Category Archives: Software Tools

Tools that may be helpful in doing a self build

Solar PV for the self builder -Part 2

When the sun is close to the horizon Solar PV Panels generate less energy than when the sun is directly over the Solar Panel.

The reason for this is that the sun’s rays pass through more of the atmosphere thus reducing the sun’s energy (photon energy) on the PV panel. If it is an overcast day they will produce less energy. To translate this into numbers- in the winter when the sun is low in the sky (say 14 degrees from the horizon ) the total irradiance from the sun measures around 780 W/m2 (watts per meter square) with a clear sky. In the summer one would expect to see 1100 W/m2 (55 degrees from the horizon). The bottom line is that if one can point the solar panels perpendicular to the sun one will get a higher electrical output kw/h.

In order for consumers to purchase and compare solar PV panels manufacturers have agreed a way to compare the output power of Solar PV panels and this test is referred to as Standard Test Conditions (STC) . The test is done at an irradiance of 1000w/m2, at a air mass of 1.5 (approximately 42 degrees from the horizon) and at a temperature of 25 degrees. The value w/m2 is how solar irradiance is measured while the PV panel output power is measured in watts. The following calculator will help you understand how the output power of your PV System (in watts) is affected by solar irradiance and other factors. Check your Solar PV Output Power in watts.

IN-SOL Solar PV Calculator for checking a Solar PV Panel.
Solar PV Calculator

Most roofs have a pitch of around 35 degrees. The best direction to point the solar panels is usually south but with some solar PV installations, it is possible to have some pointing South and others pointing West in order to collect as much energy as possible during the summer. Meters used to measure solar irradiance are called pyranometers, Solar irradiance meters, or solar radiation meters. An example of how these meters are used to locate, measure, and check if your Solar PV system is working efficiently is shown below. The calculator above can be used with these meters.

PV Panel Shading

A factor that has a significant impact on the output power of a PV System is shading on an individual Solar PV panel. This can take the form of chimneys, trees or other houses. The reason for this is that if one examines each solar panel one will see that it is made up of individual cells wired together in series to make up a full solar panel (see below). If one or more cells are shaded when installing a traditional solar PV system (One inverter) the output power is reduced for the whole system. There are other solar PV systems that use microinverter’s or DC optimizers that will not be seriously impacted by shading thus the consumer will generate more electricity.

PV Panel Design
Solar PV

Another factor that significantly reduces the solar panel output power generated is the panel temperature. We are lucky in Ireland to have a mild climate with day temperatures not usually going above 20 degrees (on a good day). What this means from a practical perspective is that a solar panel in Ireland will generate more power than a solar panel in Spain on a cloudless day.

Solar PV Components.

The components that typically make up a solar PV system are PV rails which support the PV panel , roof brackets/hooks that connect the rail to the standard tile or slate roof and clamps that connect directly to a specified roof types such as zinc or steel roofs. There are separate pv panel mounting systems for flat roofs or ground mounting. If one wants to explore PV mounting system suppliers -use a google search for “roof mounting systems for solar panels“. As I used a zinc roof one must ensure expansion joints are installed in the pv rail every 3 meters.

PV Panel Types

There are three types of PV panel cells -monocrystalline (these aesthetically have an even black finishshown above), Polycrystalline which have an uneven shade of blue crystal cells and CIS types. Monocrystalline are more common and are slightly more expensive than polycrystalline and CIS are now more difficult to purchase (shown in part 1 of the blog). The options available when selecting PV panels other than the type above are length of equipment warranty and length of manufactures performance warranty. The majority of PV panels generate DC (direct current). All PV panels must be angled at least 3 degrees from the horizontal. PV panels produce DC power and to give you an idea of what 4 panels can produce and the energy they can generate for a load, loose connections or cable damage please see this video .

Inverter Options

Inverters are principally available in 3 types -one central inverter for a full PV installation without battery charging, a central inverter that has inbuilt battery charging facility and micro inverters for individual panels or a pair of PV panels.

