Heating and Water Services Design in Buildings

Keith Moss, Keith J Moss

• Publisher: Routledge
• Year: 2013
• Print ISBN: 9780415291859
• eBook ISBN: 9781134435999
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

This book provides a thorough and practical coverage of design procedures, with numerous examples and case studies. The author has worked with open learning candidates of all ages as well with college students and university undergraduates.

Heat requirements of buildings in temperate climates

1

Nomenclature

A	surface area (m^2)
C	specific heat capacity (kJ/kgK)
d	design conditions
dt	temperature difference (K)
dtt	total temperature difference (K)
f r	thermal response factor
F1, F2	heat loss factors
F 3	plant ratio
H	thermal capacity (kJ/m^2)
K	radiator manufacturer’s constant
k	thermal conductivity (W m/m^2K)
L	thickness of a slab of material (m)
L/k	thermal resistance of the slab (m^2K/W)
M	mass flow rate (kg/s)
n	space heater index
H	operating plus preheat hours
N	number of air changes per hour
p	prevailing conditions
Q f	conductive heat loss through the external building fabric (W)
Q p	plant energy output (continuous heating) (W)
Q pb	boosted plant energy output (intermittent heating) (W)
Q t	total design heat loss = Qf + Qv(W)
Q v	heat loss due to the mass transfer of infiltrating outdoor air (W)
R	fraction of heat radiation
R a	thermal resistance of the air cavity (m^2K/W)
R b	thermal resistance of brick (m^2K/W)
R i	thermal resistance of insulation (m^2K/W)
R p	thermal resistance of plaster (m^2K/W)
R si	inside surface resistance (m^2K/W)
R so	outside surface resistance (m^2K/W)
R t	total thermal resistance (m^2K/W)
t a, tai	indoor air temperature (°C)
t b	balance temperature (° C)
t c	dry resultant, comfort temperature (°C)
t d	datum temperature (°C)
t ao	outdoor temperature (°C)
t f	flow temperature (° C)
t m	mean surface temperature (mean radiant temperature) (°C)
t r	return temperature (°C)
t x	temperature of the unheated space (°C)
U	thermal transmittance coefficient (W/m^2K)
V	volume (m^3)
VFR	volume flow rate (m^3/s)
Y	admittance (W/m^2K)
ρ	density (kg/m^3)
Σ	sum of
Cv	ventilation conductance (W/K)

1.1 Introduction

Heat flow into or out of a building is primarily dependent upon the prevailing indoor and outdoor temperatures. If both are at the same value, heat flow is zero, and the indoor and outdoor climates are in balance with no heating required.

During the heating season (autumn, winter and spring), when outdoor temperature can be low, the space heating system is used to raise the indoor temperature artificially to a comfortable level, resulting in heat losses through the building envelope to the outdoors. The rate of heat loss from the building depends upon:

• • the heat flow into or through the building structure, Q_f (in Watts);
• • the rate of infiltration of outdoor air, resulting in heat flow Q_v (in Watts) to the outdoors as the warmed air exfiltrates;
• • building shape and orientation;
• • geographical location and exposure.

A single storey building will have a greater heat loss than a multi-storey building of the same floor area since there is little or no heat loss through the upper floors. On the other hand, the upper floors of a multi-storey building are more exposed to the weather.

STRUCTURAL HEAT LOSS

This occurs as heat conduction at right angles to the surface, and is initially expressed as total thermal resistance R_t, where

The thermal transmittance coefficient, U = 1/R_t (W/m² K), is the rate of conductive heat flow through a composite structure (consisting of a number of slabs of material, which can include air cavities) per square metre of surface, and for one degree difference between the indoor and outdoor temperature.

It follows that structural heat loss from the exposed building envelope is given by

INFILTRATION

Consider Figure 1.1, which shows a section through a building. The prevailing wind infiltrates one side of the building, where the space heating appliances must be sized to ra...

Table of contents

• Front Cover
• Heating and Water Services Design in Buildings
• Essential reading from Spon Press
• Title
• Copyright
• Contents
• Preface
• Acknowledgements
• Introduction
• 1 Heat requirements of buildings in temperate climates
• 2 Low-temperature hot water heating systems
• 3 Pump and system
• 4 High-temperature hot water systems
• 5 Steam systems
• 6 Plant connections and controls
• 7 The application of probability and demand units in design
• 8 Hot and cold water supply systems utilizing the static head
• 9 Hot and cold water supply systems using booster pumps
• 10 Flues and draught
• 11 Combustion of fossil fuels
• 12 Electric heating
• 13 District and community heating
• Index