28386348 HVAC Handbook Cooling in Commercial Buildings

7/31/2019 28386348 HVAC Handbook Cooling in Commercial Buildings

1/61

Laura Mansel-ThomasLaura Mansel-Thomas

Cooling in Commercial Buildings

Ar51 : Low energy architecture


2/61


Calculating Cooling Loads

During warm sunny periods, buildings with windows facing in asoutherly direction any aspect from east to west, through south are subject to daily cyclic heat gains from solar radiation.

In addition, further gains arise from artificial lighting, occupants and

other sources. In designing a building, it is important to ensure that it will not

become uncomfortably hot during sunny periods i.e. that themaximum peak temperature should not frequently exceed, say, 27oC.

The CIBSE A Guide describes a technique which enables the peakenvironmental temperature to be assessed.

If the calculated peak temperature is predicted to be excessive andsteps cannot be taken to overcome the problem by modification of thebuilding design, the need for mechanical ventilation or airconditioning is evident.


3/61


The technique requires that the following are calculated insequence:

1. Mean heat gains from all sources2. Mean internal environmental temperature

3. Swing from mean-to-peak, in heat gains from all sources

4. Swing from mean-to-peak, in internal environmentaltemperature

5. Peak internal environmental temperature In order to do this, a significant amount of information is required

about the building under analysis:

1. Areas and construction details of internal and externalelements, in order to calculate U values and admittance values

2. Areas and aspect of all windows and details of blinds and/orshading

3. Any casual gains from electric lighting, predicted occupancyand other sources

4. Details of ventilation rate

5. Peak and mean outdoor temperatures


4/61


The CIBSE A Guide technique is the basis for many other methodsfor calculating cooling loads, including software such as CYMAP and

TAS and the CIBSE Energy Code. The objective of the CIBSE Energy Code is to enable the most efficient

air conditioning system to be adopted for a proposed building. TheCode does this by allowing the designer to compare the electrical andthermal power demands of various types of air conditioning. TheCode also allows the identification of features of both the system andthe building that may give rise to potentially high consumption ofenergy, indicating where beneficial changes might be made.

The CIBSE Energy Code cannot cover all combinations of airconditioning technology. It does not attempt to address systems thatmake use of thermal storage to reduce peak loads, and cannot deal

with devices such as solar panels or wind turbines. Manual calculations can be used to work through the code but the

use of a computer program is more common.


5/61


Degree Days

Degree days are a measure ofthe variation of outsidetemperature which enablesbuilding designers to determinehow the energy consumption ofa building is related to the

weather. When the temperaturemaintained inside a building ishigher than the temperatureoutside, any building willspontaneously lose heat, byconduction and air movement.

The rate of heat loss is directlyproportional to the temperaturedifference between the insideand the outside of the building.This temperature difference isseldom constant.

In this figure, the average outsidetemperature is 16oC, which is the same asthe inside temperature. However the

building will still need heating for half theday. Degree days allow for this; they are ameasure of how much and for how longthe outside temperature is below a controltemperature. In this example, for each daythe difference is 4oC for half a day, or 2

degree days.


6/61


Degree days normally appliedto buildings can be of two kinds.

Heating degree days,defined as the meannumber of degrees by whichthe outside temperature on

a given day is less than thebase temperature, totalledfor all the days in the period.

Cooling degree days,defined as the meannumber of degrees by whichthe outside temperature ona given day exceeds thebase temperature, totalledfor all the days in the period.

This figure shows the variation ofoutside temperature in Liverpool on16-17 January 1987. Externaltemperature is almost always cyclic,with a daily maximum and a dailyminimum.


7/61


The usual method forcalculating degree days is often

known as the British GasMethod. This uses simpleformulae to calculate the degreedays per day from the dailymaximum and minimumtemperatures.

This is shown in the adjacentfigure for both heating andcooling degree days.

The great advantage of basingcalculations on maximum andminimum temperatures is thatthese are easily measured.


8/61


The heating degree day tablesusually published are for a basetemperature of 15.5oC, which is

lower than the temperature abuilding would generally beheated to.

This is to reflect the fact that notall the heat in a building comesfrom the heating plant people,

lights and machines alsocontribute.

Cooling degree days are usedmuch less than their heatingequivalents. One of their

important applications is foroperators of air-conditionedbuildings. There is no generallyaccepted base temperature and15.5oC is commonly used.


9/61


Air Conditioning

a system which gives automaticcontrol, within predeterminedlimits of the environmentalconditions, by heating, cooling,humidification, dehumidification,cleaning and movement of air in

buildings The primary function of air

conditioning is cooling. Mostsystems also filter the air.

Temperatures in a room may

rise above comfortable limits(around 27oC) due to internalheat gains, high outsidetemperatures or, usually, both.

