Space heating

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Space heating

  1. 1. Space heatingAchieving interior thermal comfort in a cold climate Royal Agricultural College
  2. 2. What is space heating?• Technical term for providing heat to raise the internal environmental temperature.• Space heating can be achieved with stand alone heaters, e.g. open fire places: local heating• More efficiently achieved with a single heat source which distributes heat round the building using a heat Royal Agricultural transfer medium: central heating College
  3. 3. Open fires: nice but… you need lots, they are dirty, uncontrolled, need constant fresh airCentral heating: one heat sourcewith a heat distribution system.Complicated but controllable Royal Agricultural College
  4. 4. Why do we need it?• Good question –By careful design and building management it is almost possible to manage without it. Royal Agricultural College
  5. 5. “Laws” of thermodynamics• Heat flows from a hot body to a cold body until the two are at equal temperatures – Understanding and controlling heat flow is the key to space heating design• Energy can neither be created nor destroyed. It can only change forms – Managing sources of energy, in different forms, is the challenge of Royal space heating design Agricultural College
  6. 6. Basics of heat flow Royal Agricultural College
  7. 7. Basics of heat flow Royal Agricultural College
  8. 8. Basics of heat flow Barrier to heat flow: Insulation Royal Agricultural College
  9. 9. Controlling heat loss• Reducing heat loss through the building envelope reduces the need for space heating.• The thermal conductivity of a wall, floor or roof enclosure is called its “U” value – Watts of power lost per square metre for each degree centigrade temperature difference: W/m2 OC Royal Agricultural College
  10. 10. U value in practice Inside temp 10 OC Difference in 1m2 of wall temperature between inside and outside is 1OC The amount of heat travelling through one m2 of wall is the U valueOutside temp Acceptable U values: 9 OC Walls - 0.35 W/m2 OC Roofs - 0.16 W/m2 OC Royal Agricultural College
  11. 11. U value calculation for a wall plaster • Thermal resistivity of 1 m2 for blockworkinsulation 1mm thickness of each material in wall found from published data • Resistivity multiplied by actual thickness of materials • All resistances added, plus theoretical resistances for boundary layers of air, to give total thermal resistance of 1 m2 wall = R • Reciprocal of R = 1/R = U value • Must be 0.35 W/m2 OC or less to satisfy current Building Royal brickwork Regulations Agricultural College
  12. 12. Heat loss calculation• Wall area = 500m2 U value = 0.35 W/m2 OC loss =175W OC Roof area = 100m2 U value = 0.16 W/m2 OC loss = 16W OC Royal Agricultural College
  13. 13. Heat loss calculation• Wall area = 500m2 U value = 0.35 W/m2 OC loss =175W OC Roof area = 100m2 U value = 0.16 W/m2 OC loss = 16W OC• The external “design temperature” in England is -1OC The internal design temperature is what you want, say 22OC Temperature difference is 23OC Royal Agricultural College
  14. 14. Heat loss calculation• Wall area = 500m2 U value = 0.35 W/m2 OC loss =175W OC Roof area = 100m2 U value = 0.16 W/m2 OC loss = 16W OC• The external “design temperature” in England is -1OC The internal design temperature is what you want, say 22OC Temperature difference is 23OC• Heat loss through walls = 175 X 23 = 4,025W Heat loss through roof = 16 X 23 = 368W Total heat loss = 4,025 + 368 = 4,393W approx 4.5KW Royal Agricultural College
  15. 15. Heat loss calculation• Wall area = 500m2 U value = 0.35 W/m2 OC loss =175W OC Roof area = 100m2 U value = 0.16 W/m2 OC loss = 16W OC• The external “design temperature” in England is -1OC The internal design temperature is what you want, say 22OC Temperature difference is 23OC• Heat loss through walls = 175 X 23 = 4,025W Heat loss through roof = 16 X 23 = 368W Total heat loss = 4,025 + 368 = 4,393W approx 4.5KW• Disregarding floors, windows, doors etc. this house will need a space heating input of about 4.5KW to keep it warm on a cold Royal Agricultural English winter’s day College
  16. 16. Environmental heat input• The space heating system is not the only source of heat. – 100W bulbs produces about 80W of waste heat – A sedentary person produces about 100W of heat – So if there are four people reading by the light of 4 light bulbs, they are producing about 780W of heat, say roughly 1KW• The boiler only needs to make up the 3.5KW difference Royal Agricultural College
  17. 17. The law of unintended consequences• We are being encouraged and required by central governments to change heat producing lights bulbs for lower energy replacements. Royal Agricultural College
  18. 18. The law of unintended consequences• We are being encouraged and required by central governments to change heat producing lights bulbs for lower energy replacements.• This saves around 1.5KW of electricity needs for lighting in a house Royal Agricultural College
