Weather Tool Comments
Help Tool
Not being used to using a Pychrometric Chart (or many of the other tools within the weather
tool for that matter) it would be useful if the help too explained how to read the data portrayed
on the screen. (If I hadn’t got a copy of “Introduction to Architectural Science” I’d be even
more lost.)
For a truly interactive tool perhaps the user could hold the curser over a particular piece data
that is plotted on the chart and a help bubble would pop up to explain more clearly what the
data is telling you/how to read the data.
Another instance, looking at the Solar Position tool and calculating the Best Orientation there
is a host of data displayed but I am unable to interpret it all due to lack of awareness on my
part and an apparent lack of explanation in the help files.
In summary, a clearer explanation of how to interpret the data on this and other tables/graphs
is required.
Zoom
Zoom but no pan tool or scroll bars? The zoom tool only seems to zoom in towards the centre
of the screen. How do I inspect data i.e. monthly ranges etc. that are off the edge of the view?
Psychrometry Chart Overlays:
Relative Humidity
Szokolay places a great deal of emphasis upon the 50% RH line and it relation with comfort
temperatures. Given the Weather Tool relies heavily upon his data perhaps this line should be
graphically represented in all cases. Also the RH lines have no numerical support, this would
be helpful.
Roaf and Nichol vs. Szokolay: Thermal Comfort and The Heating Season
Szokolay references the work done by Roaf and Nichol, he stops short of explaining a
number of important observations that emerge from their work. Having referred to the books
“Ecohouse” and “Closing the Loop” it can be found that Sue Roaf, in conjunction with the
amended Humpherys and Nichol equation, also uses the Nichol Graph.
The critical thing here is that Roaf/Nichol also recognise that the comfort temperature at which
heating is required is, in part, culturally derived and can even vary between building
typologies (e.g. UK residential 19C, UK offices 21C). This data is also recorded on the Nichol
Graph i.e. when the anticipated comfort (as equation) falls below the culturally derived
temperature heating is required. Only then can the comfort temperature (TC) be determined.
Szokolay’s Comfort Criteria charts do not seem to recognise this particular cultural aspect. To
this end is can be reasoned that additional regional, culturally derived data is required if a
more realistic regional heating season is to be described.
Finally Roaf has developed the Nichol Graph further so as to identify the passive solar
heating options. This is achieved by plotting the mean solar intensity (monthly solar
irradiation) underneath the Nichol Graph as a bar chart.
All quite informative when designing a building based upon Passive Solar. The Monthly Data
within the Weather Tool demonstrates that you have all the data, but the composite graph by
Roaf (to my mind) explains things in a more legible manner.
Slide bars
It would be useful if a there was a more accurate understanding of the units i.e. insulation =
very low, low, medium etc. Why not have a data window (possible editable) that indicates the
U-value achieved using the slider i.e. 0.25w/m2k? A similar means of accurate data could be
implemented on other siders. (Some of the sliders offer this level of data others don’t)
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It would be good if you could adjust the thermal mass using a slider so as to gain a
better understanding of the potential/benefits. The slider would show units of W/m2
energy (to tie in with earlier comments on sliders).
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To assess the benefits of thermal mass, surely the internal heat load have to be
considered. (These would be dependant upon use type i.e. cellular office, open plan
office, house etc.)
The pros and cons of exploiting solar gains and the impact on comfort (pg55-57)
Psychrometry Chart Overlays - Making Iterative Design Easier
The fly out menu with all the overlays could be simplified so that it is not quite so “top heavy.”
This could be achieved if a number of the existing overlays were listed down the side of the
screen in the principle menu bar.
The overlays that could be included in this manner would be: Passive Solar Heating, Thermal
Mass Effect, Mass + Night Purge, Nat Vent, Direct Evaporative Cooling, Indirect Evaporative
Cooling, Multiple Techniques).
Rather than the fly out selection system a check box could be used to turn on/off the
appropriate heading/overlay.
Such a means of presentation would allow the respective sliders to remain permanently on
display, as a consequence a real time understanding of trade offs can be gained when using
the Multiple Techniques tool. Also the Multiple Techniques could be engaged simply by
checking all the boxes.)
Review of Overlays
The comments observations and queries below have been derived by reflecting upon the
Weather Tool and the book Introduction to Architectural Science by Steve Szokolay.
A problem that I have consistently run into, both in the Weather Tool and in Szokolay’s book
is getting a definition of the Control Potential Zone (CPZ) and what it seeks to represent. You
will see below how this remains unclear. Does the CPZ seek to illustrate how the level of
thermal comfort can be extended in every case? Or does it means something else?
Passive Solar Heating (Potential)
The sliders shown include glazing ratio, insulation and efficiency.
1) Szokolay does not clarify how the efficiency is determined, nor does the Weather Tool.
Please could you clarify this matter, does this refer to the Solar Heat Gain Coefficient?
2) The weather tool does not offer any numerical data on Vertical Irradiation. This would be
informative, as over time it would allow a more heuristic understanding to develop.
3) Szokolay’s calculations allow for the Building Conductance, this includes both ventilation
and thermal conduction heat losses. The Passive Solar Heating overlay does not seem to
account for ventilation heat loss (I presume that the “insulation” slider covers the fabric
conductance).
4) To remain with building conductance for a moment, how can is this estimated without an
understanding of the area of the building envelope?
