T-Zero – Ways to reduce the environmental impact from existing housing
This is my site Written by admin on April 12, 2009 – 3:58 pm


T-Zero is a web based tool that enables the user to provide details about their property, and an amount of money that the user wishes to invest in improving the carbon footprint, energy usage (i.e. reducing it), payback period, bill savings etc

It is quite comprehensive, but doesn’t include some options. Below is the dialogue with a member of the T-Zero consortium about some odd things that happened with the tool. Note, the current version of the tool is a ‘test version’, which the consortium have invited people to test out and feedback their comments. The full version will be released in May 2009. It is a major step forward with helping people in the decision making process for ECO retrofit. Discussions are underway about future proofing considerations.

Question #1 – Initial Usage of the Tool


Having fed all this information in, one gets the above results. A -£90.01 doesn’t quite make sense. The picture below would indicate a carbon negative situation – I presume.


So what would help is if the follow information which is obtained when you click on “Best CO2 Saving”, also contained the savings – which, in theory should add up to -£90.01. This would seem to indicate that there is no saving i.e. it will cost you more. If the info below had the additional column, it could help explain where the savings were accrued:-


A loss of -£90, I assume, is due to the cost of the woodchip for the biomass boiler? Difficult to assess.

I have now seen the PDF which summaries the performance:-


This helps a little, but splitting out the savings against each of the measures would help. Also I’m not sure going from a C to a D for the EPC will work – again I’m not sure why that is the case. It also doesn’t appear to have any payback period.


My view is that yes – I want to maximise my savings on CO2, but also want to maximise my savings on fuel.  Could an approach be to install additional insulation (external cladding) and experiment with the options on heating? (assuming the biomass boiler is causing the extra cost). So, even though I have cavity wall insulation, would additional cladding help reduce the need for heating eg a wood burning stove ?

Is there an “expert mode” where room measurements can be included, wall thicknesses etc ?

Response #1

You are correct in your central assumption:  the addition of the biomass boiler, whilst great for CO2 reduction, can result in an increase in fuel bills if you are replacing a newish gas boiler.  The EPC band – a measure of the fuel costs required in a typical property – therefore also reduces.  If a package isn’t saving you money, it will never pay back.

There is a feature beneath the Package Selection table which allows you to exclude certain measures (such as biomass boilers) and experiment with the resulting packages.  Varying the budget can have a similar impact.

As for breaking the fuel savings down for each individual measure, this is very difficult to do using the ‘package’ approach that we’ve adopted, though it is something we hope to incorporate in future versions.  Ditto the ‘expert’ version:  naturally, for ease of implementation, we have designed the tool to be as straightforward as possible, but over time we will develop features for users to undertake more bespoke analysis.

Question #2 – External Insulation Option

I don’t believe there is an option for external insulation in order to improve on the u value. I have contacted Weber and CarbonEco who are in the process of giving me quotes for achieving a u-value of .14, but its doesn’t seem to be an option on the tool. Why is that ?

Response #2

We’ve purposely designed T-ZERO v.1 to be as straightforward as possible so that (a) we haven’t overcomplicated the calculation engine, and (b) there aren’t so many options that users are scared away.  A level of complexity has been sacrificed.

So we’ve tried to offer just one option for each measure, and attributed it with a generic performance.  For EWI, we have currently chosen to use the building regs U-value of 0.35.  We do not want to attribute specifications that outperform the norm because there is a danger that users will not see the benefits that T-ZERO predicts if they install the measure (but don’t insist on the lower U-value), but also that we can be accused of given preference to certain technologies if we improve the modelled performance of some measures but not others.

Having said that, there is some flexibility here, and I certainly agree with the argument that if you are going to have EWI done (and pay for scaffolding, labour etc), you may as well pay the marginal cost to reduce the U-value much further than the building regs.

So in the short term I’ll see if the consortium agree to reducing the modelled U-value a little before version 1.0 goes live.  In the longer term we’d like to create a version for professional users which allows them to adjust u-values, unit costs, performance etc.

Question #3 – Future Proofing

I think one of the most serious issues that needs careful consideration is about the “use of current building regs”. Given that the regulations will become more stringent over time, simply meeting today’s regs will quickly become “out of date” over the coming years, which could mean more retrofitting.

If I am about to make serious changes on my house, then I really what to have the choice to  “future proof” those changes now so that I do not have to spend yet more money later doing additional work. In my humble opinion, give the user of the tool the choice to go for either current building regs standards, or higher standards would enable the user to perform a better cost benefits analysis and hence determine whether an up front investment now will save more money in the long term.

Ultimately, this is about sustainability which involves taking a much longer time horizon that today’s current building regs.

Response #3

Yes, this argument has a lot of weight.  I’ll discuss this issue with the group when we meet in a fortnight’s time, but I do agree with what you are saying.  Hopefully we can implement this over the coming weeks.

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