The Passivhaus Planning Package (PHPP) is a design tool to help architects and Passivhaus Designers achieve the Passivhaus or near-Passivhaus ultra-low-energy standard. It takes the guesswork out of the design process by accurately predicting a proposed design’s energy performance.

Once a design has been set up in the PHPP, the Passivhaus Designer and architect can test out changes to see their effect on the building’s energy performance. This process, used iteratively, allows designers and clients to weigh up different options for trimming back the spec to the minimum needed for the desired energy standard, thereby avoid over-engineering. This can save thousands of pounds, particularly on high-cost items such as windows, even on the build of a single home.

The history and accuracy of the PHPP

The PHPP was first developed in 1998, drawing on experience modelling the first prototype Passivhaus in Darmstadt-Kranichstein in Germany, where the bespoke software models required the entry of thousands of pieces of information in order to get a working model of the design. The PHPP requires a lot less data to be entered but still models the design’s energy performance accurately. That said, compared with the Standard Assessment Procedure (SAP) energy assessment tool commonly used in the UK, the PHPP today still demands considerably more time to enter all the data needed to create a working model. However, this extra effort is worth it, because the PHPP has an excellent track record of accurate prediction – as illustrated in Figure 7.1 overleaf, which compares energy use predicted by the PHPP with the ‘real-world’ results for a range of occupied homes in Germany: a typical ‘low-energy’ development and three Passivhaus developments. The PHPP models energy use with an assumed internal temperature of 20°C. In an estate or ‘settlement’ of similar houses, different occupants will have their own ideas of what constitutes a comfortable temperature.

PHPP – science versus art?

Some have expressed the view that the PHPP can influence the design process to its detriment, by cramping the artistic or creative inspiration needed to realise genuinely uplifting architecture. As has been discussed, most build projects are subject to multiple constraints, many of which can or do hinder the creative process. In recent years, energy performance has been added to this list of constraints. By enabling experimentation with different design options, the PHPP lets the designer see the effect of those options on energy performance. In the hands of a creative architect, those options should help to stimulate new ideas rather than close ideas off.

The Passivhaus approach is pushing higher performance, and there are many other fields of design where very specific performance criteria must be met – in particular laptop computers, for example, where performance and ergonomics are matched with aesthetics to make highly desirable products (this is part of the success of Apple). There is no inherent conflict between performance and design here: in fact, many would argue that there is an interconnectivity between them – limits drive better solutions.

PHPP software

Version 7 of the PHPP, which was released in summer 2012, consists of three spreadsheets and a 217-page supporting manual. The main spreadsheet is complex, consisting of 36 interlinked worksheets. A ‘Final Protocol’ supplementary spreadsheet is provided to help with design and commissioning of the heat recovery ventilation system (MVHR), and there is an import/export tool (new in Version 7) that allows the PHPP to link to CAD (computer-aided design) applications. The spreadsheets are designed to run on Microsoft Excel but (although not formally tested) can also be run on Open Office’s spreadsheet program. The Passivhaus Institut chose to use the more open format of a spreadsheet rather than develop bespoke software partly because of cost limitations, but also because it is keen to allow users of the PHPP to see how the calculations are derived.

Figure 7.1 Comparison of actual energy performance with that predicted by the PHPP.
Source: Passivhaus Institut

The PHPP can be bought direct from the Passivhaus Institut (www.passiv.de) or (in the UK) from the AECB (www.aecb.net/carbonlite/phpp.php) at a similar price, around £150 (much cheaper than SAP).

The PHPP worksheets

The description in this chapter is not intended to be comprehensive or be a replacement for formal training in using the PHPP, but it highlights the key parts of the model that need to be completed before it starts to produce meaningful information. The screenshots shown here were taken from the previous version of the PHPP; however, the worksheets in Version 7 mostly look very similar. Version 7 also has additional features, including support for a broader range of climates and support for the EnerPHit standard.

The cells in the worksheets are colour-coded to indicate which are for entering data (yellow); which are calculated, show default values, or reference other sheets (white); and which are calculated and display important results (green).

Verification

The main purpose of the Verification worksheet is to summarise key results of the model. It starts to show meaningful information only when the other important worksheets (described in the following pages) are complete.

