Cost Analysis on the DATA HIU

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The DATA Heat Interface Unit is the most efficient HIU ever seen - proven in independent testing.

And it is also one of the most competitive HIUs on the market, BUT it's never the cheapest, so justifying why it's important to maintain quality equipment is necessary. Especially when it comes to people's homes and their cost of living.

The Cost Gap

It is not the place of this article to give away commercial pricing, however it is is fair to say that there is a gap in price between the an expensive HIU and a cheap cheapest HIU (similar loads) of around £500.

Our HIUs sit in the middle of this range - using the best quality modern control technology to deliver the best efficiency, but without needing an extensive array of mechanical valves that pushes the cost up.

So we are talking a saving of £250 between the best system on the market, and the worst, in terms of efficiency.

The difference to the end user over the years will, however, run into thousands of pounds.

Energy Costs versus Efficiency

It costs each end user approximately £100 if efficiency is reduced by only 1.2%

The spreadsheet below allows you to do the maths for yourself.

Google Sheet

Open Office Spreadsheet Cost Analysis


Its easy to state how much efficiency affects costs, but not so easy to work out how efficiency is affected.

We have devoted a great deal of effort into furthering the industries knowledge on the performance of heat network, and our open-source calculator is one modelling tool we can get some fairly accurate data from.

The calculator estimates savings at 21% on efficiency.

This is achieved by:

  • Permanent keep warm turned off
  • Heating return limited to 50C
  • £0.07/kWh

Comparison 1

Comparison 2

So with just a bit of a change in keep warm strategy, moving from a 47C permanent keep-warm to a system where keep warm is off, and setting control over return temperatures, we can potentially save over 20% on distribution efficiency.

Now, considering an HIU should be installed for some 20 years plus, that equates to a lifetime saving of over £3000 per system, from one small change. Even if the figures are a long way out, it is clear that selecting HIUs on the basis they are £100 cheaper than an efficient system is a false economy - or rather a symptom of our industry.

£3000 on the end users bill, for £100 in the supply chain's pocket. Thing is £100 may not sound much, but take 100 properties, that's a saving of £10,000 - a decent enough saving - but at £300,000 cost to the end users. And a lot of carbon.


Estate managers often have to rely on maintenance companies ensuring their networks are reliable an efficient, and we rely on the skills, honesty and integrity of our engineers to do a timely job where there is no technical oversight.

Modern HIU technology can help engineers ensure optimum performance, and report problems to them automatically.

  • No more pre-emptive servicing.
  • No more regular checks on performance.
  • No more wasted time on wrongly diagnosed problems and guesswork.
  • Improved service levels and response times.

The added benefit for installers is they get the best possible recommendation possible - a live system proving how good their installation is, and how efficient it is operating. They also have the benefit of second-by-second data streamed to their mobile phone on a system before they ever get to site, along with diagnostics on both the HIU and the heat network. For installers whose aim is to fix a system efficiently as possible, the use of this technology is the most powerful tool in the bag.

We know this because we are site engineers ourselves. We have for over 25 years provided first reaction site backup on all our products, and it is always in our benefit to find the root cause of a problem efficiently as possible. We first started using open-source monitoring technology for exactly this purpose - to help discover what was going on with a particularly complex mix of a wood burner and heat pump. The data led us to a key advance in thermal store technology still used in our HeatBank (TM) thermal stores.

Component Replacement Costs

Taking all components that may ever need replacing in an HIU, and averaging the spare part cost over the average lifetime of each component, gives an estimate component depreciation cost of £75 per year. This does not include labour.

The cost of labour will depend on the ratio of emergency component replacement over planned maintenance, where traveling to a single unit or unsociable hours are eliminated.

These figures are based on a well maintained primary system water quality. This is the most important factor in ensuring component failure costs are minimised.

Capital Savings

Providing an efficient heat network is not about spending more money on HIUs. Its about spending wisely.

