Energy Management and Operating Costs in Buildings

Keith Moss

• Publisher: Routledge
• Year: 2013
• eBook ISBN: 9781135815165
• Edition: 1
• Topic: Architecture
• Subtopic: Architecture Methods & Materials

Managing the consumption and conservation of energy in buildings must now become the concern of both building managers and occupants. The provision of lighting, hot water supply, communications, cooking, space heating and cooling accounts for 45 per cent of UK energy consumption.
Energy Management and Operating Costs in Buildings introduces the reader to the principles of managing and conserving energy consumpton in buildings people use for work or leisure. Energy consumption is considered for the provision of space heating, hot water, supply ventilation and air conditioning. The author introduces the use of standard performance indicators and energy consumption yardsticks, and discusses the use and application of degree days.

1
The economics of space heating plants

Nomenclature

A	area (m^2)
AEC	annual energy consumption (J, etc., kWh)
d	temperature rise due to indoor heat gains (K)
DD	Degree Day(s)
dt	design temperature difference (K)
e	exponent, e=2.7183
F1, F2	temperature ratios
fr	thermal response factor
HWS	Hot water supply
k	constant
MDD	maximum Degree Days
N	number of air changes/hour
Qg	indoor heat gains (kW)
Qp	plant energy output (kW)
S	number of days in the period under review
SDD	Standard Degree Day(s)
tai	indoor air temperature
t	ao outdoor air temperature
tb,	B base temperature in °C
tc	dry resultant temperature
tm	mean outdoor air temperature
tn	minimum daily outdoor temperature
tx	maximum daily outdoor temperature
U	thermal transmittance coefficient (W/m^2 K)
V	volume of space (m^3)
Y	thermal admittance (W/m^2 K)

1.1 Introduction

The use of primary fuels in industrialized countries has been the subject of national interest only since the oil crisis of the early 1970s. Much work has been done in the UK and elsewhere to reduce the consumption of energy derived from fossil fuels since that time, particularly in the manufacturing industries. Energy used in building services is estimated at 45 % of national primary energy consumption in the UK, of which space heating, hot water supply and auxiliary power is estimated at 32%.

The building services industry therefore has a mandate here to design systems which conserve energy, to provide accurate forecasts of energy consumption, to promote energy conservation, to undertake energy audits and to monitor and target the consumption and future use of energy in buildings.

Clearly the building services engineer may only be responsible for one or two of these tasks but he or she should be able to contribute to all of them in a professional manner if called upon to do so. Energy managers on the other hand have a responsibility for all of these tasks.

Technical innovation and breakthrough in recent years has meant that boiler plant and associated equipment is more efficient, bringing the benefits of lower consumption of primary energy and less harmful releases of the products of combustion into the atmosphere.

It is likely that as this trend continues, with the increasing public awareness of issues which have a direct bearing on the well-being of our Earth, more emphasis will need to be placed upon the design of space heating plants in the world’s temperate climates and hence upon costs in use. This is due also to the release of harmful products into the atmosphere during manufacturing processes as well as during the activities of building construction and as a result of living and working in the buildings we create for ourselves. It does now appear that controlling the release of carbon dioxide and pollutants may have a more significant impact on the building services industry than that resulting from the diminishing reserves of fossil fuel.

1.2 The economics

The economics of space heating plant should therefore be more relevant now than ever before. The economic evaluation of building engineering systems includes:

• capital costs;

• costs in use;

• life cycle costs;

• investment appraisal.

Investment appraisal is considered in Chapter 8.

Life cycle costs relate to the estimated life of plant and systems and to the following factors: reliability, maintainability and safety. The features given in Table 1.1 will influence the life cycle costs.

Table 1.1 Factors affecting life cycle costs

Investment for the replacement or refurbishment of plant and equipment may form part of the life cycle costs.

The life of the plant and equipment may be less than the life of the distribution pipework and radiators, for example. It may therefore be prudent to consider plant and equipment separately from distribution when accounting for replacement and refurbishment. See also Chapter 8.

Capital costs include:

• design fees;

• fees for supervising the installation of the services;

• material and labour costs of the installation;

• commissioning costs;

• costs for supplying the utilities of gas, water and electricity;

• builder’s work and attendance costs.

Costs in use (operational costs) include:

• fuel;

• auxiliary power for boilers, pumps, fans, temperature controls etc.;

• preventive maintenance;

• corrective maintenance;

• insurance.

On large sites the client may consider buying in the supervision, operation and maintenance of the entire space heating plant or plants together with the management of its operational costs under an outsourcing agreement referred to as Contract Energy Management. Purchase of new plant can also form part of an outsourcing agreement.

FUEL CONSUMPTION

The estimation for fuel consumption for space heating depends upon:

• plant energy output;

• seasonal efficiency of boiler plant and systems;

• duration of occupied period;

• mode of plant operation;

• thermal inertia of the building;

• internal heat sources;

• Degree Days appropriate to the season and the locality.

PLANT ENERGY OUTPUT Q_P.

This is calculated from the design heat loss for the building and is determined from the following formulae. (It is important to note here that in the calculation of weekly, monthly or annual fuel consumption, design heat loss is used. This is equivalent to plant energy output Q_p regardless of whether the plant in question operates continuously or intermittently.)
Thus:

where F₁ and F₂ are temperature ratios involving the indoor design comfort temperature t_c, the indoor environmental temperature t_ei and indoor air temperature t_ai.

The temperature ratios are dependent upon the proportions of radiant to convective heat emanating from the space heating appliances. They can be determined from data in the CIBSE Guide [1] or from formulae in another publication in the series [2]. Clearly the heat flow path resulting from a system of natural draught convectors will start at the indoor air point and proceed to the dry resultant, environmental and finally mean radiant point. In the case of a system of high temperature radiant strip or tube the resulting heat flow path commences at the mean radiant point. Thus the temperature ratios are affected by the type of heating system proposed for the building and in turn the building design heat loss is also affected. This matter is discussed at length in another publication in the series [2].

If, however, the building is thermally insulated to current standards and has low infiltration rates, which is to say that it is well sealed from ingress of outdoor air, design heat loss can be determined in the traditional manner from:

with only limited loss in accuracy.

SEASONAL EFFICIENCY OF BOILER PLANT AND SYSTEMS

Boiler manufacturers’ quote efficiencies of their products under test conditions at full load. The efficiency of modern boil...

Table of contents

• Cover
• Halftitle
• Title
• Copyright
• Contents
• Preface
• Acknowledgements
• Introduction
• 1. The economics of space heating plants
• 2. Estimating energy consumption—space heating
• 3. Intermittent space heating
• 4. Estimating the annual cost for the provision of hot water supply
• 5. Energy consumption for cooling loads
• 6. Performance indicators
• 7. Energy conservation strategies
• 8. Cost benefit analysis
• 9. Energy audits
• 10. Monitoring and targeting
• Appendix 1. Standard heating Degree Day data
• Appendix 2. Energy conservation measures
• Appendix 3. Preventive maintenance measures
• Appendix 4. Energy Efficiency Office’s series of booklets on Introduction to Energy Efficiency
• Appendix 5. Monitoring equipment
• Appendix 6. Cost benefit tables
• Appendix 7. Standard service illuminance for various activities/interiors
• Appendix 8. Source organizations and addresses
• Appendix 9. Source journals
• Appendix 10. Some current energy saving schemes
• Bibliography
• Index