Part of the screenshot shown in Figure 7.2 overleaf includes a table called ‘Specific Demands with Reference to the Treated Floor Area’; this shows whether the Passivhaus standards are being met. The model assumes an interior temperature of 20°C, and this figure isn’t normally changed. However, it is interesting to watch the effect on the building’s energy performance of entering a lower or higher internal temperature.

The model has two modes – ‘Verification’ and ‘Design’. In Verification mode, for residential buildings the model calculates the number of occupants by dividing the treated floor area (TFA) by 35m² (the assumed floor area per occupant). In Design mode, if the planned number of occupants is entered, the model uses this figure rather than the derived Verification figure to calculate internal heat gains. In a large house with few occupants, you would use Design mode to check that the ventilation unit is appropriately sized.

Figure 7.2 Screenshot of the PHPP Verification worksheet.

Areas

Dimensions of all building elements, except the windows, are entered in this worksheet. The information tells the PHPP the external area of the thermal envelope: walls, floor and roof. The use of external dimensions for this calculation in the PHPP is different from the current UK convention, but there is a good, practical reason for this approach, as we will see in the next chapter.

Common mistakes

Note that it is important to ensure that for each line entered in the Area Input section of the worksheet, the correct Group number, e.g. ‘Floor slab / basement ceiling’ or ‘Treated floor area’ (Column D) and ‘Building element assembly’ (Columns T and U) have been selected. Each Building Element Assembly is defined according to the data entered in the U-Values worksheet (see opposite).

Treated floor area (TFA)

As observed in Chapters 1 and 5, Passivhaus uses a stricter definition of what constitutes usable floor area, known as treated floor area (TFA), than that normally applied in the UK. It is very important not to overestimate the TFA in the PHPP, as to do so will result in the PHPP giving over-optimistic figures for the building’s energy performance. In summary, the TFA excludes any floor area taken up by:

•  external and internal walls

•  chimneys and columns with a floor footprint over 0.1m² and over 1.5m high

•  stairs with more than three steps

•  plant rooms (e.g. hot water storage cupboard), unless plant equipment is wall-mounted, in which case 60 per cent of the floor area of the room can be included. A utility room may or may not be excluded, depending on what plant equipment is in it

•  basements, unless within the thermal envelope and without windows, in which case 60 per cent of the floor area can be included

•  unheated conservatories (because they are outside the thermal envelope).

It does include:

•  floor area within the thermal envelope (i.e. not terraces, balconies, etc.)

•  window reveals that are more than 0.13m deep, where the window goes down to the floor

•  floor area taken up by fitted shower trays, cupboards and other built-in furniture.

Any floor area where the ceiling height is 1-2m is counted, but only at 50 per cent of the full area; where the ceiling height falls below 1m, the floor area cannot be included in the TFA.

Thermal bridges

The Areas worksheet is also used to enter the length and psi-value of any thermal bridges in the design. In a Passivhaus, the aim is to design out all thermal bridges, but this is not always feasible, especially in retrofits. Where it is not possible, the additional heat losses caused by the thermal bridges need to be entered into the PHPP, to ensure the model remains accurate. The PHPP does not calculate the thermal bridges automatically; this has to be done separately, with the results entered into the worksheet. Chapter 8 looks at thermal bridges and psi-values in more detail.

U-Values

This worksheet calculates the U-value for all building elements except the windows. After you start entering data into the U-Values worksheet, a summary of the U-values is displayed in the U-List worksheet.

In the example pictured below and represented in Figure 7.3 overleaf, an exterior wall built from I-beam and cellulose insulation and a wooden rain screen is described from outside to inside. The rain screen itself is not included in the wall make-up, but does marginally affect the exterior surface resistance (R_se – see overleaf). The I-beam is described in Area sections 2 and 3 as percentages of the wall, seen laterally, that are different from the material in Area section 1. Although this method of using percentages is a bit clunky (until you get used to it), it allows the PHPP to model walls with discrete timber structural elements that would otherwise not be possible to model. Where a material used within an external building element has a much higher conductivity (more than four or five times) than the surrounding insulation, the PHPP is not able to model the U-value accurately and additional thermal bridge calculations need to be made.

I-beam wall under construction, represented in the U-Values worksheet example shown overleaf.

