without excessive temperature of the ventilating air flow to provide comfort heating in most weather conditions.

This heating and ventilating unit actually conditions air in changing its temperature and moisture content. However it differs from conventional air conditioners in several respects: -Residential air conditioners are mainly designed for summer use to achieve cool internal conditions where external temperatures are uncomfortably high. By contrast this invention is almed at energy efficient winter heating.

-Heat pumps and air conditioners have not been attractive for heating in the UK because at a coefficient of performance of less than 3, the heat produced is more expensive at standard electricity tariff than from gas or night storage heating at one third of the day tariff. However, using the output in the above ways makes heating much cheaper than the competition.

-Dehumidification by conventional air conditioners is associated with summer cooling in hot climats. Otherwise cooled external air can be near 100% relative humidity, which is felt as'close"and sweaty. In winter, conventional practice is to humidify, to avoid low internal relative humidities where external air is very cold and thus dry. But excessive dryness is not a problem in the relatively mild UK winter conditions. The common problem in dwellings is excessive humidity, condensation and structural dampness in old houses. This invention dehumidifies the incoming air in winter.

-Conventional domestic dehumidifers operate in a closed system and thus produce heat only equivalent to electricity consumed, and are otherwise very inefficient. This system of using the chilled air from the heat pump produces dehumidified air at very little energy cost.

-Residential air conditioners mainly re-circulate the same air, relying on adventitious infiltration to provide necessary fresh air. Only a few provide a fresh air component. Systematic ventilation is needed in air sealed houses to adequately control moisture, household odours, carbon monoxide and radon. The 100% fresh air is most appropriate for domestic applications.

-Heat pump heat recovery units are available, but these do not add heat extracted from an external source, or have any dehumidification function.

-Conventional air conditioners and space heating heat pumps both use relatively powerful compressors. In this invention the compressor can be low-powered because: a) The higher COP enables a smaller compressor to be used for the same heat output. b) The continuous heating concept avoids the need to heat a house quickly from cold. c) The dehumidification function allows a house to be partially heated. d) Heat losses are reduced by the dehumidification function, partial heating, window shutters and heat recovery.

According to the present invention there are provided: FirstlyaR-insulating window shutters to heated rooms in a building, of a new design which allows partial opening for vision and dayiight without losing all the insulation value of the shutters.

Secondly, a heating and ventilation unit comprising a heat pump, heat exchangers and various controls and air handling devices designed and arranged to take in, cool and thereby partially dehumidify external air. A variable proportion of this can be rejected direct to the exterior.

The heat thus extracted from a relatively large volume of external air is used to warm a smaller volume of either a proportion of the chilled air, or a supply of uncooled air if dehumidification is not required.

The pre-warmed fresh air is delivered to the one or more rooms where heat is most needed. The heat pump is controlled to maintain the main room at sitting comfort temperature.

The flow of warm fresh air into these rooms displaces an equivalent flow of air through gaps around internal doors or purpose made vents to the corridor, from where it convects to other rooms and may be displaced to find its own way out through adventitious or purpose made vents in other rooms in the building envelope.

Optionally, a part of the heat content of the outgoing air may be recovered by extracting it from one or more bathrooms and ducting it back through a second evaporator in the heat pump.

Most commonly the heat pump consists of an electric motor driving a compressor which liberates the latent heat of liquefaction of a working fluid, which after passing through an expansion device, evaporates, cools and absorbs heat from the surroundings. Other devices are available which can serve the same purpose of pumping heat from a cold place to a warmer place.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a vertical sectional elevation of a window set in a cavity wali, fitted with insulating shutters.

Referring to the drawing, the lower shutter 1 closes vertical upwards to enclose between itself, the glass 2 and adjacent structure a space 3 which is separated from the remainder of the room air by close fitting joints, except at its upper boundary 4. The air within this space in cold weather cools by contact with the cold glass surface. The cold air being denser than the warmer room air cannot convect out from this space. Room air can convect only against the glazed area 5. In this way the high heat loss through glazing is reduced approximately in proportion to the area covered by the insulated shutter.

The upper shutter 6 counterbalances the lower shutter 1 for compactness, and both are shown in a partly closed position allowing some vision and daylight appropriate to a cold day. At night, the two parts are closed together, to fully shutter the window opening. The guides 7 are fixed to and sealed to the wall.

Figure 2 shows in diagrammatic form the air flows of the heating and ventilating unit.

Fresh air is induced from the exterior through a filter 8 by a fan 9 to flow over a cold evaporator 10 of a heat pump, which cools and partly dehumidifies it. A part of the flow is rejected at 12.

The fresh air which is to be supplied to the dwelling may be selected by a valve 21 to be either non-dehumidified air taken directly from downstream of the fan 9, or a proportion of the chilled and dehumidified air. ff the latter it passes through a heat exchanger 13A where it is warmed slightly by the incoming external air, which is itself also slightly cooled, both reducing the work to be performed by the heat pump. The air supply is further warmed by heat exchanger 13 carrying exhaust air from the bathroom induced by fan 14. The temperature of the air is further raised by passing over a warm condenser 15 of the heat pump and then over the compressor unit 16, from where it is ducted into the dwelling at 17.

