XXXXXX XXXXXX XXXXXXXXX CIBSEs essential guide to environmental design explained, Part Two Thermal properties, plant sizing and natural ventilation are among the key areas covered in the latest edition of the environmental design guide. Tim Dwyer highlights the most notable changes in CIBSEs indispensible guide T he CIBSE guide to Environmental design has had a major upgrade for the first time in nine years, and large parts of the edition have been revised. This is the second of three articles that aim to provide an overview of the new Guide A. As with all key CIBSE publications, this Guide can be downloaded free of charge by CIBSE members from the CIBSE Knowledge Portal www.cibse.org/knowledge chapter 3 thermal properties of building structures This chapter has one of the lightest touches of the 2015 Guide A revision. Updates and corrections include the redefinition of the equation for radiative heat transfer when considering an air cavity thermal resistance, and a clarification of the thermal-bridging impact of metal wall ties that pass across an insulated cavity. A small amendment to the wording of the explanation that U values apply between the internal and external environments helps to ease the uncertainty about which temperatures to use for those who are inexperienced at determining heat flow through structures such as ground floors. The chapter has been brought closer to current building techniques, with the introduction of multi-layer foil insulation and reorganised tables of glazing U values. These now include data for triple-glazed windows, as well as listing an extended set of additional thermal resistances, such as blinds, curtains and secondary glazing. Since the 2006 Guide, the effect of thermal bridging has become increasingly significant as standards require more rigorous and realistic measures of thermal performance. This is reflected by the inclusion of a new section on thermal bypass and a expressed in air changes per hour. There is general confusion in the industry including in written standards and academia about the denotation of air infiltration and ventilation. This is an area in which the author has extensive experience, so it is no surprise that this is clarified early on. The concept of airtightness has been brought forward from the latter stages of the previous document, and the section rewrite of the coverage of linear thermal transmittance. The tables of typical building constructions maintain their historical interest, but with very few of the external structures having a place in modern buildings. About the author Lead author Brian Anderson has extensive experience in the assessment of thermal transmittance for real building elements, having managed and delivered key, UK government guides on the evaluation and application of U values. chapter 4 Ventilation and air infiltration This chapter has been extensively rewritten and reordered. The reorganised introduction explains that, while building ventilation and air exchange provide fresh air and dilute pollutants, they can account for half of a buildings primary energy use. The information, data and equations have been developed and reorganised to give a core understanding, with the expectation that the simple tools could, for example, be set up using a spreadsheet model. The scope has a subtle change, noting that the assessment of Breather membrane Vapour barrier Plywood sheathing insulation Brickwork Figure 1: Data, calculations and examples of Chapter 3 such as for the timber-frame wall construction shown have few changes compared with the 2006 edition [Source: CIBSE Guide A 2015 Fig 3.6] Cavity timber frame Mortar joints Plasterboard (Not to scale) ventilation is not only useful in terms of passive cooling, but also in the general maintenance of thermal comfort. A useful addition is the explanation of the two units of ventilation airflow rate and airchange rate. The former is a volumetric flow rate, such as litres per second, while airchange rate is typically has been rewritten. It has more extensive descriptions of relevant terminology such as air leakage index and air permeability, plus typical values that will be used to determine appropriate air tightness in buildings. There is a stronger emphasis on the role of ventilation to secure optimum air use of mechanical ventilation, there is a set of sketches (Figure 2) of generic mechanical systems, and a discussion of the pressures that drive airflow through buildings and their ventilation systems. The two main room air-supply systems are noted together, with a few lines of description followed by brief notes on distribution techniques. This provides a preamble to a new discussion on environmental design for energyefficient mechanical ventilation, which considers fan power and methods of control, as well as air-to-air heat recovery and commissioning and maintenance. The next section covers the fundamentals of natural and mixedmode ventilation, with a much stronger emphasis on the application of natural ventilation as a cost-effective solution. The principles have, of course, not changed since the 2006 edition stack and winddriven ventilation; however there is a new commentary, which includes reference to more recent research. Methods for estimating their infiltration and natural ventilation has not changed significantly, but has been restructured and updated. The brief section on airtightness testing in the 2006 edition has been partly rewritten, with the notable increase in the upper exhaust Heat recovery (alternative to recirculation) Filter Chiller Heater Humidifier/ dehumidifier Mixing Draw-through box arrangement (see CiBSe Guide B) Dampers recirculation system Control Silencer Fan extract fan extract grille air terminal unit (diffused) May be coupled to: Fan coil unit VaV system active chilled beam Figure 2: example of generic mechanical system schematics included in Chapter 4 [Source CIBSE Guide A 2015 Fig 4.3 based on BRECSU GPG 257] Guide A can be downloaded free of charge by CIBSE members from the Knowledge Portal at www.cibse.org/knowledge quality for occupant health and comfort, with new tables covering minimum ventilation rates for dwellings, offices and other buildings most of which have been acquired from various UK regulatory documents. The expanded explanation of indoor pollutants includes the classic concentration decay equation, which allows analysis of the dilution effect of outdoor air on contaminants in a room. By applying this equation, the chapter explains how an understanding of dilution ventilation may be used to establish the air quality in a space, as well as the effect of incoming contaminants in the outdoor air. Before the chapter goes on to consider the effect of ventilation on heat loss, there is a very brief discussion of filtration that refers the reader to more appropriate sources. Having defined the basic heat loss (or cooling) equation for ventilation, a new concept is introduced. This accounts for the limits in heat transfer between the ventilation air and internal fabric of the building, which can be used, for example, when evaluating cooling from outdoor ventilation. In future additions or online supporting notes this may benefit from a little more explanation and an illustration of the consequence of the moderated ventilation