Two pieces of information are needed for each material within the building element: its thickness (in mm) and its thermal conductivity or lambda value (in W/mK). This value (also known as the k-value) is usually provided by the material’s manufacturer; however, the manufacturer’s quoted lambda value cannot be taken as read, unless accompanied by a CE mark, which normally signifies that the conductivity has been determined according to the relevant European Standard (EN) – in this case derived according the Lambda 90/90 convention – see box, right. Without a valid CE mark, a Passivhaus Certifier will require uplift, as much as 20 per cent, in the lambda value. See Appendix B (Thermal conductivity values) for lambda values of some common materials.

Figure 7.3 Screenshot of the PHPP U-Values worksheet, containing data for the I-beam wall pictured on the previous page.

The thermal resistivity (the material’s ability to resist the passage of heat) of the interior surface (R_si) and exterior surface (R_se) of the building element also need to be entered. In poorly insulated structures, the surface resistivity has an effect on U-values. In ultra-low-energy buildings, even though the U-value is less sensitive to these figures, it is still important to enter R_si and R_se values in order to get an accurate U-value.

Common mistakes

It is very tempting to use a manufacturer’s quoted lambda value, especially if the design’s annual space heat demand is close to or above the 15kWh/m².a limit. But it is important to be conservative in using lambda values, applying the 20-per-cent uplift rule where there is no CE mark.

Ground

The Ground worksheet measures heat losses through the base of the building. If no data is entered into the worksheet, the PHPP will make standard assumptions about these losses, which will be valid for many UK buildings.

WinType

This worksheet contains some technical information that is more fully explained in Chapter 11. As we see in that chapter, windows are a critical element in a Passivhaus or any ultra-low-energy building, and this is reflected in the PHPP. Because of the way the PHPP works, it is more practical to complete the WinType worksheet before the Windows worksheet (see page 100). The WinType worksheet is divided into two halves. In the first, information is entered about the glazing units; in the second, information is entered about the window frames. Figure 7.4 overleaf shows the two sections of the worksheet.

Both sections give values for some standard and generic window glazing and frame types, as well as for examples of Passivhaus-certified components. The rows in yellow at the beginning of each section allow Passivhaus Designers/ Consultants to enter details of the windows they are planning to use if these are not listed.

All the information entered into this worksheet and the Windows worksheet allows the PHPP to generate a whole-window U-value (Uw) and an installed whole-window U-value (Uw, installed) for each window. This contrasts with the whole-window U-value quoted by manufacturers, which is based on a window of standard size and configuration (see box on page 172, Chapter 11). Window manufacturers often seem reluctant or unable to provide all the energy performance information needed for the WinType worksheet. However, manufacturers of Passivhaus-suitable and Passivhaus-certified windows should be able to do so.

Glazing information

Two pieces of information are needed:

•  g-value – measure of the percentage of energy from the sun that passes through the glazed unit to the inside. The g-value is normally expressed as a fraction between 0 and 1.

•  Ug-value – the U-value of the glazed unit (as distinct from the whole window), taken through the centre of the pane, measured in W/m²K.

g-values

The g-value is one of the critical factors in determining the amount of solar gain window glazing of any given size will deliver. In a cool-temperate climate, where winter solar gain is desirable, windows on any building façades that are subject to solar gain should have a g-value of above 0.5; ideally 0.6 or more. In a hot climate, where cooling load is more of an issue than heating load, lower g-values, below 0.35, are preferable. Table 7.1 on page 99 shows typical g-values for different types of glazed units.

Ug-values

A Passivhaus-certified window requires a Ug of less than 0.75W/m²K, for a vertically inclined window (i.e. not a roof light) in a cool-temperate climate¹ such as the UK’s, and a triple-glazed, argon-filled unit with two 14mm or bigger spacers will comfortably achieve this. Ug requirements for inclined and horizontally mounted roof lights are a little less strict: 1.00 and 1.10W/m²K respectively. See Chapter 11 (pages 170-6) for more information on window U-values.

Frame information

The characteristics of window frames have a considerable impact on the overall performance of the window. The pieces of information required in the PHPP are:

•  U_f-value – the U-value of the frame (measured in W/m²K).

•  Width of each frame (top, left, right, bottom), measured in metres.

•  Psi-value (ψ) of the spacer (ψ_spacer).

•  Psi-value (ψ) of the junction where the frame meets the wall (ψ_installation).

