Regional Winners

Please tell us about a project you are particularly proud of – what was the problem and how did you solve it for the customer?

Fortunately, our work nearly always comes from recommendations, which is always a good start from an installer’s point of view. This job; however, wasn’t; they found us through an internet search. So, they reached out and wanted to discuss the project.

The project plan was to build a new timber-framed building. It comprises of four beds, two attic rooms, an office and a workspace with a detached garage. The total floor area was 218m2.

I met with Sam and Rosie, and after the meeting, we came away with four main challenges.

1. Space limitations
2. Fixed budget
3. The client wanted the lowest ongoing running costs
4. High equipment specification

Usually, we would fix the equipment specifications and then ask for the required space. When exploring options for the plant room, the garage would have been a perfect choice, but as it was detached from the house, the costs pushed it over budget, so the garage was out.

This then made the only option on the top floor of the office. This determined how we would develop a design; it wouldn’t make the nicest of plant room layouts, but sometimes it’s function over form. We had to select plant equipment small enough to be located on the top floor.

To maximise performance, we advised using an air source heat pump to provide heating and hot water, and an MVHR system to manage the ventilation.

Initially, Sam and Rosie looked at the underfloor heating to be installed on all three floors. I explained that we could change the design and link the MVHR to the heat pump, remove the underfloor heating on the second and third-floor bedrooms, and supply the heating through the proposed MVHR system.

This also allowed the client to do cooling, often overlooked in new builds. Once the design had been calculated, some areas had a relatively high cooling load. Removing the underfloor significantly benefitted the budget, which the clients were happy with.

Sam and Rosie had already commissioned another installer to carry out the domestic plumbing works and a PV system; we had the opportunity to advise them and change some of these works to maximise the design. This also removed other costs like expensive individual room control for the ground floor underfloor system and pump packs. Our system design had these built in.

The technical side of what goes into a project like this one might look complicated, and in some areas, it is, but like anything, if we break it down into bite-size pieces, it becomes a standard process. At the start of any technical design, we always look at the following:

Ventilation heat loss is when warm air leaves the house; cold incoming air must be warmed to replace that heat. This may be through open doors, windows and ventilation, but it will also be through gaps and cracks in the building structure. In new builds, ventilation loss is one of the most significant heat losses, if not the largest. The importance of this will become more apparent a little later.

Fabric heat loss is conducted through the fabric of the building – its walls, roof, ground floor, windows, and doors. The building regulation’s part L 2022 limits both ventilation and fabric loss.

Ventilation rates are required to keep the air quality and building background to a required standard and are often overlooked or undervalued in new builds up until recent changes to building regulations document Part F 2022. Heat gains are simply what they sound like. They are from anything that generates heat; some things may be obvious, like fridges, TVs, washing machines, and tumble dryers, while others may not, like external fabric, windows/glazing, hot water cylinders, pipework, occupancy, and even down to the family pet. Heat gains are set out in the building regulations Document Part O 2022 Sanitation, hot water safety and water efficiency are hot and cold-water use, coming under the building regulations approved in Document G 2016.

Why MVHR?
Firstly, well-insulated buildings have a low heat load. What is often underestimated is that it is tough to achieve the ventilation requirement with standard extraction methods. Typically, windows are opened to combat poor ventilation, which lets the valuable heat out very quickly. Assuming we tried this with this project with the standard ventilation requirement, we would need to accomplish the following ventilation and extraction rates.

Ventilation rates:
Five bedrooms would be 43 l/s or a minimum of 0.3l/s per 1m2 of habitable floor area, whichever is greater. The total habitable area 218m2 * 0.3 = 65.4 l/s is greater than the five-bedroom minimum of 43l/s. This sets the ventilation rate to 65.4l/s.

We then need to set extraction rates:
Extraction rates are assumed continuous (Part F 2022). The sum of all extract ventilation in the dwelling on its continuous rate should be at least the whole dwelling ventilation rate. This gives an extraction rate to the project of 65.4l/s. The individual room extraction rates can be found in Table 1.2 of part F 2022.

Doing this with background ventilators creates a lot of holes in the nicely built new project, and with the air tightness valves built less than 3m3/(h·m2) at 50Pa. It isn’t achievable and wouldn’t meet Part F.

65.4l/s = 235m3 per hour.

We can calculate the amount of energy to heat this by using the formula: QV = 0.33 × V × (Tin – Tout)

This would be: 0.33 x 235 x (23.2)

23.2 is the difference in design conditions of the temperature between the inside and outside.

This gives 1800 Wh or 1.8kw

Another way of looking at it is that for every one-degree temperature drop outside, it will require 77.58 Wh to warm up the fresh air coming into the property.

Looking at an average UK day at 8°C, this would be a 13-degree difference. This would be 1,008 WH or 1KW of energy every hour of every day. This is a significant loss.

MVHR can recover up to 96% of the energy from the extracted air. Internal heat gains can be maximised in the winter; overheating gains can be reduced in the summer. We must consider the energy use of the MVHR unit, which is defined as watt per l/s. This is an energy use but will save more energy than it uses when designed and installed correctly.