To improve the accuracy perhaps there needs to be a guesstimate building modeller with
sliders for wall U value, glazing U value, roof U value, building area, number of storeys
storey height and airtightness. I know it makes simple tool more complex but if a suitably
realistic stab in the dark is to be made it is arguable that this data is necessary.
5) Back to “Insulation”: It would seem that you can have a super insulated 100% glazed
building (admittedly perhaps common sense should rule here, but is there a way of
having the software preventing such fantasies?) – see comments on sliders also
6) There does not appear to be any feedback, numerical or others wise, to allow an
understanding at which the point at which the Passive Solar Heating potential will fail to
provide adequate heating. Such information will be greatly informative in the initial stages
of developing a design. (Szokolay gives the external temperature.)
Having said this it may be that this data is conveyed by the left hand side of the CPZ,
however the help tool is unable to clarify this. In which case see comments above on the
Help Tool. (If it is this edge of the box then what is the rest of the box trying to tell me?
7) Passive Solar Overheating Potential: If you have a 100% glazed façade it is likely that
you’ll cook the occupants. Using the Passive Solar Heating data can the Weather Tool be
used to inform about overheating potential?
8) See notes on sliders and informing the user on quantities and units.
Thermal Mass Effect
If I am interpreting the Weather Tool correctly then in order to determine the impact of thermal
mass you have followed Szokolay’s reasoning that “in a very massive building the indoor
temperature would be practically constant at about the level of the outdoor mean.”
1) As far as the software is concerned it would be useful if this implicit assumption were
spelt out more clearly (it would seem that that is what the reasoning has become as it is
not described anywhere).
2) The Weather tool does not aid with developing an understanding of what constitutes “a
very massive building” or indeed “thermal mass.” It would be useful if there were some
more data available on this so as to aid brief development. This could be within the help
tool or some text that appears on the Psychrometric chart.
3) Related to all the above items: Currently only one option is available “High Thermal
Mass.” This is problematic as the availability of thermal mass is often affected by building
type as much as by construction technique (i.e. open plan office vs. cellular office/house)
perhaps a new slider or selection tool could be introduced to allow for this. Furthermore in
offices especially the availability of thermal mass is affected by the construction technique
(flat or coffered ceilings as BRE Digest 454, BRE IP 6/01). Clarification on this would also
be beneficial.
4) Within the Weather Tool it is not clear how the zone covered CPZ is derived or quite what
it represents. Having said this it may be that the data conveyed by the right hand side of
the red box/CPZ, illustrate the upper mass limit, (but what the left hand side, the lower
limit, of the box represents remains unclear) sadly the help tool is unable to clarify this. In
which case see comments above on the Help Tool.
Mass + Night Purge
As above.
Nat Vent - Air Movement
1) Air speed? How fast? See notes on sliders and informing the user on quantities and
units.
2) As the air speed increases the CPZ extends to the right. What this actually means
and how this informs a design is not clear as there is no help covering this matter.
(Only by referring to Szokolay do I find that it is the are above the 50%RH that is of
particular interest with regard to cooling through air movement and that the
boundaries define the range of outdoor conditions under which air movement has the
potential to render indoor conditions comfortable.)
Direct Evaporative Cooling and Indirect Evaporative Cooling
1) It is unclear how to interpret the data plotted in the Psychrometric Chart. Again the
Help tool would clarify what the diagram is seeking to explain and the use of this
information to the designer.
Hourly Data Points
When “Hourly Data Points” is selected you can change the dates. Each month has its own
comfort zone yet if you select “All Year” you get a very narrow average for the year. This is
not an entirely fair reflection of the range of comfort temperatures available, as on a monthly
basis these vary (as shown by the display of the monthly calcs.)
In order to reflect range of comfort more accurately in addition to the averaged “All Year”
average display and “Year in View” overlay would also be useful. The Year in View would plot
the Comfort Rages for each month (Jan-Dec) on one view. Thus an appreciation of the true
range of comfort zones over the course of the whole year can be gained.
Passive Design Analysis Tool
 The weather data does not appear to include rain fall as when the calc is run i.e. the
computer throws up “ERROR: Climate can not be determined. You should check the
data in this file as zero rainfall was recorded. You may need to enter values
manually.” Is the weather tool data due to be up dated so as to include rainfall?
Comparison to Psycho Tool
 Activity Levels – the Pscho Tool is better – more informative (and humorous i.e. “a
little to relaxed,” ”death” etc) weather tool.
 No clothing data within Weather Tool there is in the Phycho Tool. To assist the
assessment of thermal comfort this would be useful in the weather tool also.
 The automatic Human Comfort slider along with the “dynamic coloured underlay” to
the Phycho Tool is informative when trying to understand the effects of ventilation and
radiant temperature. I believe that it would be beneficial if it were included within the
Weather Tool. (Though I must confess that I am not certain about how the radiant
temperature and works with the dry/wet bulb temps on the Psychrometric Chart. In
principle this is because I need to check out what exactly the radiant temperature
measurement refers to…...)
 The floating cursor of the Pscho Tool is informative. Could this be added to the
Weather Tool?
Monthly Data
The Temperature Graph has three lines, if I hadn’t read books by Sue Roaf I’d be confused (I
presume that they relate to Tmin, Tmax and TC….or the SET version of such things).
Perhaps by pulling each band out in a different colour and tying the coloured lines back to a
key an explanation would be more apparent.