Frame U-value (Uf-value)

While manufacturers find it relatively easy to make triple-glazed units with a low enough Ug-value for a Passivhaus, to date the frames have been more challenging. A Passivhaus-certified window should have a U_f-value of below 0.80W/m²K. A few manufacturers have achieved this, but many have not. Either way, it is good practice to specify windows where the frames comprise not too high a percentage of the total window area. Even at a U-value of 0.80, windows perform poorly relative to walls in an ultra-low-energy home. Whereas the glazed area performs the key functions of providing day-light and allowing in solar energy, the frames, of course, do neither.

Figure 7.4 Screenshot of the two parts of the WinType worksheet.

Psi-value of spacer

Like the frame, the spacer is an energy-performance weak point in windows, and its psi-value has a significant impact on the window’s the overall performance. ‘Warm-edge’ or insulated spacers have psi-values below 0.05W/mK; the best ones below 0.03W/mK.

Psi-value of frame–wall junction

The installation psi-value (frame–wall junction) is also a significant determiner of the installed window’s overall performance. In the PHPP, the designer should assume an installation psi-value of 0.04W/mK, unless separate thermal bridge modelling can demonstrate a lower value. Chapter 11 covers the principles of how to detail window–wall junctions to minimise thermal bridging and air leakage.

Table 7.1 Typical g-values for different glazed unit types

* If the Ug value is below 0.75W/m²K.

^† But can be used in Passivhaus buildings in warmer climates.²

Common problems

The window technical data described above has a surprisingly large impact on the building’s performance. Getting accurate figures from the window manufacturer is therefore very important. Manufacturers who fabricate windows for Passivhaus buildings should be able to provide this data. However, in a project where the design is to a less demanding fabric energy standard, such as the Code for Sustainable Homes (CSH) or the AECB Silver Standard, poorer-performing windows can be used, in which case it is likely that there will be no frame U-value (Uf) or spacer psi-value (ψ_spacer) available. These values could be individually calculated in THERM (see Chapter 8); otherwise very conservative values would need to be entered.

Windows

The Windows worksheet is used to compile information about each window in the building. Most of this can be taken directly from the building’s window schedule (a list of all the windows in a building), except when a window consists of multiple casements, in which case each casement must be entered as a separate window. The following information needs to be entered for each window:

•  A short description of the window (usually taken from the window schedule).

•  Deviation from north – tells the PHPP what direction the window faces.

•  Angle of inclination from horizontal – normally 90°, except for roof lights.

•  Width and height of the structural or ‘rough’ opening. If the window is round, enter dimensions for a square of equivalent area. This will give a more conservative result, as a square window will have more frame than a round or oval one of equal area.

•  A façade into which the window is being installed (the façades are defined in the Areas worksheet).

•  The window’s glazing (choose a glazing type that has been defined in the WinType worksheet).

•  The window’s frame (choose a frame type that has been defined in the WinType worksheet).

•  Installation – for each window side, enter ‘1’ where a window side is adjacent to a wall or ‘0’ where it is adjacent to another window. This determines whether or not the heat losses due to the installation thermal bridge are applied. Where a window is partly bounded by another window and partly by a wall, enter a fraction to reflect this.

Mullions

There is also a facility in this worksheet to describe windows with mullions. However, as frames (and mullions) and the spacers that they necessitate are energy-performance weak points in a window, specifying windows subdivided into mullions will significantly increase their heat losses and decrease the solar energy captured through the glazing. This is an instance where Passivhaus can discourage certain designs on costs grounds (though not necessarily rule them out). Currently, Passivhaus-suitable windows are mostly made on the Continent or copy Continental window styles, where mullions are uncommon in new builds. As window manufacturers in each country start to respond to growing demand for ultra-low-energy windows, they will design ones that reflect domestic architectural styles. Windows with mullions will always carry an energy-performance penalty, but this does not mean they cannot be used in a Passivhaus, except perhaps in extremely cold climates.

The left and right (and centre) sections of mullioned windows need to be entered in the WinType worksheet as separate window types (see page 97), owing to the different frame widths in each mullioned section.

Curved windows

If the design includes a curved window as part of a curved façade, enter the ‘deviation from north’ (direction of the window) of the lateral midpoint of the window and measure the dimensions as if it were flat, as shown in Figure 7.5 below.

Southern hemisphere

If the PHPP model is for a building in the southern hemisphere, the window ‘deviation from north’ figures need to be inverted. For example, if the property being modelled is in Australia, and has a north-facing window, the ‘deviation from north’ should be entered as ‘180’, not ‘0’ as would be the case if it was in the northern hemisphere.