Using an efficient HIU will also result in:

  • smaller pipe sizes across the development
  • smaller plant-room
  • a longer system life (avoiding problems such as limescale buildup in plate heat exchangers)

These savings, in themselves, justify using a decent quality HIU rather than the cheapest. But then again, bigger pipes and boilers means more money for installers, so what is the motivation to improve the situation.

Design and build is more and more common - out-sourcing the responsibility for thinking and quality. The big question then becomes, in the tendering for such contracts, are the minimum performance targets stated?

Now consider that current CIBSE guidance has a mistake in it, specifically relating to water velocities and pipe sizing, that ensures pipes are oversized and inefficient. What will you actually do when a year after hand-over it turns out the system is not fit for purpose? Who will now pay you (or rather the end-user) £200,000 to compensate for the extra heat losses of the system? Who would have the stomach for the court cases (remembering most expert witnesses will be working to the wrong book), when all one needs to do is pass the costs quietly on to the end user, because they know no better?

Cost to Reputation

If you are a developer or local authority, happy using the equipment your supply chain coughs up, what is your plan to deal with the damage to your reputation when it all comes out in the open that the end-users' interests, as well as the environment, have been completely ignored. Recent news events have demonstrated just how quickly it can turn very nasty for councils and big name companies, when the public kick back.

Surely it must be worth £100 on the cost of a £500,000 property to guarantee the properties work as well as they can, and the end-users end up singing your praise for delivering them quality homes that don't cost a fortune to live in.

Historical Failure Analysis

Records show a failure rate of stepper motors to be significantly less than 1%.

No electronic circuit has ever been recorded as failing.

The most common cause of valve replacement turns out to be a result of intermittent issues on a heat network that has caused an engineer to change valves to see if it helps.

Accelerated Testing of Stepper Motors

Stepper motors are subjected to accelerated testing in an oven at 65C to determine possible modes of failure.

Together with site information we would put a life expectancy of 10 years on a stepper motor. Possibly more as it is a brushless motor.

Responsive Servicing

Remote Engineer Dashboard

The instances of emergency call-out can be reduced with HIUs connected and reporting performance issues, as well as the number of wasted call-outs that require a follow up with the correct spares.

Systems that report an increased probability of component failure in the near future can be programmed into existing maintenance schedules.

The real benefits of such methods have yet to be demonstrated fully, and will come through having the ability to analyse data and further evolve the software that is used to identify problems until everything that can be predicted is done so accurately. Each unexpected component failure can be reflected on in light of the historical data before the failure, and where clues are found they can be checked out against other failure records and a function put in place to send an alarm to maintenance managers when other systems show symptoms.

The following 'emergencies' can all be avoided by automatic monitoring, checks, and alarms:

  • Leaks in central heating systems, or under-pressurised systems
  • Pump or control valve failure following general wear
  • Keep warm modes not set hot enough for rapid delivery in mornings
  • Central heating too hot or cold for times of year
  • Blocked strainers (or primary pipework)
  • Plant related issues that may result in multiple complaints, such as differential pressure across the network or primary temperatures too low to meet peak demand.

Such functionality can provide maintenance engineers with system summaries providing the full service history, advising the steps required next service, along with a list of parts, tools, and expected timescales for planned works.

Where a home display is provided by the billing system, it would be desirable to combine service alarms with messages to both engineers and occupants, so call-out times can be efficiently scheduled. Ideally the engineer only gets the nod once a problem has been identified, the system has picked a time when an engineer is in the area, and confirmed the time with the occupant via their home display.

The additional hardware costs are minimal, given a billing system already provides a communications backbone, and could be estimated at £150 per HIU to cover parts and labour. The services are generally driven by software alone, with little cost to deploy en masse given systems can be remotely updated.

With an emergency call-out costing in the region of £250, compared to £75 as part of a scheduled service, if an average of two call-outs per decade can be avoided, then this provides a saving of £175 every 10 years.

