Kirsty Burns
The aim of this essay is to investigate ways in which we can make central heating systems more energy efficient for single occupancy dwellings.
Energy consumption for heating
Firstly I would like to hypothesise that people living alone in single occupancy dwellings are better off not using traditional central heating systems. I calculated my own energy consumption to provide the basis for a case study. My annual gas consumption is 3750 kWh (13.32 GJ), primarily used during a five month heating season from about early-November to early April. Most of the hot water produced by the boiler is not used, so in the summer, the small amount of hot water required is obtained using electricity. The thermostat for the gas-powered central heating is set at about 140Celsius, which is considerably lower than most households: this is comfortable when occupants wear plenty of thermal clothing but since guests are generally reluctant to wear outdoor clothing throughout their visit, it is usually necessary to turn the thermostat up to at least 170C.
Over a year, the electricity consumption of the flat is 1200 kWh (4.3 GJ): the by-product of heat energy from the fridge-freezer, cooker, the use of electrical appliances (computer, television and radio) and compact fluorescent lighting will provide some �free� heating. Assuming half of this provides useable heat, I will get an additional 600 kWh (Rammage, 1997) 1 heat energy, and with a south-westerly aspect the flat will get a certain amount of solar gain, even during the winter. As this one bedroom flat has 70 metres floor space, we could estimate the overall energy consumption of 4950 kWh works out at 70 kWh/m2/year.
The energy consumption of the average UK household is 26,000 KWh (Rammage, 1997)1. The size of the average household is 2.67 people, and with 19,000 kWh used on heating, we can calculate the per capita energy use rate for my flat is favourable. However, for each 100 kWh, the combustion of natural gas results in 14 kg of CO2 released into the atmosphere. Therefore using 3750 kWh of gas is equivalent to 525 kg of CO2.
Maintaining thermal comfort and health
Although the UK�s energy consumption has fallen slightly since 1973, at around 8.7 PJ in 1993 it was more than 50% higher than it was in the early 1950s (Rammage, 1997)1. Approximately 2000 PJ can be attributed to low temperature heat requirements (heating and hot water). Before the advent of central heating systems, people would need to heat up the rooms we wanted to use. One room may have a temperature of 20-220C whilst the other rooms stay unheated unless required.
Advocates of central heating may argue that keeping the thermostat low is potentially unhealthy both for the occupant and the structure of the flat too: in cold and damp conditions the risk of fungi and mould growth increases. Indeed central heating is being promoted as an important tool to help curb winter excess deaths amongst the elderly (Scottish Executive, 2001) 2; it certainly may help, but to be truly effective, issues such as tackling fuel poverty and preventing heat loss by installing decent insulation, must not be ignored.
The low relative humidity created by central heating can cause also health problems. So I have started to investigate whether I can maintain or improve on my current energy consumption levels whilst safeguarding the property, and the health and thermal comfort of anyone visiting or staying in this type of dwelling.
Thermostats and TRVs
Basic central heating systems operate with a simple thermostat and timer. During the periods of time selected by the householder, the boiler will switch on and heat up the flat until the desired temperature is reached. With the thermostat located in the main living area room, appropriately located radiators can raise the temperature to desirable level fairly quickly, but unless other rooms have thermostatic radiator valves (TRVs) a lot of energy is wasted heating up other parts of the flat needlessly. Also, like many Islington dwellings built in the 1970s, my purpose-built flat does not have a traditional sloping roof. Fuel was considered plentiful and cheap until the energy crisis of 1973, and with the acute demand for cheaply built accommodation following the Second World War, resource conservation was low down the priority list for many years.
Figure 1: shows how central heating could be modified to allow for different temperature requirements in different rooms. The thermostat for the bedroom is set lower than the living room. When the relative humidity is high (over 70%) the heating switches on to guard against condensation & prevent mould growth
Flat roofs are used in warmer climates as an efficient means of losing unwanted heat; they aren�t ideal during the relatively cold winters we experience in the United Kingdom. There is no opportunity to change the type of roof, or reduce heat loss with loft insulation, and so to conserve fuel I believe it is best to keep radiators in unoccupied rooms switched off. However, during the coldest weather there is an increased risk of condensation and frost can lead to burst pipes, so it may be wise to set the thermostat to a low background temperature of around 150C (Healthy Homes Directory, n.d., website)3, (Save Energy, n.d., website) 4, , (Tendring, n.d., website)5. It is important to be aware of changes in weather conditions, especially if the flat is left unoccupied for several days.
Heating empty spaces
Many householders believe that it is better to maintain a comfortable temperature in their dwelling even when they leave it unoccupied for a week or more. Indeed, some heating companies say that, like the human body, it is beneficial for their customer to keep their heating system switched on all of the time: "By allowing the boiler to circulate water through the radiators at a constant rate, we can eliminate the ups and downs we feel as our heating system cycles on and off trying to catch up to the heat loss".
(Patterson, n.d., website) 6. However, it is arguable that keeping an unoccupied space heated continuously is wasteful (Bruce, n.d., website) 7, (Emory University, n.d., website)8 the building will lose heat energy constantly. In cold weather the thermal mass of buildings will retain some heat energy compared to air outside. This heat is gradually lost if the air temperature outside is cooler, but keeping the indoor temperature high does not mean any less heat is lost than if the room temperature is allowed to fall several degrees. It takes little time and no extra fuel consumption to raise the temperature back up from 150C to, say, 220C when it is required.