Common mistakes

Unless the design is for a house on a straight north–south or east–west axis, it can be quite easy to enter the wrong information in the ‘deviation from north’ column. Likewise, you should double-check the ‘window rough openings’. It is also easy to overlook the need to enter each section of a mullioned window as a separate entry.

Shading

As noted in earlier chapters, shading is important in Passivhaus and ultra-low-energy building design. Winter shading will reduce desirable solar gain and add to the building’s heating requirements and is therefore to be minimised where possible. Summer shading produces unwanted solar gain, resulting in a greater risk of overheating. The Shading worksheet deals only with winter shading. It picks up information that has been entered into the WinType and Windows worksheets, then calculates the glazed area based on the window opening sizes and frame dimensions provided in the Windows and WinType worksheets respectively. Shading information needs to be added for each window. The information required in this worksheet is as follows (all items, except the last one, are measured in metres).

Figure 7.5 Describing the direction and width of a curved window in the PHPP.

•  Height of shading object (h_hori) – taken from the top of the shading object to the base of the glazed area of the window being shaded (see Figure 7.6 below).

•  Horizontal distance to shading object (d_hori) – taken from the top of the shading object to the external glazed surface (see Figure 7.6 below).

•  Window reveal depth (o_reveal) – the distance between the external surface of the glazing and the external surface of the wall (see Figure 7.7 opposite).

•  Distance from glazing edge to wall reveal (d_reveal) – in a window without mullions, this is a simple figure. In a mullioned window, it is a bit more cumbersome: the average (arithmetic mean) of the two dreveal figures must be taken. In the example in Figure 7.7, the average (mean) of d(left)_reveal and d(right)_reveal would be entered into the PHPP. In a window with many mullions, this calculation would need to be repeated for each mullioned section – rather time-consuming!

•  Overhang depth (o_over – see Figure 7.8 opposite).

•  Distance from upper glazing edge to overhang (d_over – see Figure 7.8).

Additional shading reduction factor (r_other) – this is entered as a percentage, where (rather counter-intuitively) 100% means no additional shading and 0% means total shading. If it is left blank, the PHPP assumes that there is no additional shading. You should enter a figure only if there is a tree or some similar object that partly shades the window. A useful visual representation of any additional shading can be gained by loading the architectural site and building plans into Google SketchUp (www.sketchup.com) or similar and setting the site’s longitude and latitude; this facilitates a more accurate estimate of the shading percentage.

Figure 7.6 h_hori and d_hori in the Shading worksheet.

Figure 7.7 d_reveal and o_reveal in the Shading worksheet.

Figure 7.8 o_over and d_over in the Shading worksheet.

Ventilation

The Ventilation worksheet is divided into two parts. The first, shown in Figure 7.9 below, is used to compile information to determine the size of the ventilation system required. In a Passivhaus, the MVHR system supplies fresh air to living and sleeping areas, and extracts stale air from ‘wet-room’ areas (kitchens, bathrooms and WCs). It also recovers heat from the extracted air when needed (during cold weather) and supplies it to the new air. The number of kitchens, bathrooms, showers and WCs is entered into the worksheet, and an airflow rate of 30m³/hr per person is recommended and is assumed by default, as are recommended extraction rates for different extraction points. The number of air extraction points may need to be changed or entered. The PHPP calculates an average airflow rate from this information.

(The supplementary Final Protocol spreadsheet, provided with the PHPP, allows you to design the MVHR system in more detail. Figures from this spreadsheet need to be entered manually into the Ventilation worksheet of the PHPP. The Final Protocol spreadsheet can also be used to commission an MHVR unit.)

Next, two ‘wind coefficient’ factors should be entered to describe the degree to which the building is protected from wind. In this case, approximate data is adequate for the purposes of the PHPP. Below this there is a box to enter the measured air change rate through the building fabric, taken from the building’s first or most recent airtightness test, during which the building is pressurised and depressurised by 50Pa (pascals) above and below ambient atmospheric pressure (see Chapter 9). The PHPP assumes the maximum allowable Passivhaus airtightness value of 0.6ach until the results of the air test are entered.

Figure 7.9 Screenshot of the system sizing information in the Ventilation worksheet.