Central inverters. The important factor here is the warranty length and how many MPPT (maximum power point tracking) channels does the inverter have. If one was installing 8 panels in two rows (strings), two separate MPPT channels would mean that the two rows of 4 panels would have their own ability to generate power independently of the other row (string) so for example if one row of pv panels got dirtier/shaded or a fault occurred on one panel the other row would keep generating at full power. As all PV panels are not exactly the same the separate MPPT channels allow for a higher output yield . When selecting an inverter one must match the PV Panels to a particular Inverter. Once this is done adding more panels can become restrictive and may mean that one needs to change the inverter again. If the inverter fails the whole system fails. If one needs to change a PV panel in the future the central inverter may also need to be changed.

Micro Inverters-simplify the installation of a PV system and permit simple expansion. It is really close to plug and play . Because they are paired with a PV panel they manage shading better than a central inverter. The voltage generated is also different to the central inverter in that it produces low voltage AC -the same voltage as all domestic appliances like fridges, washing machines etc. There is also less of a chance of fires because of loose connections/damaged cables. They offer full management of your PV system with apps and individual panel performance monitoring. Pv panels must also be matched with the individual inverter using the PV panel data sheet. This is one such calculator.

Microinverter Compatibility
Enphase Calculator


As stated before I personally am not in favour of using batteries for PV panel installations. The reason is that batteries are expensive, they are another failure point and I feel they are needed for vehicles more than PV installations. For example, a 300 litre water tank can store 20kw of energy at 60 degrees (a stainless steel water tank would cost around €1000-while a similar battery could cost €10,000 to €15,000 and still would need to be replaced after approximately 6000 cycles). All homes need hot water thus sending any excess electricity from the PV panels could be fed to a hot water tank. So instead of adding batteries why not consider changing the hot water tank and place elements at the bottom of the tank and the middle of the tank.

Another good idea is to switch to night time electricity which currently is half the price of the day unit to supplement the lack of PV power during the winter to heat the water tank.

My preference is to install a side arm heat exchanger to the water tank so that I can achieve better hot water stratification. Stratification is the creation of layers of hot water free from movement/mixing when one heats water. What happens for example is when cold water enters the tank at the bottom it can mix the stratified layers of hot water thus reducing the water temperature. It is difficult in Ireland to purchase water storage tanks that have simple devices fitted that maximise stratification with devices such as an inlet baffle on the cold water inlet .

To complement the above use of a water tank one can add a single shower pump and feed all showers from the tank.

Typical Shower Pump around €157

The above will reduce the use of electric showers which are the highest electrical energy consumption devices in a home. From personal experience, I can say that 150 litres of hot water (half a 300 litre tank) can provide 6 showers a day. Currently, I use off-peak electricity to heat half the tank.

If you are a new build one can plan to install the shower pump outside the house in an insulated chamber below ground level near the tank. This is what I have done to reduce the noise as we have a single-story home.

In part 2b we will look at how to analyze Solar PV quotations.

Self Build-Building a New Home-Self Builder

Factory Built or Site Construction 

There are many options today when deciding to build. One can use a factory built design or use traditional block work or timber frame on site. Some factory built designs are as follows by way of example .  One can select the level of input oneself such as only construct the frame and say the self builder can do the rest or let the builder/supplier do everything.

How much Work does a self builder take on.

As a self builder I would try and get the foundation, frame, roof and windows installed then one can work in the dry to finish it. One is left with indoor wall completion, plastering , air tightness, Heat recovery, Wiring, Plumbing, Rain Water Harvesting, House heating System, Water heating system, floor finish, Painting, furniture , kitchen more than enough work for the self builder. The above need to be well thought out before laying the foundation or erecting the frame and the finish design of the roof.

The Building Standards-Self Build

One needs to comply with the building regulations. Always remember these are the minimum standard. It is always better to go for a home that will last well into the future that is warm and supplies fresh air.  A lot of new homes built today are of a poor standard and this can be seen in the UK and Ireland. See example

The Sales Pitch

There are buildings that can receive different rating systems such as  LEED and BREEAM.  A good video on the good, the bad and the ugly of these can be seen here.  They focus on equipment and energy accessories so it is best to leave these and focus on the basics. What are the basics –Insulation, Air-tightness, WindowsHeat Recovery (fresh air supply), and minimising thermal bridging (heat loss through details on the build).  When one does the above one finds that the heating system is simple, the house costs very little to run and is healthy if the correct materials are selected and installed in correct sequence during the build.