affect. This section closes with an example of how the reservoir of the bulk of the air in the building may maintain reasonable air quality, even at low rates of ventilation. There follows a section that provides expanded coverage of mechanical systems. After a brief rationale for the Design question risk of overheating Concept Dynamic thermal modelling CiBSe steady and admittance methods Detail Scheme Bre environmental design manual CiBSe steady and admittance methods Dynamic thermal modelling Dynamic thermal modelling Size of openings for natural ventilation rules of thumb CiBSe aM10 Computational fluid dynamics CiBSe aM10 Computational fluid dynamics CiBSe aM10 Computational fluid dynamics Figure 3: an example of possible routes from design query to detail investigation [Source: CIBSE Guide A 2015 Fig 5.2] chapter 5 thermal response, plant sizing and energy conservation This chapter has been written to satisfy the need for establishing loads in buildings and evaluating baseline performance for regulatory purposes, and to help designers meet more exacting standards than those required by the UKs national calculation methodology (NCM). ASHRAE Standard 90.1 is cited as one of those standards where the emphasis is on detailed modelling of the HVAC systems, as opposed to the NCM, which is really designed for compliance checks. Engineers have frequently raised concerns about using black box software when they have little knowledge of the calculation method and no way of verifying the implementation of the underlying theory. As with the previous edition, this chapter recommends the use of CIBSE TM33 Tests for software accreditation and verification for that validation process, but emphasises the limitations of those tests. The need for integrated quality management is stressed and there are minimum requirements for the technical content of software tools, and a overheating. It highlights the need for dialogue with the client to include lighting and indoor air quality (and implicitly noise), as well as the thermal analysis and predicted operative temperatures. Such an analysis particularly in buildings that are seen as being passively environmentally controlled is likely to require an understanding of the effects of airflow throughout the spaces. This edition includes a far more extensive section on airflow modelling, which considers different techniques and applications, and replaces the few paragraphs contained in the 2006 version. To illustrate that the calculations to be carried out at each design stage depend on the design question being answered, there is a new table (Figure 1); this provides an example hierarchy of methods and tools to navigate a route between specific design queries and detailed resolution. This is a welcome addition to guide the designer towards establishing their own path through the plethora of tools and methods outlined in this chapter. The six appendices to Chapter 5 included in the print edition in addition to the six that are available online are a treasure trove of information. Local plant sizing Central plant sizing energy demand renewables Part L compliance rules of thumb CiBSe steady and admittance methods rules of thumb CiBSe steady and admittance methods CiBSe steady and admittance methods SBeM CiBSe steady and admittance methods CiBSe steady and admittance methods SBeM Benchmarks London renewables toolkit SBeM Dynamic thermal Dynamic thermal Dynamic thermal modelling modelling modelling Dynamic thermal Dynamic thermal modelling modelling Dynamic thermal Dynamic thermal Dynamic thermal modelling modelling Dynamic thermal Dynamic thermal modelling modelling modelling Dynamic thermal Dynamic thermal Dynamic thermal modelling modelling Dynamic thermal Dynamic thermal modelling modelling modelling limit of building pressure differential from 50 Pa to 100 Pa. The appendices contain updated pressure coefficient data, as well as more extensive air-leakage characteristics for building elements. The final pages provide the retro BASIC code listing for ASHRAE Standard 90.1 is cited as one of those standards where the emphasis is on detailed modelling of the HVAC systems, as opposed to the NCM, which is designed for compliance checks suggested method for using these tools. The challenge of assessing overheating is discussed, and reference is made to more extensive coverage in CIBSE TM52 The limits of thermal comfort: avoiding overheating in European buildings; however, the largest proportion of this chapter is still on the analysis and evaluation (and mitigation) of summertime temperatures in buildings. The CIBSE Admittance Method is applied within this section, with a commentary that provides a much clearer understanding of the concepts and application. Boundaries between building and system become fuzzier as more sophisticated modelling and simulation tools enable integrated design, so there is now a section on HVAC system and thermal storage modelling. A new section, Calculation methods They include some of the key worked examples that were previously in the main chapter, as well as additional supporting descriptions, derivations and calculations. New areas include banded weather data and bin-method application; an extensive discussion on glass and glazing; and the algorithm that drives the excellent (free) passive design assessment (PDA) tool, used to make speedy early assessments of building thermal performance. There is a fresh clarity in these appendices and, along with the rest of the chapter, they deserve the attention of many in the industry who consider that they model buildings. About the author Michael Holmes MCIBSE work has been used extensively in CIBSE publications to model buildings in order to establish design loads and building performance. cJ l Next month: Tim Dwyer completes this series by highlighting the significant changes in the chapters considering internal heat gains, moisture transfer and condensation, and health issues. Martin Liddaments AIDA air-infiltration calculator, which can be morphed into modern programming environments. About the author Martin Liddament FCIBSE is chair of the CIBSE Natural Ventilation Group. for thermal design, introduces freshly composed sections, covering: Heating plant sizing, Cooling plant sizing, Summer temperatures in buildings and Building energy demand. Although they include much material from previous editions, these areas have been completely rewritten to provide clearer and more joined-up explanations of these interdependent computations. The CIBSE Admittance method has been retained, but it is noted that it is there for its educational value, and is suitable only for conventional building air conditioning loads and early-stage overheating risk assessment. This perhaps recognises that modelling tools are overtaking the practical application of this simple method (no matter how much it is enjoyed by academics). However, the explanations and the sometimes difficult-to-comprehend concepts that underpin this cyclic calculation method have been rewritten to provide a more considered description of how to understand and implement it. It is applied extensively in the latter sections of the chapter. Chapter 5 emphasises the need for an holistic approach when undertaking building thermal analysis and particularly when examining