5508BESG Services and Utilities - PowerPoint Presentation

5508BESGServices and Utilities Lecture 4 1 Heating Installations

Recommended Reading2 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 .”

There’s a lot to consider!3

Step by Step Overview of the Design Principles for Heating Systems4

Step 1: Select Design TemperaturesInternal 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: 5

6Recommended Winter Internal Design Temperatures

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 -3 oC 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) 7

8

STEP 2: Complete Building Thermal Analysis (Heat Loss Calculations) 9 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.

Fabric Heat LossRate 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 tWhere U = coefficient of thermal transmission for composite surface structures W/m2oCA = 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. 10

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.11

Ventilation Heat LossRate 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 = 0.33 N V tWhere: 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. 12

Empirical Values for InfiltrationTraditionally the following values would be typically used for heat loss calculation purposes usually for existing older property: Taken from CIBSE Domestic Heating Design Guide 13 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%

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

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

16Typical calculation sheet Taken from CIBSE Domestic Heating Design Guide

Heating System Key DecisionsCentralised or local (de-centralised ) system. Heat media and means of distributionType of Heat emittersType of heat source 17

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.18

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

20

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. 21

Step 3: Selecting Heat Emitters22 For domestic heating these are likely to be:RadiatorsNatural ConvectorsFan ConvectorsUnder Floor HeatingFor non-domestic heating systems the list could include: Radiant panels and stripsUnit heaters

Types of Radiator1. 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). 23 Single panel Radiator Single Panel Radiator with convector fins Double Panel Radiator with one row of convector fins Double Panel Radiator with a double 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 43 o C. 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 Skirting heating and perimeter convector installed around perimeter of the room Traditional wall mounted convector 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 50 o C) 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. Screeded floor with clipping system Suspended timber floor

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 manifoldsTaken from CIBSE Domestic Heating Design Guide

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

35 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 100 o C) significantly increases their output High temperature panels

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

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

38

Stage 4: Pipework Configurations39 Boiler Vent Pipe Feed & Expansion Pipe Pump Flow pipe Return Pipe Heat emitters Isolating valves Fundamental pipework arrangement with the main components

40 Boiler 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.

41 Boiler 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.

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.

Heat SourcesFossil Fuel Boilers Gas (Natural or LPG)OilElectricity Solid FuelLow Carbon Boilers and Heat SourcesBiomassGround Source Heat PumpAir Source Heat PumpHybrid (Combined gas boiler and air source heat pump) Combined Heat & Power (CHP) 43

Step 5: Boiler Types (Domestic)Regular or Traditional Boiler 44 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.

System Boiler45 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.

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 46

Combination (Combi) Boiler47 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

Commercial Boilers 48 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.

Biomass HeatingBiomass: Fuels derived from living or recently living organisms. Most of these are based on wood or wood products. These may be:BarkBrash & Arboriculture arising LogsSawdustWood ChipsWood Pellets 49

Biomass BoilersLog Burning StovesLog Burning BoilersPellet and woodchip Boilers. 50

Biomass Comparisons AdvantagesDisadvantagesLow Carbon Fuel Low Cost FuelEligible 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. 51

Heat Pumps (the low carbon alternative to boilers) 52 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

53

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 54

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. 55