Larkin Building

by Frank LloydWright (1904)


10/61


Typical situations which could requireair conditioning

Rooms with large areas ofsouth facing glazing

Rooms with high levels ofequipment

Computer server rooms

Art galleries (lighting)

Theatre projection rooms

Call centres

Rooms with very highoccupancies

Theatres/cinemas

Call centres


11/61


Air Conditioning


12/61


Local systems

Equipment is located in theroom itself.

Split systems

Through-the-wall units

Usually very inefficient Common in hotel rooms &

domestic applications unitshave been used worldwide andare generally in a range ofrefrigeration capacities from

1.5kW to 9kW.

Larger units are available these are usually mountedagainst an external wall and areused for small shops etc.


13/61


Split system Air Conditioning unit

Basic low cost system frequentlyused in retail and small commercialapplications.

A condensing unit is located on theroof or mounted on an external wall.

The unit does not provide fresh airand supply and extract mechanicalventilation is desirable this alsodiscourages infiltration.

Uses CFC or HCFC Refrigerants

Can heat and cool


14/61


Central Plant System

Used where the supply airtemperature can be the samethroughout the building e.g. atheatre or supermarket.

Fresh air enters & is mixedwith recirculated air

The air is filtered

In winter the air is heated

In summer the air is cooled


15/61


Components of a Central Air System typical poor

energy efficiency.


16/61


COOLING TOWER

An evaporative device for rejectingheat from buildings. Exploits the

latent heat of evaporation principal tomaximise heat rejection for a givenfootprint. Needs copious air and aclear discharge. The main source ofthe Legionella bacteria. The mostcommon method of rejecting heatfrom large buildings.

LOAD

COOLING

TOWER

WATER COOLED CHILLER


17/61


AIR COOLED CHILLER - Refrigerant Based


18/61


Partially centralised air/water systems

One of the disadvantages of centralised air conditioning systems isthat the ducts needed to deliver heating or cooling to the spaces aremuch larger than if ventilation only were supplied to the space.

Partially centralised systems use reduced duct sizes because they

only deliver enough filtered and tempered air to the rooms to satisfythe ventilation requirements. The heating or cooling demand issatisfied using room based devices.

Typical room based devices are fan coil units, which are supplied withheated water and/or chilled water from boilers and chillers situated in

the plant room. Fan coil units are fitted with heating and cooling coils. The tempered

air is mixed with room air and passed over one of the coils,depending on whether heating or cooling isrequired.


19/61


Fan coil system

The most common type of air conditioning in new offices andrefurbishments. It allows a great degree of flexibility because eachfan coil unit can provide air at a different temperature.


20/61


FOUR-PIPE FAN COIL UNIT

SYSTEM

BOILER CHILLER


21/61


LOW ENERGYSYSTEMS


22/61


Chilled Ceilings Chilled ceilings are composed of

an array of purpose builtsuspended ceiling panels. Thepanels are of a standard size andgenerally made from perforatedaluminium sheet.

A coil of copper pipe is fixed, in

close contact, to the back of thepanel. When chilled water iscirculated through this pipe theceiling panel becomes cool. As aresult, any air coming intocontact with the ceiling will be

cooled and will descend into theroom.

The room occupants will also feelcooler because their bodies willradiate heat to the chilled ceiling.


23/61


CHILLED CEILING WITH OVERHEAD VENTILATION

Room temperature control achieved by varying the temperatureof the ceiling :

Limited capacity to absorb heat gains

Good comfort conditions

Humidity control of central air vital no opening windows!


24/61


25/61


26/61



27/61


Chilled beams Chilled beams can be passive or

active. Passive chilled beams have a chilled

surface formed into a linear finnedcoil, which is then surrounded by apressed steel casing and suspendedfrom the ceiling.

Warm air rises to the ceiling andenters the top of the beam, where it iscooled by contact with the cold coil.

The cool air descends into the roomthrough outlet slots on the undersideof the beam.


28/61


Active chilled beam

Active chilled beams incorporatetempered ventilation air suppliedthrough ducting in the beam itself.Tempered air leaves the supplyducting through slots or nozzles withsufficient velocity that it induces warm

room air into the beam and throughthe cooling coil reducing itstemperature.

The supply and chilled room air mixand enter the room via outlet slots onthe underside of the beam.


29/61


ACTIVE CHILLED BEAM

Room temperature control achieved by control of individual beams orgroups of beams:

Cooling capacity up to 100 W/m2

Integrated lighting an option beams may be fully recessed

Limited humidity control is possible high humidity is a problem!


30/61


Advantages of chilled ceilings andbeams

Chilled ceilings and beams are a low maintenance way of cooling aroom. There are no internal fans or filters that could break down orneed cleaning all maintenance is at the central plant area soaccess is not regularly required into the space served.

They are also an energy efficient method of cooling, due mainly tothe operating parameters of the system.

1. The low fan speed used to deliver air to the outlet diffusers hasa low energy requirement (energy used by a fan is proportionalto the cube of the fan speed).

2. They operate at relatively high chilled water flow temperature

meaning the chiller has to do less work than for, say, a fan coilsystem.