  19. 19. The law of unintended consequences• We are being encouraged and required by central governments to change heat producing lights bulbs for lower energy replacements.• This saves around 1.5KW of electricity needs for lighting in a house• In the winter we loose about 1.5KW of heating which came from those bulbs Royal Agricultural College
  20. 20. The law of unintended consequences• We are being encouraged and required by central governments to change heat producing lights bulbs for lower energy replacements.• This saves around 1.5KW of electricity needs for lighting in a house• In the winter we loose about 1.5KW of heating which came from those bulbs• In the winter we are all turning our boilers up as a consequence, wiping out much of Royal Agricultural the intended energy saving. College
  21. 21. The basics of central heating• Fuel (chemical energy) is burned in one location to raise the temperature of a “heat transfer medium”.• The heat transfer medium is moved to a distant location where the heat is needed through a “heat distribution system”• At the distant location the heat transfer medium gives up its heat to Royal Agricultural the local environment. College
  22. 22. Energy sources• Overwhelmingly space heating energy sources are biological fuels – Oil, coal, natural gas – Bio mass, bio gas• When they burn, they are combined with oxygen to create water and carbon dioxide, releasing heat energy during this “exothermic reaction” Royal Agricultural College
  23. 23. Central heat source• The heat source is usually a boiler, where water is heated• It can be a heat exchanger where air is heated, but these are less efficient and little used unless there is a need for mechanical ventilation.• Size of boiler chosen after carrying out heat loss calculations and adding in predictable environmental heating inputs Royal Agricultural College
  24. 24. Heat transfer media• A transfer medium is a fluid which can move heat from source to destination• The desirable medium properties are – high thermal capacity (it can hold a lot of heat in a small volume) – Ease of control – Non-hazardous• Water is ideal in most situations• Steam is useful in large scale installations• Air is much less efficient due to its low Royal Agricultural thermal capacity College
  25. 25. Heat distribution system• Water: pipework, usually copper or stainless steel if it needs to be strong• Steam: high pressure, large diameter pipes with integral insulation• Air: large ducts with minimum number of corners, interruptions or leaks Royal Agricultural College
  26. 26. Hot water pipework• Pipes should be insulated when they pass through unheated spaces: roof spaces, under ground floors• Pipes are not usually insulated where they pass through the heated part of the house, as the heat they radiate contributes to warming the house• Pipe work must be kept full, must be ventilated at high level and must Royal Agricultural have drainage taps at all low points College
  27. 27. Local heat emission• Where the heat is needed, the surface area of the pipework is maximised to emit as much heat as possible• This can be done through radiators, convector units or under floor pipe networks Royal Agricultural College
  28. 28. Radiators•Radiant heat and naturalconvection currents•Simple and largely fail safe Royal Agricultural College
  29. 29. Convector units•Air is blown over hot water pipes by a fan.•Very hot water can be used, which is efficient•Can be combined with ventilation using outside air intake. Royal Agricultural•Can be served by chilled water pipes from an air conditioning unit College•Noisy but very good where intermittent use is needed
  30. 30. Under floor heating • Entire floor is a radiator • Expensive to install • Efficient in areas where constant heating is needed, • Inefficient for intermittent heating • Insulation must be placed below hot pipes Royal Agricultural College
  31. 31. System control• Electronic control systems have increased the efficiency of heating systems more than any other technology• Time switches on boilers• Thermostats for radiators in rooms• Zoning of buildings with separate controls for each zone• Remote control via mobile phones/internet Royal Agricultural College
  32. 32. District heating• Central district boiler• Steam pumped to individual buildings• Heat exchangers in each building heats water for radiators in the building• Can be highly efficient in urban locations for large developments Royal• Loss of personal control Agricultural College
  33. 33. Professional advice• Space heating systems are amongst the biggest consumers of fossil fuels and biggest contributors to green house gas (CO2) emissions nationally• The design of any new building should aim to reduce the need for space heating to a minimum• In all but the simplest installations, the systems should be designed by a qualified services engineer to minimise their Royal environmental impact Agricultural College

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