The specifics of this project:

• Heat loss without MVHR: 5788 Wh
• Heat loss with MVHR: 3988Wh
• Saving with MVHR is 1800 Wh

Choosing MVHR will give a 35% gross energy saving at design conditions. This reduces heat-generating equipment capacity, such as an air source heat pump.

MVHR was the apparent choice for energy saving. The gains from highly insulated homes can be maximised. Air quality and comfort levels are vastly improved, and by using MVHR, we had the option to provide supplementary heating and, more importantly, cooling for the summer at minimal additional cost to the dwelling. The importance of this technology cannot be underestimated.

The above calculations are based on the standards, but in real-world applications, ventilation can be lowered by applying air quality monitoring and site-specific settings, including a night set back mode; this can be improved to over 45% net energy savings; we don’t run the fan speed any higher than needed, not over ventilating. This maximises energy recovery and running costs. Technical knowledge of air source heating and cooling with underfloor and post-MVHR heat exchanger.

Once the MVHR had been fixed, selecting an air source system was straightforward. One consideration that is sometimes overlooked is the modulation rate of a heat pump system. To understand this, we need to look at the total watts per degree of rise. This is calculated by taking the max design condition. In our case, this is 3,900wh, and dividing this by 23.2 gives us 168.10Wh per degree of rise.

We take this number and look at the day’s average temperature to determine the required range. The average UK day for the north west is 8°C. This will require 2,185 Wh.

We selected a unit with a range of 2Kw to 8Kw. We could have gone smaller, but this was chosen to recover the 250 hot water cylinders within 90 minutes, a suitable time for a growing family. A 100-litre buffer was selected to provide some additional volume; two heating circuits came from this to provide LTHW to the underfloor, and the heater coil for the MVHR is reversible for cooling and weather-compensated.

We had the chance to increase the pipe centres to the underfloor heating to 100mm, which gave the lowest heating flow temperature and more volume for summer radiant cooling.

Project design parameters:
Total building fabric loss at design -2.2°C

3,900 Wh

Average watt per m2 at max design conditions:

17.88 Wh

Total watts per degree of rise on of 23.2°C

168.10 Wh

Heat gains winter

850 Wh

Heat gains summer

4,500Wh at 28°C

Ventilation and extraction rate: 65 l/s

All calculations are based on the following U-valves.

External walls, including semi-exposed walls U = 0.13 W/(m²·K) Party Wall U = 0 Floor U = 0.11 W/(m²·K) Roof U = 0.15 W/(m²·K) Opaque door (less than 30% glazed area) U = 1.0 W/(m²·K) Semi-glazed door (30–60% glazed area) U = 1.0 W/(m²·K) Windows and glazed doors with greater than 60% glazed area U = 1.2 W/(m²·K) Roof Windows U = 1.2 W/(m²·K) Rooflights U = 1.7 W/(m2·K) Ventilation system: MVHR with heat recovery @ 92% Air permeability 2.6m³/(h·m²) at 50 Pa Measured at insulation and final main heating fuel (space and water) Mains electricity Heating system Air source heat pump with underfloor and MVHR post-heating coil Design flow temperature: 30°C. The heating system controls weather compensation with proportional internal temperature influence per zone.

Which products did you select for the job and why?

As a small company, we pride ourselves on specifying products that we would have in our own homes. Offering a high-quality product portfolio has the advantages of:

• Making it more efficient as we can standardise complex installations, which often don’t go together.
• Holding stock and keeping deliveries to a minimum. This is important as we are trying to lower our carbon impact as a business and make the client aware of the same approach.
• Reducing waste by 25% and passing this saving on to our clients when possible.
• Giving all of our clients continuity and ongoing post-installation support.
• Offering equipment that we can remotely monitor.

This was the equipment used:

• Stiebel Eltron UK WPL classic 17 air source heat pump for heating and cooling
• Stiebel Eltron UK HMS trend heat pump interface
• Stiebel Eltron FET controllers
• ComfoQ 450 ERV MVHR unit by Zehnder
• Ducting and ventilation by Zehender
• 250-litre Tempest heat pump hot water cylinder by Telford
• Stiebel Eltron UK 100-litre buffer
• Two circulation units by Flamco
• Lawton copper tube pipe
• Peglar for pipe fittings and valves
• Armacell for pipe insulation and lagging

We chose these brands because we have a lot of trust and have built a close working relationship with our selected manufacturers. Our work is specialist, and, where possible, we source locally and use products made in the UK when possible.