The Gold Standard-Passive House

The highest energy standard to build a house , an apartment, school or commercial buildings is the passive house standard. It focuses on the basics and uses physics rather than rating systems to design the building.  All the calculations are done before the house is built on a passive house planning software package (PHPP) which takes into account for example how much solar heat the glass in the window will leave into the house, how much heat will be lost through the glass from the inside to outside, how much heat is lost through the frame, and the heat lost on how the window is installed in the wall. Every building detail physics are analysised to ensure that one ends up with a comfortable home.


Heat Recovery Ventilation (HRV) Selection Part 2

Selection of the HRV unit.

For those building to the Passive House standard the HRV is independently tested by the Passive House Institute. They provide a full list of certified units at the following link Passive House Certified Heat Recovery Units.   

HRV Efficiency (How is it calculated)

There are principally three methods it seems. One is the Supply method (used by manufactures) and this usually gives a higher efficiency value than the real world values. The Extract efficiency method is used to give a closer to real world value and then the passive house efficiency method which adds the following formulae to the Extract efficiency method.

Pel = real electrical power, W
M = mass flow, kg/h
Cp = specific heat of the air, kJ/kgK

The good news is that it appears if the HRV is certified to the Passive House standard then the difference between the supply method and the extract method  is very small.

In the near future I plan to connect to the HRV unit I purchased and view the efficiency values.

The Passive House certificate shows the following

HRV Calculation


Cost Efficiency

The most cost efficient unit I came across was the Airflow DV145 passive house certified unit for our 200 m2 house with an airflow capacity of 542 m3/h. I paid around €2200 for it. If one has a smaller floor area then more savings can be made by using a smaller unit. As a self builder technical support was important and their main offices are in the UK.

If one opts for a non-certified HRV unit a 12% reduction must be applied to the manufacturers specification . Some manufacturers might not renew the certificate each year so it is a good idea to ask if a certificate exists. The data must be entered in the planning software for the passive house. For those interested in the passive house planning software (PHPP)  there are courses run in Ireland frequently so I would suggest that one does this 3 day course (typical) and usually one finds the software discounted on the course.

It is an enjoyable course where one can select your own pace (the first time I did the course I wanted to listen and learn rather than calculate the performance of our own home). One such place is

HRV Self BuildTo be continued………


Contact Details:

Heat Recovery Ventilation (HRV) Selection- Part 1


There are two types of HRV units that I came across -Heat (HRV) or Energy (ERV). The ERV is used principally for recovering humidity  and heat. I selected a HRV unit,

Size Matters

When selecting a HRV unit it appears that one of the biggest mistakes is to select a unit that is too small but still satisfies the current regulations. What appears to happen in the competitive world of quotations is that a unit that just ticks the box comes in as the best price.

In selecting a unit for our home I selected a unit that has a manufacturers capacity of 542m3/h where the floor area of our house is 205 m2. Currently the unit is running at 31% of its capacity and it is maintaining a CO2 (Carbon Dioxide) level of around 700 ppm when the four of us occupy it . I use a stand alone CO2 sensor to measure the CO2 in different rooms. (I have not commissioned the unit yet as the internal doors/glazing are not installed).  

Another advantage of selecting a larger unit is that it can run more efficiently at lower speeds and generates less noise through the ducts or from the unit itself.

Some of the options from the manufacturer Airflow (my unit is the third from the right).

HRV passive house
A choice from one particular manufacturer.

September 2018 performance (with no heating switched on yet).

The graph below gives an idea of how the HRV works when managing heat from the house and supplying fresh air. For the coldest days of the year so far (2 degrees at night-in September) I put the unit into summer bypass mode the next morning (take in outside air directly and pump it around the house) because the sun was shining that day. The winter sun is lower in the sky so solar gain increases in the winter (when the sun shines). The house is made of timber/glulam construction. The main thermal mass is the concrete floor at the moment soon to be covered by a 32 mm thick wooden floor so the response times of house I suspect will change. The floor and wall temperatures are approximately 22 degrees Celsius.

HRV Software review and Control.

Example above of HRV in use in our home.

