Ed Morris, Technical Manager at Altecnic, investigates what makes a ‘modern’ Heat Interface Unit (HIU) as their popularity increases as a solution for multi-occupancy builds.
Modern Heat Interface Units (HIUs) boast an impressive array of ‘smart’ features that provide close control of heat output and energy use. This is helping to fuel a steady increase in the market, and according to the data from the recent World Heating Report, around 38300 HIUs were installed in the UK, of which the large majority was fitted in buildings served by central plant systems. The market had already grown by 4% in 2016.
HIUs provide control centralisation and metering point at each dwelling. Ease of accessibility, either inside or outside the property, makes the meter reading ideal for energy providers, as well as saving time. Additionally, the space requirements for a unit is optimal when compared to a combi boiler’s space requirement.
Primary flow rate limitation protects the network from failure caused by poor apartment heating control, high start-up demand and ensures reduced demand peaks.
Return Temperature Limitation (RTL): The HIU automatically controls output (heating and DHW) to hold a configurable low return temperature. Ensuring network efficiency, even if the radiators are poorly balanced.
Smart controls for HIUs
A configurable integral room controller can be set up to customise the level of access and features that the tenant is allowed to use. Compatible with smart controllers such as ‘Nest’, ‘Hive’, etc. it can be set to on, off or timed to come on only when the tenant requires, saving energy and cost for the tenant and the network. Each HIU can be configured individually or globally remotely via the BMS or MODbus network.
Typical UK apartments have a heating demand around 3-4 kW. However, for the first time in 10-15 minutes of the heating coming on, the apartment can take up to 8 or 9 kW from the network. If a large number of apartments are on heating at the same time, say at 7am on a weekday morning, then the network may not have enough capacity and it will fail to provide hot water at the extremities.
Some HIUs have the facility to set a maximum flow rate a HIU can take from a network. A HIU connected to a 3 kW apartment can only take 3 kW, nothing more, therefore the network is protected from failure and its demand peaks are reduced.
The low heating demand in today’s apartments mean that only a very small flow rate is required on the heating circuit. This low flow rate makes it very difficult to balance the radiators in the apartment.
The result is that most apartment heating systems are not balanced correctly, and the return temperature will be high and subsequently transferred to the network and the efficiency of the whole network will be greatly reduced.
Many HIUs are equipped with Return Temperature Limitation (RTL), which allows the installer to maximise return temperature on the networks. Once enabled, the HIU will control its output into the apartment to ensure that this pre-set, primary return temperature is met.
Many HIUs on the market have a permanent, built-in pre-heat function. This blends energy through the HIU constantly 24 hours a day. Bearing in mind that the tenant may only use their hot water a few times a day, having preheat on permanently makes no sense and costs the tenant money. The configurable controller can be set to allow the tenant to set the preheat function, just like their heating system, to come on and go off automatically only when required.
A HIU with a full MODbus output/input can be set up and commissioned remotely. Any faults or error message on the HIU can be read remotely. If a tenant believes there is a fault with the HIU, the unit can be interrogated remotely and the faut van be diagnosed prior to any attendance on site. The engineer can then ensure the trust that they have gotten the correct spare parts required prior to going onsite. Even the actual temperature within the apartment can be checked to see if it is at the set point set on the HIU.
HIUs and efficiency
The drive to make buildings ‘smart’ continues apace and there are now companies that specialise in the operation and running of these smart buildings. The MODbus output from the HIU removes much of the hardware that needs to be installed on a smart network and therefore cost. The MODbus allows more accurate network control based on demand and the HIU facilitates a much more efficient network.
Another feature of some HIUs is the weather compensation option. The HIU has the ability to vary the heating output based on outside temperature.
A prepayment unit can also be wired into the HIU controller and, when the tenant runs out of credit, the HIU will close down the heating DHW output without the need for a separate motorised prepayment valve. This not only saves money, but also allows for prepayment to be retrospectively installed without the need for extra plumbing work.
The future of HIUs
Altecnic offer a range of modern HIUs, indirect and direct, which all have been designed to the Caleffi high quality standard.
With this, the most recent HIU released by Altecnic has been designed with heat pumps in mind. The SATK32107 achieved a VWART figure of just 28C on the low temperature tests. VWART is a measure of efficiency and details the return temperatures that would be achieved on a typical UK project when the HIU is in all its operating modes. The resultant figure shows how good the HIU is at using the available energy from the network. The lower the number, the more efficient the HIU is.
The SATK32107 also recorded a very low required annual primary flow rate of 90.71 cubic metres. This means that when in operation the SATK32107 on a low temperature network, requires less primary water than any other HIU so far tested. This reduces the amount of water circulating in the heat network reducing heat losses, energy use and carbon emissions. When looking at a typical project, the reduction in circulating water over a year can be staggering. A saving, the equivalent of 5 Olympic sized swimming pools can be achieved!
These characteristics make the SATK32107 the number one choice HIU to be used on low temperature networks, such as those lead by, or solely using heat pumps.
The full range of Altecnic HIUs can be viewed at: altecnic.co.uk/commercial/heat-networks/heat-interface-units