The question of heating unoccupied space applies when we look at a single person heating the whole of their flat. They can only occupy one room at any given time, so heating up the other rooms appears to be a waste of fuel, money and a unnecessary contribute to global carbon dioxide emissions? Energy efficiency centres advise people to switch off lights in rooms that aren�t being used: surely the same applies to heating. There is a time lag, but with moderately sophisticated central heating controls we can set the thermostat timer to switch on the heating in a room half an hour before we use it. It takes less energy to warm up a cold home in the morning than it does to maintain a constant temperature throughout the night.
Intelligent heating
New technology is being used to provide lighting that switches itself on when it detects the presence of people. When no movement is detected, the lights automatically dim and energy is conserved. A similar hi-tech solution can be applied to heating. e.g. Intelligent Comfort Systems9, the M.I.T. House of the Future10 or the Momentum home automation project:
The Intelligent Room Sensor measures the room temperature and transmits this data to the remote heating controller. It also allows access to the controller's most common functions, such as initiating daytime, nighttime or standby operation, indications of current time, room temperature and outdoor temperature, and setting trip-points for heating controls. (Esprit, n.d., website)11.
There is a large scope for the development of such technology in our homes (see also Rodgers12), although since people prefer to control their own environment I think it would be wise for intelligent system developers to provide manual override facilities.
Table 1
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Possible temperature plan for flat if TRVs and time-switches installed in each room
TimeLiving roomDining roomBed-roomKitchenBath
roomAverage from individual roomsAve flat temp. with tradnl CHTemp.
diffActivityHeated zone01:00 -
05:005555552015Sleep(Frost protection)06:00151515151515205Wake up*(Bedroom)07:00151515151815.6205Washing etc(Bathroom)08:00151518151515.6205Breakfast(Dining room)09:00 -
17:005555552015Work(Flat: background
heating)18:00151515151515205Cooking(Flat: background
heating)19:00151715151515.4205Supper(Dining room)20:00 -
23:00221515151516.420-2Evening(Living room)00:00151517151515.4205Go to bed(Flat: background
heating)Average temperature4.9320.0015.07Weather reports
An intelligent heating system could monitor the daily pattern of the occupant�s heating preferences, learning or remembering them� so that the desired level of temperature and humidity can be created automatically. When an occupant moves to another room it can be heated to a comfortable level in advance. Single heating zones can be replaced by full zone controls with separate pipe loops and thermostats: it is usually desirable to maintain a lower temperature when sleeping in a bedroom under a duvet than when spending a sedentary evening in the living room (Natural Energy, n.d., website) 13.
Figure 2 Possible temperature plan for flat
if TRVs and time-switches installed in each room to allow for individual heating control (see figures in table 1). Assuming the relative humidity is kept below 70% , reducing the risk of mould growth, the background thermostat could be set to 50C, saving on heating but protecting the flat against frost.
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Other aspects of �indoor weather� such as air movement and air quality could be measured and remedied through automatic adjustments of heating and ventilation, if necessary. The system could also provide weekly or monthly reports on energy use: a connection to the Internet, could allow access to weather forecasting information so that adjustments to heating patterns and fuel consumption can be prepared for.
Conclusion
A fully integrated hi-tech dwelling may still be some years away and, in any case, intelligent heating systems will not suit everyone. These days many of us are aware of the negative aspects of the controlled environments of air conditioned public buildings, especially if we are not permitted to control it ourselves, for instance by opening windows when we want. However, when we are given the choice, it may be worth exploring the options new technology can offer us if we cannot find a happy medium between traditional central heating and reverting to single space heating. Using readily available weather statistics for any area of the UK (for instance see the HYPERLINK "http://www.weather.co.uk" http://www.weather.co.uk website)14 we can calculate how much fuel is saved in heating rooms only when they are required. I believe we can make substantial savings to our heating fuel bills if we make a little more effort to avoid wastage by ensuring unoccupied rooms are not heated unnecessarily.
Bibliography and References
Rammage, J. (1997), Energy, A Guidebook Oxford
Scottish Executive New Appointment Signals Major Step Towards Central Heating for All Pensioners (2001) Press release SE2032/2001
www.healthyhomesdirectory.co.uk
http://www.savenergy.org/controls.htm
http://www.tendringdc.gov.uk/dampx.htm
Patterson, J. (n.d.) The Anatomy Of Selling Radianthttp://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,60301,00.html
Bruce, L.A. (n.d.) Energy-use myths exposed http://www.bankrate.com/brm/news/pf/20010223c.asp
http://www.learnlink.emory.edu/STUDENTS/Ecoseac/greenbook/energy%20guide.htm Green Book, Emory University
http://www.indoorweather.com/tech/comfheat_benefits.htm
Intelligent comfort systems
Massachusetts Institute of Technology (MIT) Home of the Future (ACHE Adaptive Control of Home Environment) http://www.web.mit.edu/is/isnews/v15/no2/15020.html
http://www.cordis.lu/esprit/src/results/pages/culture/cult11.htm (MOMENTUM project home automation modems developed by SGS-Thomson)
Rodgers, L., Etopian Vision http://www.cs.colorado.edu/~moser/papers/ieee.html
http://www.natenergy.org.uk/controls.htm (n.d.) National Energy Foundation
http://www.weather.co.uk
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