Sample Data in our home using Google Fusion to visualise the HRV data for a week in October. (see link below)

  • One can select the chart tab and visualise the graph.
  • Use the bottom graph to zoom in.
  • The data is from the 21 October to the 28 October 2018.
  • One storage heater rated at 1.7kwh was used for 5.5 hours a day off peak.
  • The storage heater was switched off for one day on the 23rd October.
  • The graph starts at midnight on the 21 October.
  • Each ref reading is every 10 minutes.
  • The CO2 reading vary between 480ppm and 700ppm when fully occupied.


All HRV units contain a maintainable part called filters. They have a number of functions.

  • Clean the air being pumped into the house, and
  • Keep the internal components such as fans, ducts and HRV housing clean.

One typically finds one coarse filter and one fine filter on the air supply into the house and a coarse filter on the extract air from the house before the extract fan. The coarse filter is typically a G4 and the fine filter is a F7 (Pollen filter). I installed a 400mm x 400mm  G4 coarse filter at the duct inlet so that I could keep the main supply duct clean. It is a bit more effort to maintain this but it will hopefully minimise the maintenance of the duct.

To be continued………


Thermal Bridges

As part of the passive house requirement one needs to eliminate or minimise heat loss through linear lengths or points around the house. Some of the thermal bridges in my build are typical of other builds. I hope to provide more details in the future.

One of the main linear heat losses is with window/door installations (its connection with the wall frame ). It has been said numerous times that selecting a high quality window/door and installing it poorly can equate to buying a low energy window .

As mentioned before I will use the free software called Therm to calculate the losses. The first detail to tackle is the glazing which was directly mounted in the frame of the house without a window frame.  These windows are 2.4 metres x .9 metre and there are 11 of these mounted on the south face.

The calculation of these linear losses can be expensive to get done so I will be doing the task myself and have it checked by others. I am surprised that good details are hard to come by on the web for free to help the self builder. One of the most time consuming exercises with thermal bridge calculations is drawing the detail. If one undertakes drawing this oneself using CAD (Computer Aided Design) software it can help to reduce the cost of the calculation.

When one needs to come up with a detail to minimise the losses there are a lot of products that help to keep the losses under control. These are semi-rigid insulation products like compacfoam, foamglass blocks, standard insulation, TECTEM, PU or rockwool and fibreglass products and aerogels (which is one of the highest performing insulators being made).

To date there appears to be very few online resources to guide the self builder or provide details that one can use before one starts a build.

Some background and details I found to date on thermal bridges can be found at the following links.

What is a Thermal Bridge

Leeds Beckett University

Scottish Thermal Bridge Details Link

Example of Heat Loss through a glass spacer

Below is an example of the thermal bridge calculations one needs to carry out to establish the thermal bridge performance values in W/(mk).

  • One draws the detail as a DXF file using a drawing package (or draw the detail manually in Therm)
  • Import the detail into Therm Software
  • Add the technical details such as thermal conductivity of each item
  • Tell Therm where on the drawing to stop the calculation (Adiabatic)-top and bottom of the drawing shown below.
  • Tell Therm what the internal and external temperatures are
  • Go to a spreadsheet and calculate the psi values of the thermal bridge detail for the passive house performance value.

When this is done one ends up with the calculation and an image like that shown below. In this image the glass is shown near the top right.

Drawing Detail


In the next image the colours show the temperature gradients. The purple colour is the outside temperature at -10 degrees.

colour infrared
There is thermal bridge software that one can buy where the software calculates the psi value without using a spreadsheet but Therm is free and there are courses available in Ireland.

If one wants to show the real design and installation details of the thermal bridge values for the Irish regulations rather than the accredited details (without a performance value)  one needs to use a certified thermal bridge accessors but this is not the case for the Passive House Institute.

We can all look forward to the day when standard construction details that are typically used in Ireland are already calculated for the self builder and there will be no need to pay to find out the thermal bridge losses . The Scottish accredited details (see above link) come close to taking the guess work out of construction.


Windows (Part I)

How many times did we see on Grand Design or other home build programs the stories of things going wrong with the windows/doors. Now after going through the process hopefully the following may help other self builders.