We use Stiebel Eltron UK Bromborough, which is about 60 miles from our working base. Although the manufacturing isn’t done in the UK, the training and ongoing support are critical to us as a small company. This is because:

• The range of inverter-driven air source heat pumps by Stiebel Eltron is market-leading
• They have some of the highest SCOPS on the market
• It was essential to offer the client the most efficient equipment for the project
• Quiet in operation (a great advantage from a customer point of view)
• Energy Class A+++ @ W55
• Remote monitoring through the ISG (internet gateway) to give the client offsite support, by ourselves and the technical support if required
• The ISG has built-in energy monitoring; this includes power consumption and heat delivered. It gives the client accurate energy use and valuable data for making onsite system changes for maximum efficiency

We chose Zehnder UK as our MVHR supplier:

• The Zehnder ComfoAir Q are simply the best on the market
• Tried-and-tested, complete system
• Automatic modulating true summer by-pass
• Heat recovery efficiency up to 97%
• Integrated humidity sensor to provide a comfortable, healthy, energy-efficient indoor climate
• Remote monitoring

We chose the pipe from Lawton Tube Coventry because:

• High-quality copper tube as standard
• Copper is the preferred method for our plant room installations
• We can recycle the waste, knowing it will go back into the supply chain and not into landfills, as it has a high value and can be recycled
• Copper is a nonferrous system, which helps with the system’s water quality
• Made in the UK

We chose Peglar Xpress Doncaster because:

• Peglar Xpress pipe fittings have been a go-to for nearly 10 years; the system offers a cleaner, neater install and is hot work-free
• Made in the UK

We used Armacell insulation Oldham because:

• Having moved to Armaflex pipe insulation for all our installations four years ago, we have found that we can achieve a better finish and improve our heat losses
• Lagging is a significant part of what we do; energy is expensive, so we put a lot of time into doing it right to minimise heat loss
• The product produces less waste as it can be bent and formed around the pipework rather than forming mitres
• Overall, it gives a more professional look, which clients have commented on multiple occasions
• Made in the UK

Tell us what was different or unique about this job? Why does it stand out?

The project was great this year because it allowed us to promote and install the perfect setup for a modern home. Managing the seasons and efficiently heating, cooling and ventilating all year round gave the client an ideal home environment. But most of all, the clients stood out for us; they had 100% focus, and once they committed to our design and programme, they just let us get on with it. They made some changes along the way, and we were happy to alter our design. They added WC that we still needed to account for, and we redesigned some ductwork to accommodate the extraction.

The bedrooms stood out for us as well. The simple rectangular shape consists of a central corridor with a floor area of 16 m2. This required very little heating; each bedroom only needs around 200Wh under maximum design conditions. This is only 12.5 watts per m2. Some properties we work in have heat losses of 150 watt m2! This is partly due to the building’s insulation levels, standard-height ceilings, and modestly-sized triple-glazed windows. But the system we installed plays a significant part. It can recover heat from higher-heated areas and distribute it around the bedrooms. We overheat downstairs slightly with the underfloor, and the MVHR distributes the heat around the space. If it gets below a specific temperature outside, the second heating zone will come on and provide additional heating to the air when it passes through the MVHR system.

To give an example of how effective the system is at recovering heat in the bedrooms:

On an average UK day, the heating load is around 112 watts to heat each bedroom. A resting/sleeping occupant gives, on average, 105 watts. That means with four sleeping occupants at night, they nearly provide all the heating load for upstairs. We need another 28 watts. A cat or dog on the landing would cover that!

It’s always great to see the results when designing systems like this, but even we are impressed with how well it’s working.

The system has another added benefit to its bow as well: cooling. We can do this in two ways: ambient air cooling and active with the heat pump in reverse. In ambient mode, it looks at the outdoor temperature, and if it is lower than the indoor temperature, it will purge the building with cooler air from outside and discharge the hot air by opening the MVHR bypass. In active mode, we can provide up to 6Kw of cooling in the summer by reversing the heat pump. This is distributed evenly through the MVHR ductwork throughout the building. Also, we can cool the floor slightly with the underfloor heating.

With the added benefit of PV on the roof, the generation will give them enough energy to run the cooling for free. We carried out this project over around 10 months on varying site visits.

And finally, tell us what the end result was for your customer?

This project looks like the best-performing system we have ever designed and installed. Our monitor tool shows that heating runs for less than two hours daily.

The last 30-day COP average has been at 850%. This is a very high result, but it’s been mild, so that we would expect this. We need to monitor it over the entire year to get an overall performance result. We are hoping for around 600% efficiency combined.

The MVHR is 94% efficient, which we can see by the monitoring tool. It recovered over 1200Kwh of energy in the last eight weeks, with a running consumption of 54 kWh. That’s a massive energy saving of 1,150 Kwh or 20 Kwh daily!

The system will save the client money without a doubt. It’s early days to show how much, as they only moved four weeks ago.

Early reports from the client show that the average energy consumption for the entire home is between 6 and 12 kWh of electrical energy per day; this is for a family of four, for the whole house’s lighting, washing, heating, hot water, and ventilation. As it is all-electric, the installed PV system will contribute to generating a significant amount over the year. It’s clean energy, reducing their carbon footprint.

After a meeting on Friday with the clients, Sam and Rosie’s first impression was how efficient and comfortable the indoor space was and how little energy they were using. I commented that they have worked hard to get a great family home and have played a big part in the outcome. We couldn’t be happier with the comments; they have been a pleasure to work for.

Lastly, it’s been a team effort. I couldn’t be prouder of how much Cameron, our lead engineer and our new apprentice, Harry, have played in delivering this project. Their skills are improving all the time. It may be my name on the door, but I could not do it without the team we are creating.