Instantaneous Hot Water – What are the Options

The demand for instantaneous hot water solutions is growing with the change in modern lifestyles and the move towards energy savings measures.

Firstly, the term instantaneous hot water solutions is a little debateable. For some its simply ensuring there is always hot water available when they need it. 

Others are looking for a hot water solution that can ensure hot water no matter what the demand, such as in hotels or leisure centres. Whilst some are viewing instantaneous hot water as tankless solutions that deliver hot water on demand.

Whatever your requirements, here is our quick guide to instantaneous hot water.

Instantaneous Hot Water - Vented and Unvented Hot Water Cylinders

So possibly not your first thought when you think about instantaneous hot water, but the fact of the matter remains, hot water cylinders can be designed to provide all your hot water needs and if sized correctly the hot water is always there for instant demand.

The challenge is to get the perfect balance of the optimum capacity, the heat source, the heat recovery time, the heat losses and the running costs.

We are seeing a growing number of enquiries from housing developers, particularly in city centre locations, looking to incorporate a hot water cylinder or cube with much smaller capacities, purely to supply sinks and basins, using electric power showers for more demand.

PROS: Huge range of sizes and capacities available, Manufactured to best suit the installation space.
CONS: Require re-heat time.

Thermal Stores

Thermal stores use a different method of delivering hot water to traditional cylinders. So rather than heating the stored water which is then called off by turning on a tap, a thermal store uses the stored water to heat the cold water as it passes through a Secondary water coil or an external PHE.

By having hot water in the coil at all times, they can enjoy instantaneous hot water throughout the day and night.

PROS: Mains pressure hot water. Multiple fuel sources. Virtually Zero Maintenance
CONS: Higher standing temperature

Plate Heat Exchanger

Plate Heat Exchangers (PHE) uses tightly packed metal plates brazed or gasketed together.  These have small channels where the Primary (boiler) water passes on one side and the Secondary (tap) water on the other side. The heat transfer process from the plates to the water is extremely fast due to the comparatively large surface area, providing hot water exactly when you need it.

PROS: Doesn’t require stored hot water
CONS: More Boiler kW input required. Flow limited to what the PHE will deliver. No Immersion back up

Plate Heat Exchanger & Buffer

The Plate Heat Exchanger (PHE) feeds via a buffer vessel, rather than directly to the hot water taps.  Hot water is always available but this allows for less boiler input - which is sized on a much smaller steady demand which the PHE can cope with.  At peak demand times, the buffer delivers the additional water required.  This is ideal for the likes of hotels, sports facilities, schools etc where often the demand is quite small other than at certain times.  For example a sports pavilion when everyone jumps in the shower after a match.

PROS: Less kW Boiler input required.  Reassurance of having a buffer of stored water.  Immersion Back-up.  Reduced legionella risk as water always circulating round the PHE
CONS: More Boiler kW input required. Flow limited to what PHE will deliver. No Immersion back up

Instantaneous Hot Water - Electric Under Sink Water Heaters

Electric Under sink water heaters are commonly used in studio apartments, retirement homes and small commercial offices, where the demand is relatively low and can be met with small electric hot water tanks.

They tend to use either 3 or 6kW of Immersion to heat the stored water

PROS: Less stored water to be heated.  Smaller space utilised.
CONS: Limited Capacity

Electric Over Sink Water Heaters

Very similar to under sink heaters, over sink systems provide a relatively small capacity heated by an electric immersion/s to provide facilities where there is generally very low demand. These can be Vented with an incorporated cold storage cistern with a feed ballvalve and float.  Commonly used in workshops, small washrooms and outbuildings.

PROS:  Less stored water to be heated.  Smaller space to be utilised.
CONS: Limited Capacity

Combi Boilers

The combination boiler was once seen by many as the perfect solution to provide central heating and hot water requirements.  By incorporating a plate heat exchanger into the boiler unit, the system can provide semi-instant hot water without the need for hot water storage.

PROS: No stored water requirement.
CONS: Poor Flow rates particularly in the winter. No Immersion Back-up. 

What’s the Difference between Instantenous Hot Water and Semi Instantaneous Hot Water?

Instantaneous hot water provides a steady continuous supply of hot water whereas, semi instantaneous hot water has limited storage but contains a heating element which can respond quickly to demand. 

For further information on instantaneous hot water and your business requirements, please contact our sales team on 01592 611123.

McDonald Engineers: Instantaneous hot water solutions across the UK and Ireland.