The section of the Ventilation worksheet below this (see Figure 7.10 below) is used to describe the MVHR system. First, indicate whether the MVHR unit is to be located inside or outside the thermal envelope. Second, select the MVHR unit using the drop-down box. If the unit to be used is not in the list, add one in the ‘User defined’ section. Less common than a standard MVHR unit, a compact unit may be used (this combines MVHR, hot water and heating in a single ‘box’). Its MVHR specification will be displayed automatically in the Ventilation worksheet once the unit’s details have been entered into the PHPP’s Compact worksheet. Compact units are likely to become more popular in coming years, as more achieve Passivhaus-certified status. Their chief benefit is space saving – which is an important consideration.

Figure 7.10 Entering information on the MVHR unit and the ducting between the unit and the thermal envelope in the Ventilation worksheet.

Requirements for a Passivhaus heat recovery (MVHR) unit

As we saw in Chapter 3, the MVHR unit is one component of a Passivhaus that should be certified if the building is to meet the Passivhaus standard. The worksheet requires six values for the MVHR unit, as shown in Table 7.2 below, along with the criteria that these must meet for a Certified Passivhaus MVHR unit.

The lengths and psi-values of the sections of ducting between the MVHR unit and the boundary of the thermal envelope also need to be entered. These are critical to the efficiency of the MVHR system as a whole. If the MVHR unit is located within the thermal envelope, these ducts are the intake (or ‘ambient’) and exhaust ducts carrying cold air. If the MVHR is located outside the thermal envelope, these ducts are the length of supply and extract ducts carrying warm air between the MVHR and the boundary of the thermal envelope (see Chapter 12, page 200). The psi-values of the ducts have to be calculated in a pair of ‘Secondary Calculation’ boxes. For each of these secondary calculations, the following information is needed:

•  Diameter of the duct (in mm) – in a single residential dwelling this is normally 160-180mm.

•  Thickness of the insulation (in mm) – minimum 50mm.

•  Whether the external surface is covered in reflective material.

•  The conductivity (lambda value) of the insulation around the duct.

The insulation material must be impervious to water, so a material such as Armaflex^® needs to be used. As is discussed in Chapter 12, the ducts between the MVHR unit and the thermal envelope should be kept as short as possible. If they are overly long or inadequately insulated, this will have a significant effect on the building’s annual heat demand. Tweaking these variables in the PHPP illustrates this point well.

Table 7.2 MVHR values

^* As determined independently using Passivhaus Institut methodology

^† ‘A-weighted’ decibels

Annual Heating Demand

As the other key worksheets are completed, this worksheet starts to provide a useful summary of the building’s heat losses and gains. The assumed (default) room height of 2.5m (Vv) can be changed.

Summer

The Summer worksheet calculates the percentage of summertime overheating. The Passivhaus standard includes a limit (10 per cent) on the number of hours per year when the internal temperature exceeds 25°C. Some of the building-specific factors that affect this, and need to be entered or checked (i.e. are the default values correct for your build?), are given below.

•  Specific heat capacity – this is a measure of the building’s thermal mass. There are three suggested values (60, 132 and 204Wh/K per m² of treated floor area [TFA]) – another example of where the PHPP requires only an approximate value in order to model the building’s performance accurately. The default value is 60, which assumes a low thermal mass.

•  Overheating limit: 25°C by default, in line with the Passivhaus standard. It is possible to change this value in order to get a broader view of the extent of overheating, which is useful.

•  Air change rate from natural ventilation and/or mechanical ventilation.

•  Additional summer ventilation for cooling – indicate whether this is to be achieved by manual opening of windows at night-time or by an automated system.

The resulting frequency of overheating percentage is then displayed. Whether 10 per cent overheating, although allowed, is acceptable is for you to decide. We suggest a much lower figure, especially in view of uncertain future climate patterns.

Shading-S

The Shading-S worksheet picks up data from the Windows and Shading worksheet and provides two extra columns to indicate what additional shading is provided in summer. The temporary shading reduction factor (z) describes shading from blinds, awnings or other shading devices. As with the entry of the additional shading reduction factor (r_other) in the Shading worksheet, using Google Sketchup helps to make a more accurate estimate of the percentage shading. Where the shading device will be operated manually, the PHPP convention is to apply a factor (70 per cent) to model the assumption that we don’t always remember to operate the shade during hot weather. Shading is based on external devices, as this is the only truly effective shading option; you can enter values for internal shading devices, but these will have a much more limited effect.