3. Higher operating temperatures allow the use of free cooling(see later).


31/61


MECHANICALVENTILATION


32/61


CONVENTIONAL OVERHEAD VENTILATION air is introduced at ceiling level and the resulting condition in the room is amixture of the room air and the fresh air.


33/61


34/61


Air is supplied at low temperature difference, at low level and at lowvelocity

Heat and contaminants are displaced upwards

Air is extracted at high level and ducted back to the heat recovery plant The total cooling requirement to achieve comfort is greatly reduced

Plant size is reduced and running costs are greatly reduced

Conventional Cooling Displacement Cooling


35/61



36/61



37/61



38/61



39/61


Indirect Evaporative (Adiabatic) Cooling

Adiabatic cooling uses the evaporation of water to cool the air being suppliedto the spaces served. The evaporation process takes place within the air

handling unit that supplies fresh air and extracts stale air.Mains cold water is sprayed into the extract air stream within the air handlingunit to cool the air stream down by as much as 10oC. In this process, thehumidity of the extract air stream increases towards 100%. The now cooledextract air stream passes over a heat exchanger that carries the fresh airsupply. This cools down the supply air without transferring moisture to it.

The main advantage of this form of cooling when compared to mechanicalrefrigeration is that instead of consuming a vast amount of electrical energy, itonly uses a modest amount of mains water; the running costs areconsequently much lower (around one twentieth of the cost per kWh). Thesecond advantage is that the initial capital cost is lower.The main disadvantage is that the lowest supply temperatures that can beachieved on a hot summer day are around 20oC compared to a typical figureof 12oC for refrigeration based cooling systems. This can work very well with adisplacement ventilation system.


40/61



41/61


Air Conditioning a warning

Air conditioning uses about16% of all the electricityconsumed in the USA.

On a hot summer afternoon,air conditioning is responsible

for about 43% of the US peakelectrical load, keeping 200power stations busy.

In 1982, the city of Houston,Texas paid $3,310 million for

cold air, more than the GNPof 42 African nations.


42/61


ATELIER TEN - BACKGROUND

Winner

Innovation of the YearBuilding Services Awards 2000

Runner UpUp + Coming Consultancy of the YearBuilding Services Awards 1999

Founded 1990

Turnover 1.9m in 2002

Projects in the UK and abroad across

all sectors from 200k to 250m.

Numerous School, FE and HE Projects

34 Staff in London Office, 4 in New

York

Consistent contributors to Industry

and Education in energy conservation

and IT.

Award winners in 2000 for Innovation

for Primary School Design


43/61


CANNONS CITY CLUB

with

Daryl Jackson International

Phased renovation of 6,500m2 of HealthClub whilst maintaining it operational.Included full systems replacement and theinstallation of a CHP system for heatingup to 25 tons of water a day for showers.


44/61


EXPERIENCE

SCHOOL PROJECTS

Essex Sustainable School, Notley

Thomas Coram Foundation, London

Haverstock School, Camden

Stowe School

Tulse Hill School, Lambeth

Ecole Maternelle, DAours, France

St Anthonys School, Hampstead

Durand Primary School

Caldecott Foundation, Kent


45/61


CANNONS CITY CLUB

with

Daryl Jackson International

Phased renovation of 6,500m2 of HealthClub whilst maintaining it operational.Included full systems replacement and theinstallation of a CHP system for heatingup to 25 tons of water a day for showers.


46/61


FEDERATION SQUARE, Melbourne

with

LAB Design Studio + Bates Smart

International Design Competition winningscheme for an A$300m Cultural Complex inthe Centre of Melbourne. Completed incollaboration with AHW Consultants.

Includes an 11,000m2 Labyrinth. Winner ofthe 2003 Sustainability Award of theCement and Concrete association in

Australia.


47/61


THE EARTH CENTRE, Doncaster

with

Feilden Clegg Architects

Galleries for the National Centre forEducation and Enlightenment in thefield of Environment and sustainability.

A Millennium Lottery project.

Includes the largest thermal labyrinthin Europe and a 500m2 PV Array


48/61


Keble College


49/61



50/61



51/61


Ground Source Heating & Cooling


52/61


53/61


Keble College heating section


54/61


Keble College ventilation section


55/61


Keble College drainage section


56/61


Keble College domestic servicessection


57/61


Ineos Headquarters


58/61



59/61



60/61



61/61

References

GeneralMitchells Environment and Services Peter Burberry

Building Services Handbook Hall & Greeno

Essential Building Services & Equipment Fred Hall

CIBSE Guides A,B and C

Institute of Plumbing Plumbers GuideAir Conditioning

CIBSE Building Energy code 2: Energy demands for air conditionedbuildings

Low Energy Building Services

Environmental Design Randall ThomasDegree Days

Fuel Efficiency Booklet 7 Dept of theEnvironment

Date post:	04-Apr-2018
Category:	Documents
Upload:	bharatonkar
View:	293 times
Download:	9 times

28386348 HVAC Handbook Cooling in Commercial Buildings

Documents