1. 5508BESG Services and Utilities Lecture 4
Heating Installations

2. Recommended Reading CIBSE KS8 “How to Design a Heating System”
CIBSE: 2011 “Domestic Heating Design Guide”
CIBSE Guide A : “Environmental Design”
BSRIA “Illustrated Guide to Mechanical Services”
BSRIA BG4/2011 “Underfloor Heating & Cooling“
HVCA “Central Heating Installation Specification.”

3. There’s a lot to consider!

4. Step by Step Overview of the Design Principles for Heating Systems

5. Step 1: Select Design Temperatures
Internal Design Temperature: Selected to:
Maintain comfort conditions for human occupation.
Maintain conditions for processes, keeping animals or storing goods & artefacts.
Prevent fabric damage / condensation in the property.
For domestic applications the following internal design temperatures are usually adopted:

6. Recommended
Winter Internal
Design Temperatures

7. External Design Temperature:
The lowest sustained temperature you would expect the heating system to be able to still maintain the selected internal design temperatures:
Usually recommended to be -3oC for domestic heating applications.
For other types of buildings this is selected by a risk assessment and varies with the geographical location. (see CIBSE Guide A or J)

9. STEP 2: Complete Building Thermal Analysis (Heat Loss Calculations)
Two Mechanisms:
Heat loss by conduction through solid structures, wall, floors, roof, windows etc. known as “Fabric Heat Loss.
Heat loss due to warm air leaving the space and being replaced by cold air, known as “Infiltration” or “Ventilation Heat Loss”.
The sum of these two is the total heat loss.

10. Fabric Heat Loss Rate of Fabric Heat Loss is given by:
Rate of Fabric Heat Loss (Watts) = U value x Area x (temp inside - temp outside )
Qf = U x A x t
Where
U = coefficient of thermal transmission for composite surface structures W/m2oC
A = Surface area of the structure.
t = Difference in temperature between the inside and outside design temperatures.
This calculation is repeated for each surface within a room where a temperature difference exists across its surfaces.

11. U Values Can be obtained by:
Calculation from first principles knowing the composition of the structure.
Standard tables of pre-calculated values for common structures.
Note: the calculation of U values for ground floors or window is more complex than for walls or roofs therefore standard tables tend to be used.

12. Ventilation Heat Loss Where:
Rate of Ventilation Heat Loss is given by:
Rate of Ventilation Heat Loss (Watts) = 0.33 x No of Air Changes per Hour x Volume of Room x (Temp inside - Temp outside )
Qv = N V t
Where:
N = Number of times in an hour that ventilation/infiltration will cause the total volume of air in the room to be replaced by fresh unheated outside air.

13. Empirical Values for Infiltration
Traditionally the following values would be typically used for heat loss calculation purposes usually for existing older property:
Taken from CIBSE Domestic Heating Design Guide
Mechanical extract fans can increase the peak above these values, whole house mechanical ventilation with heat recovery can reduce the effective heat loss by 50%

14. With new buildings, Part L requires tighter air permeability requirements, the following gives more accurate empirical values.
Taken From CIBSE Guide A 2006 Edition

15. Total Heat Loss for Room
Total Heat Loss for a room is given by;
Total Heat Loss Rate = Sum of Individual Fabric Loss + Ventilation Loss
Qtotal = Qf + Qv
Qtotal =  (U x A x t) + (0.33 N V t)
In practice either calculation sheets or computer programmes would be used.

16. Typical calculation sheet
Taken from CIBSE Domestic Heating Design Guide

17. Heating System Key Decisions
Centralised or local (de-centralised ) system.
Heat media and means of distribution
Type of Heat emitters
Type of heat source

18. Centralised or De-Centralised?
Centralised: Heat generated at a single central location and distributed to the various locations to be heated.
De-centralised: Heat generated at or close to the locations being heated with minimal heat distribution around the building. Usually requires multiple heat generating appliance and fuel/energy supplies.
Note: This lecture will focus on centralised systems.

19. Heat Distribution Media
Air
Water (Low, Medium or High Temperature Hot Water)
Steam
Low temperature hot water and Air are the media most commonly used in the UK.

21. Note: This lecture will concentrate on LTHW Heating Systems
Note: This lecture will concentrate on LTHW Heating Systems. Systems that use air as their distribution media are often integrated with a ventilation system to form a Heating and Ventilation (H&V) system. These will be dealt with in a future lecture.