First of all the technical detail. The most important element of the windows is the glass. Some important functions-

  1. Capture heat (free energy) from the sun in the winter/autumn/spring to heat the house. (Called the g value)
  2. When the heat is captured or created in the house minimise the loss through the window (Called the Ug value for the glazing. )The Uw or U-value usually includes the whole window (including the frame ) but be aware that some window company’s may quote only the glazing value rather than the glazing and frame.
  3. Minimise cold air draughts (cold air descending at the window surface) that one may feel if one sits near a window (this is caused by the glazing not being able to keep the differential temperature between the inside and outside below 3 to 3.5 degrees Celsius. (eliminated by triple glaze systems)
  4. Maintain a sense of light in the room (the light level can be typically reduced by 30% (for triple glazed systems) when one tries to balance the above factors.
  5. Ensure that west facing and south orientation windows are correctly shaded (or by means of special glass) in the summer/autumn so that the house will not overheat .

The type of glass used in a self build can reduce the amount of insulation required in the house. One has to balance the g value ( g value represents the maximum amount of solar energy passing through the glass and 0.0 or 0% represents a window with no solar energy transmittance-if glass had a 53% = 0.53  g factor it would let 53% of the solar heat through. ) with the Ug value which represents the heat loss over a surface area in W (m2/k).

The glass that works in Germany may not necessarily work in Ireland. One needs to balance these two values to suit your house and orientation in the PHPP software.

Another important factor is the glazing spacer used between the panes of glass. Most high quality windows will use a thermally broken spacer to ensure that the minimum amount of heat is lost through the glass spacer. One can see this by viewing the colour of the spacer -if is it silver/metallic  then it more than likely has a high heat loss. If it is black it more than likely is a highly insulated spacer.

Window Spacer (Black)









Practical Choice

Options are available in general to have the windows opening out or opening in (with or without tilt and turn).  Tilt and turn mean that blinds and curtains need to be taken into account.

I believe there are only two or three manufacturers of sliding doors that are airtight. Other options are folding units.

  • Review the type of hinges (galvanized, steel, brass etc) and the handles specified (shapes).
  • Some opening out windows/doors have the option of a locking system  to ensure that a breeze will not affect the ventilation or damage them when left open.
  • Establish which doors need external key locks for entry .
  • Establish how many sets of keys you will receive
  • There is an option to have wooden or PVC windows clad with aluminium (evaluate which is more suitable in your environment such as being beside the sea versus fully sheltered).
  • Ensure the Ral colour touch up paint kit is available for small scratches and knocks that happen on site.
  • Establish if you want alarm contacts pre-installed.

Cost Choices

  • A window with minimum openings (more energy efficient) will be significantly cheaper than a window with multiple openings (less energy efficient).
  • A window that stays within the manufactures standard sizes and truck delivery size is going to be cheaper.
  • A window that has a non standard shape is going to be more expensive.
  • Sliding/Folding mechanisms and making them airtight is more expensive.
  • Establish if one can use glazing without a frame in your design (roughly 50% cheaper).
  • A certified passive house window will be more expensive. See link to certified components- Passive House Institute Certified Components

 Importance of Installing Windows Correctly

The frame that holds the glass and those used in passive houses will have an insulator such as cork or other insulation material separating the inside of the frame from the outside climate in order to reduce the heat loss. An equally important detail of a window is how it is going to be installed. This can account for over a third of the heat loss if it is just placed in an opening and secured with a steel band/bracket and then foam filled around the edges. So in real terms money spent on a high performance window/door can be negated completely by installing it poorly.

Below is a video I came across for guidance on installing windows  in a timber frame build (Ireland) with a breathable insulation on the outside and a sketch of an externally insulated block work building later on in the video. There are a number of videos in this series.

In my case I installed the windows in a wooden frame on a ventilated facade. As wood is a fairly good insulator (thermal conductivity of approximately 0.13w/(mk) ) I took the extra step of providing a better insulator around the reveal in order to improve the installation method and reduce the heat loss on the frame as the external cladding is vented with cement board. I am in the process of doing up the thermal bridge calculation using the free software Therm to calculate the actual linear heat loss (Thermal Bridge psi value denoted by the symbol Ψ).  The other type of heat loss is known as the U value and is a measure of surface area in watts per m2 per degree change (W/m2/K).