Hidden Costs

On a good percentage of sites there are snags. Dirt in pipes, pumps not linked to DP sensors, by-passs left open, and on and on. There is a considerable amount of time spent in finding and fixing such issues, and the cost of this is difficult to quantify, especially as difficult to find problems often require all parties to get involved, or multiple service call-outs are required to identify causes of issues.

With HIUs connected to monitoring, the vast majority of problems can be spotted from one's armchair. In fact, there is hardly a single problem with a heat network that cannot be identified through the data they provide. Blocked pipes can be located using the differential pressure estimates HIUs provide, and one can even go as far as identifying missing lengths of insulation from the second-by-second data.

Our best example from real life experience is a site where underground pipework had blockages caused by poor reaming of the ends. During commissioning it became apparent that something was up, as the further from the plant the poorer HIU performance was seen, to the point where design flows were not achievable.

With the consultant having sized pipes properly (i.e not over-sizing) the installers were quick to blame the design on the pipework. With the local authority using our HIUs for the first time they started to fear it was the HIUs at fault. A camera inspection of easy to reach lengths of primary pipework showed clean pipes, so blockages were all but dismissed. It was only following the addition of pressure sensors to multiple HIUs, and by creating flow through the network, that we were able to map pressure drops along pipework and clearly demonstrate a couple of points where we felt certain there must be a blockage. Further camera inspection then found them as located - fine plastic net created from pipe reaming that acted as a strainer for the rest of the debris.

The current electronic HIUs all have DP analysis built in as standard.

Spare Parts Logistics

Mechanical HIUs use different valves for hot water control, to heating control. They may also have additional valves for additional functions such as bypass flow, or return temperature limiting.

Across the range of electronic HIUs it is the same stepper motor used for hot water, central heating, an provides any additional functionality by the nature that the valves are electronically controlled to do whatever function is desired at any moment.

That means just one type of control valve to hold in stock, or on a van.

To an engineer on the ground, the ability to swap valves can assist testing and be useful in an emergency - if heating is not needed and the hot water valve fails, then as a temporary fix the valves can be swapped and service resume until a replacement arrives.

As an added bonus, replacing a valve will not introduce a change in settings, as one often sees. A new mechanical valve may be left on factory default, or be calibrated differently to the last, so manual adjustment will be required. An electronic system removes any manual setting processes.

pH Sensing

HIU Reconditioning

It should be noted that the HIUs that fit the standardised first fix bracket offer an alternative servicing approach - that of complete swapover of an HIU every 10 years.

Such an approach has the following advantages:

  • Rapid swapover of HIU - faster than individual components
  • HIUs can be flushed, tested and reconditioned in a factory environment
  • Reconditioned HIUs can be returned, along with a revived guarantee


The following table gives an estimate of life-time costs (10 years refurbishment cycles), covering all components, planned maintenance, emergency call-outs, and full refurbishment. In other words, this is a guess at the costs of lifetime parts and labour.

Description 10 year worst case 10 year best case
Component Depreciation £750 £500
Planned Interventions £150 £150
Refurbishment £350 £350
Emergency Interventions £500 £0
Totals £1750 £1000
Annual Cost £175 £100

As yet the efficiency and cost savings resulting from guaranteed low return temperatures have not been factored in. This would require an analysis of the heat generators. Heat pumps would show the best benefits. They work much better at low temperatures, and the use of a low temperature responsive system should provide significant improvements in COP.

For the purpose of HIU comparison, the cost of a replacement stepper motor is about 30% that of a mechanical valve, so they would need to fail three times as frequently to introduce additional costs by comparison if swapped out in regular maintenance. With some four years of records covering 10,000 systems and less than 1% failure, we know this not to be the case. In fact, the positional feedback from a stepper motor, and ability to double seat on closing, has made life easier for those if us responsible for reliability and service backup.

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