22. Step 3: Selecting Heat Emitters
For domestic heating these are likely to be:
Radiators
Natural Convectors
Fan Convectors
Under Floor Heating
For non-domestic heating systems the list could include:
Radiant panels and strips
Unit heaters

23. Types of Radiator
1. Panel Radiators: Panels of mild steel pressed & then welded together, approx 80% of output is convection.
Comparatively cheap, readily available off the shelf, wide variety of sizes and outputs, don’t project too far into room.
Large area to output ratio, limited life expectancy (for budget makes).
Single panel Radiator
Single Panel Radiator with convector fins
Double Panel Radiator with a double row of convector fins
Double Panel Radiator with one row of convector fins

24. Types of Radiator
2. Low Surface Temperature (LST) Radiators: A panel radiator with all hot surfaces protected so that no exposed surface exceeds 43oC. Intended for rooms with “at risk” occupants, e.g. children, elderly, infirm etc.
Advantages / Disadvantages similar to panel radiators, plus, tend to be larger size and cleaning is more difficult than panel rads.

25. Types of Radiator
3. Sectional Radiators: Made from cast sections (traditionally cast iron although aluminium is also used) joined together to form a radiator of any length. Very much an “architectural” appearance.
Advantages: Robust, long life expectancy, appearance.
Disadvantages: Cost, weight, tend to be larger, slow responding.

26. Types of Radiator
4 . Towel Rails and Architectural Feature Radiators: Wide range of designer radiators and towel rails are available, intended to make a statement as well as provide heating.

27. Natural Convector
Can be wall mounted, skirting heating or trench heating. Almost 100% convection output. All tend to be fast responding but can harbour dust.
Traditional wall mounted are not common in domestic heating.
Skirting heating; spread heat evenly around perimeter of the room.
Trench Heating: tend to be used under windows and patio doors
Traditional wall mounted convector
Skirting heating and perimeter convector installed around perimeter of the room
Trench Heating, often under windows

28. Placing radiators and natural convectors

29. Fan Convectors
High heat output to size ratio, can be effective over a large room volume, fast responding. Need a power supply to run the fan, generate small amount of noise, and tend to harbour dust, (most have a filter which needs occasional cleaning ). Tend to be used in kitchens, home offices and other non-noise sensitive areas.
Varieties include :
Traditional wall mounted, Kick-space (under cupboards) and hi-level for mounting over doors
Kick-space under unit fan convector
High level over door fan convector
Wall Mounted, office type fan convector

30. Underfloor Heating
modern underfloor heating system consists of plastic pipe laid in circuits in a floor screed or below a timber floor system, through which low temperature hot water is passed. The hot water is circulated at a lower temperature than for other forms of heating, (typically 40 to 50oC) and provides even heat distribution across the whole installed area. With this type of arrangement, heat is typically emitted in the proportions of 40% convective and 60% radiation.
Suspended timber floor
Screeded floor with clipping system

31. Floating Floor System: Pre formed profile laid on top of insulated slab, pipework laid into profile grooves with screed or floor finish to cover the pipes

32. Each circuit originate and terminate from a manifold

33. Typical underfloor heating configuration , note the positions of the manifolds
Taken from CIBSE Domestic Heating Design Guide

34. Radiant Panels & Strips
Low temperature panels
Used in non-domestic situations. May be either: Low Temperature or High Temperature Low Temperature Used extensively in offices, hospitals etc where the heat emitter forms part of the suspended ceiling. Used in factories or warehouses with high void spaces.

35. High temperature panels
As the name suggests these emitters give out most of their heat by radiation. Radiation has the advantage of heating objects rather than air. Therefore they are useful in very large void spaces such as warehouses and workshops etc of heating the occupants without having to heat the air. Running these at high temperature (above 100oC) significantly increases their output

36. Unit Heaters
These are fundamentally large, high output fan convectors mounted at high level used for industrial applications.