Where the window or doors were installed on concrete I installed Compacfoam  (rigid insulation) under the window/door and I will insulate and provide an airtight seal up to this material.

Window Frame Mounted on Compacfoam (insulator) in order to minimise the heat loss against the concrete floor.










Glazing (with no frames)

I installed some glazing in the structure of the building without the frames in order to reduce costs. The timber frame manufacturer, Matthew O Malley Timber Limited, rebated the openings and I then taped and sealed the glazing. There were 12 glazing units of 2.4 metres by 0.9 metres approximately.

I installed security tape in the rebate. I experimented with other security tape but found the following tape to be better-Closed cell polyolefin foam tape which conform to BS 7950 Manual Glazing Test from tapes direct in the UK.

Glazing openings with rebate in timber.












As the structure of our home is made with gluelam this helps to minimise the movement in a timber frame build to facilate installing glazing without a frame. I am not sure if glazing can be installed directly in a standard timber frame build.

Other important factors to consider are:

  • air-tightness (the normal passive certified window will have two or three seals mounted in the frame) .








Self Build (Tools and Aids)

There are a few tools that I found very useful as a self builder (which are free).

One such tool is Evernote.  As self building involves plenty of research and the need to access information. This tool has proved invaluable for me to store information, share information, find information and make it accessible on a smart phone, any computer and automatically back up the information (nothing worse than loosing or not being able to find information). It also allows one to take pictures and have these stored in the same place.

All one needs to do is tag the information (a tag example could be the word insulation) -when you store the price/information you found on the internet about insulation it is stored with this tag and any other insulation data found over time. All pdf documents (these are usually research papers) can be stored also. There is an option to buy the premium version at €40 a year then the individual pdf content of the documents can be searched.

Another tool is Autodesk Design Review 2013. This tool allows you to open autocad files that your architect or engineer may have used for your build. It also allows you to edit these with your comments , take measurements of the drawing and draw simple shapes to highlight issues.

Another tool worth mentioning is Autodesk DWG Trueview. This is more similar to Autocad as it is mainly a viewer (allows one to open files).


A tool that allows one to calculate the heat loss of thermal bridges is Therm. It was developed by Lawrence Berkeley National Laboratory (LBNL) and again it is free. This tool will show you how cold (and the heat loss) your floor/window reveal etc is going to be near outside walls and the actual performance value so that the real heat loss can be calculated. (One can easily get a feel of the importance of this detail and the energy lost if you see mold/condensation around windows/doors etc ). This software will show graphically how much heat is lost (once calculated) and the temperature/heat loss you can expect on details such as window frames, door thresholds, the steel ties in your block work, the steel beam sitting on your inner wall  or foundation etc.

There are two parts to calculating the actual heat loss – the first is drawing the detail (fairly simple and involves time) and the other is the actual calculation (tricky I feel for a self builder). If one draws the detail this can save costs if a third party does the calculation for you).

Thermal Bridge
Thermal image of temperature changes in a foundation with low heat loss. The right hand side is the internal floor. The blue, purple and green colours are low temperatures. The green colour is 5 degrees Celsius.

The above foundation with no insulation. The inside floor has a high heat loss when the inside room temperature is 20 degrees Celsius. The small red line on the floor shows a wooden floor installed thus delaying the heat loss.


This tool allows one to model in 3D your house design and carry out a walk through to get a feeling of the internal or external design. It also is used by the passive house institute on their energy balancing software PHPP so it is a worthwhile tool to learn.


Other than a smart phone which is a real help when one wants to send/receive files, images or emails and keep things moving on site a device called the Samsung Note 10.1 (2014 Edition) makes documenting ideas and drawings a great resource while on the move. It is only one of a few devices that has a real pen and sketch pad that allows one I feel to replace a piece of paper because one can rest your palm on the screen like a piece of paper and write or draw.

Sun and Climate

Sun Surveyor Lite predicts and visualizes Sun, Sunrise and Sunset positions and times with a 3D Compass on your smart phone. It is useful in identifying the site layout and potential shading issues from trees etc. One can simulate the sun at different times of the year. If one want to do the exercise on paper then this web may be of help-