DHW + Distribution

The Domestic Hot Water + Distribution worksheet calculates losses through the building’s hot water pipes. Pipes are defined as either ‘circulation’ or ‘individual’ pipes. This worksheet models the heat losses of both or either type of pipework.

Circulation pipes are pipes that form a hot water circuit to and from the hot water store. A low-power pump continuously pushes hot water around the circuit, effectively making the circuit an extension of the hot water store. Circulation pipes are used in larger buildings, such as hotels, so that hot water can be made available quickly over a much wider area without having to draw off and waste large quantities of hot water every time a tap is turned on. Circulation pipes have an energy cost, owing to both the heat losses in the pipework and the electricity needed to run the circulation pump.

Individual pipes are pipe runs to end points of use (taps, shower heads, washing machines, etc.), either direct from the hot water store or from the hot water circuit, if there is one.

Wherever possible, in standard-sized residential units or homes, it makes sense to place the hot water store centrally, midway between the points of use, so that the need for a hot water circuit can be avoided. Using a narrower bore of pipework for individual pipes also helps to reduce energy use, because a smaller volume of water is contained within the pipework. Clearly, a balance has to be set between energy saving and providing a reasonable flow rate.

The PHPP assumes that any heat in the individual pipes will be lost, as it calculates on the basis that each tap or point of use will be used three times a day – enough time between uses for the heat to dissipate, even if the pipes are insulated.

The worksheet assumes that each person will use 25 litres of hot water daily. This is lower than Standard Assessment Procedure (SAP) but the default figure in cell K34 can be changed if needed; the PHPP suggests 12 litres for office accommodation.

SolarDHW

The SolarDHW worksheet models the contribution of a solar thermal hot water system, should the building have one. The worksheet takes as its starting point the net demand for domestic hot water as calculated in the DHW + Distribution worksheet, and the site’s location from the Climate worksheet (see Figure 7.11 opposite). The following information is needed to describe a solar hot water system:

•  Type of solar collector – in most cases, this will either be an ‘improved flat plate’ or a ‘vacuum tube’ collector.

•  Solar collector area – this can be taken from the manufacturer’s specification; ensure that the area is the net collector area, not the total collector footprint.

•  Deviation from north – enter 180° if the collectors face due south. In the southern hemisphere, enter 180° if the collectors face due north.

•  Inclination – i.e. roof pitch.

•  Any shading – for example, if the site is in a steep valley or is partly shaded by trees. There are three fields for this.

•  Type of solar storage – select from a range of store types and sizes or specify a bespoke type, if sufficient corroborated technical information is available from the manufacturer.

Although solar hot water is not a requirement of Passivhaus, its incorporation in the design will significantly reduce the building’s energy use, assuming the site, location and orientation are suitable, and is therefore encouraged by the PHI (hence the worksheet).

Climate

The Climate worksheet is a key component of the PHPP, as accurate climate data is vital to creating an accurate PHPP model. Monthly temperature and solar radiation data is required. By default, the Climate worksheet is set to a standard central European climate model. It is essential to change this to a climate model relating to the location of the project.

The PHPP contains partial and full data sets for selected locations around Europe and North America on a drop-down menu. The complete data sets allow the PHPP to calculate both the annual space heat (or cooling) demand and the heat (or cooling) load; the partial data sets only allow the PHPP to calculate annual heating (cooling) demand.

Figure 7.11 Amending the default altitude in the Climate worksheet.

If the project being modelled is located in a climate that is very different from any of the available climates in the PHPP, there are two options:

•  If the site is at high altitude, amend the default altitude for the chosen climate data set. In Figure 7.11 above, the default altitude of 30m has been changed to 180m. Change the default only if the difference in altitude is significant (say, 50m or more).

•  If the site has a microclimate that deviates greatly from the nearest climate model available in the PHPP, obtain climate data for the project’s specific location. BRE (www.bre.co.uk) and Meteonorm (www.meteonorm.com) both offer site-specific climate data for the PHPP. In the UK, BRE has created 22 geographically broader regional data models that have been ratified by the PHI and are currently free to download from www.passivhaus.org.uk/regionalclimate-data.jsp?id=38. Version 7 (2012) of the PHPP already includes this data.