37. Emitter Comparisons:
Extract from CIBSE KS8 How to Design A Heating System

39. Stage 4: Pipework Configurations
Vent Pipe
Isolating valves
Heat emitters
Feed & Expansion Pipe
Pump
Fundamental pipework arrangement with the main components
Flow pipe
Boiler
Return Pipe

40. Schematic arrangement for a “Y Plan” system with stored hot water using three port diverting valve.
Note: Both the feed and expansion cistern and the cold water storage cistern have been omitted for clarity.
Three port diverting valve with motor controlled by a cylinder thermostat and a room temperature thermostat will send water from the boiler to either the calorifier or the heating or both depending on their temperatures.
Boiler

41. Schematic arrangement for a “S Plan” system with stored hot water using three port diverting valve.
Note: Both the feed and expansion cistern and the cold water storage cistern have been omitted for clarity.
2 Two port zone valves, 1 with motor controlled by a cylinder thermostat and the other by a room temperature thermostat will send water from the boiler to either the calorifier or the heating or both depending on their temperatures.
Boiler

42. Schematic Arrangement for a underfloor heating system including stored hot water and radiators (optional) incorporating a three port mixing valve to reduce the temperature of the water flowing in the underfloor circuits.

43. Heat Sources Fossil Fuel Boilers Low Carbon Boilers and Heat Sources
Gas (Natural or LPG)
Oil
Electricity
Solid Fuel
Low Carbon Boilers and Heat Sources
Biomass
Ground Source Heat Pump
Air Source Heat Pump
Hybrid (Combined gas boiler and air source heat pump)
Combined Heat & Power (CHP)

44. Step 5: Boiler Types (Domestic)
Regular or Traditional Boiler
Features.
The system is open vented and filled from a small cistern.
Expansion water is accommodated in the cistern.
The cistern provides automatic “top-up” for loss of water.
The boiler provides hot water via a hot water storage cylinder .
Can be used in conjunction with solar hot water.
The pump and other controls are separate from the boiler.

45. System Boiler Features.
The heating system is a closed system with no open vent.
Expansion water is accommodated in an expansion vessel situated within the boiler casing.
There is no automatic “top-up” for water loss.
The boiler provides hot water via a hot water storage cylinder .
Can be used in conjunction with solar hot water.
The pump and some of the controls are accommodated within the boiler package.

46. Expansion Vessels:
A pressure vessel with two compartments separated by a neoprene diaphragm, the heating system water on one side of the diaphragm and air or nitrogen under pressure on the other. When the heating system is heated, the increase in water volume due to expansion deflects the diaphragm and compresses the air or nitrogen (causing a slight rise in pressure). When the system cools the volume of water decreases and the diaphragm returns to its original position

47. Combination (Combi) Boiler
Features.
The heating system is a closed system with no open vent.
Expansion water is accommodated in an expansion vessel situated within the boiler casing.
There is no automatic “top-up” for water loss.
The boiler provides hot water instantaneously on demand, there is no water storage.
Not usually used in conjunction with solar hot water
The pump and some of the controls are accommodated within the boiler package.
Modern Gas fired boilers can typically be approximately 90% efficient

48. Commercial Boilers
Commercial boilers are similar to domestic boilers but with a much larger heat output.. They can be a single large boiler, a bank of boilers or multiple small boilers (Modular boilers) operating as a single boiler variable output.

49. Biomass Heating
Biomass: Fuels derived from living or recently living organisms. Most of these are based on wood or wood products. These may be:
Bark
Brash & Arboriculture arising
Logs
Sawdust
Wood Chips
Wood Pellets

50. Biomass Boilers Log Burning Stoves Log Burning Boilers
Pellet and woodchip Boilers.

51. Biomass Comparisons Advantages Disadvantages Low Carbon Fuel
Low Cost Fuel
Eligible for Renewable Heat Incentive (RHI) payments.
Environmentally sustainable fuel
High Initial Capital Costs
Large space needed for boiler and fuel stores.
Fuel source and delivery required.
Higher maintenance requirements.
Not as suited for intermittent use.
Ethical issues over land usage.

52. Heat Pumps (the low carbon alternative to boilers)
Ground Source Heat Pump:
Based on a refrigeration circuit where low grade heat is taken from a large source (the earth) and used to provide high grade heat for the heating system. Electricity is used as the enabling energy to move the heat. Hence 1kw of electricity can provide up to 3 or 4 kw of heat

54. Air Source Heat Pump: Based on a refrigeration circuit where low grade heat is taken from the external air and used to provide high grade heat for the heating system. Electricity is used as the enabling energy to move the heat. Hence 1kw of electricity can provide up to 3.5 kW of heat

55. Combined Heat & Power (CHP)
Stirling Engine Micro CHP; Uses the heat from the boiler to generate electricity in a Stirling Engine.
Internal Combustion Engine CHP: uses gas in a engine to generate electricity and uses the by-product heat as the heating source.