For greater energy efficiency, a second evaporator element 11 in series with 10 is provided, over which passes a fiow of exhaust air, from which heat is extracted before being ducted to the exterior.

For the purpose of energy efficient de-frosting, boxes 18 and 19 contain vanes which are mechanically actuated simultaneously to interchange the air flows, such that exhaust air flows over evaporator 10 and fresh air over evaporator 11. Also simultaneously, a valve 20 reverses the flow of fluid such that in each mode, the working fluid passes first through the evaporator over which fresh air is passing and then through the evaporator passing exhaust air. The air flows are alternated automatically, and in this way the evaporators can be defrosted in average weather without expending additional energy. A standard defrosting mechanism not shown is also fitted to ensure that the evaporators can be defrosted in any weather conditions.

Figure 3 shows a vertical cross section of a house. lnsulating shutters 1,6 are fitted to the windows.

The heating and ventilating unit 22 may be conveniently housed in the roof of a purpose-designed porch 23. A duct 24 passes through the house wall and delivers partiy dehumidified warm fresh air to low level near the window of the living room.

An opening 26 may be made in a wall to allow room air to be displaced into an adjacent room 27. Such an opening may have an intumescent or other fitting to close automatically in the event of fire in the living room.

Room air is eventually displaced through gaps 25 around the door of the living room or other purpose made openings into the circulation spaces.

Air Is extracted by the heating and ventilating unit through duct 28 from the bathroom 29, inducing a general flow through the circulation spaces.

Ventilation of individual rooms can be increased by providing an opening 30 above doorways to increase convection from the circulation space.

The rate of extraction is less than the rate of supply of air, thus maintaining the house at a positive pressure, reducing the risk of flue gas leakage and entry from the ground of radon, methane from landfill or sewers, and mains gas from pipe leakages.

A positive pressure causes the excess to be displaced through residual holes in the building envelope.

After systematic ventilation has been provided by this invention, windows and doors can be air sealed.

Claims (9)

1. CLAIMS 1. A system for upgrading buildings to save energy, control condensation, improve air quality and thermal comfort comprising a combination of thermally insulating window shutters and a heat pump which provides both heating and ventilation by delivering warm fresh air to the building.
2. 2. A system as in J'in which the shutters are constructed to fit closely to the adjacent structure such as to substantially prevent the escape of air from the space so enclose between such shutters and glazing except at the open upper edge in the case of a lower shutter. The lower or only shutter closes upwardly, thereby in cold sunless conditions retaining a well of cold air between the lower shutter and glazing so preventing the convection of warmer room air against the glazing, and enabling the shutters to be partly opened for vision or daylight while substantially retaining the thermal insulation value of the lower shutter.
3. 3. A system as claimed in 1 or 2 wherein the heat output of the heat pump heats incoming cotd air, whereby a high coefficient of performance is obtained.
4. 4. A system as claimed in 1,2 or 3 so arrange as to deliver fresh warm air to the main living room of a dwelling, from which suitable apertures are provided to allow such air to escape through the rest of the house
5. 5. A system as claimed in 1,2,3 or 4 in which the heat pump can also partly dehumidify the air delivered to the building thereby increasing its drying properties and reducing the ventilation rate necessary to remove moisture from the building.
6. 6. A system as in claim 1,2,3,4 or 5 in which the heat pump is designed also to extract contaminated air from a building, to defrost itself with such air and to recover heat from the contaminated air before rejecting it to the exterior.
7. 7. A system as in claims 1,2,3,4,5, or 6 so conneded to extract contaminated house air from low level in a bathroom, to where air falls which has cooled by adiabatic absorption of moisture, thereby removing moist air efficiently and allowing a bathroom to be heated without concurrently removing recently warmed warm air from higher level.
8. 8. A system as in claims 1, 2,3,4,5,6 or 7 wherein the heat pump is located within the roof of a porch thereby minimising duct lengths, visual unacceptability and nuisance from noise and discharge of cold air.
9. 9. An system for upgrading buildings comprising a cascade of interdependent and integrating synergistic energy-saving features, whereby heat losses are reduced by: -window shutters as in claims 1 and 2; -providing a combination of heating and ventilation as in claim 1; -and with 24 hour operation ; -enabling a relatively small heat pump to be used as a heat source, and to further reduce energy consumption by exploiting the function of a heat pump by -utilising the heat output of the heat pump to heat cold fresh air, thus obtaining a high coefficient of performance as in claim 3; -defrosting itself with outgoing air as in claim 6; -recovering heat from outgoing air as in claim 6; -dehumidifying the supply air as in claim 5, which allows reduction of ventilation rate; -air sealing and partial heating as in claim 4 without causing condensation ; thus improving air quality, controlling dampness and thermally safisfying the occupants with relatively little expenditure of energy and providing a practicable means for rapidly reducing the global emissions of C02 caused by buildings.