Wet underfloor heating

Gazthesparky · Aug 27, 2017

I have had a customer who has contacted me asking to look at installing a separate nest thermostat to there underfloor heating.

Currently they say they have 1 thermostat that controls the heating system and another controller controlling the underfloor heating.

They say that the radiators come on even though the the nest is satisfied. Need a site visit but looking for advice from anyone with more knowagable.

I am guessing that the underfloor is like a normal heating zone with a zone valve the nest would control the times and then the boiler firing wire goes to the boiler.

Or is underfloor heating different ?

The customer is looking for his original nest stat to control the radiators and hot water and a new nest stat to control his underfloor heating.

I guess that there are individual stats controlling the different actuator valves and hence the individual rooms.

The nest stat would control the main programming/timer of the underfloor heating and the other room stats control the activators.

The customer says he has a John guest Aura controller

Do the stats and activators go back to the aura controller and does this need to be kept ?

Should there be a time clock that controls the underfloor heating on times that then switches the aura controller ?

I need to do a site visit but looking for a bit of advice things to check for as I haven't done much underfloor heating

Cheers

Devonchris · Aug 28, 2017

Over 24 hours and no replies. I'm worried that you may be on -site tomorrow so here's my take on it, for what it's worth.

Your interpretation of how it should all work together is correct, however there are important differences to a simply radiator. Not least the temperature limit control and blending valves. Imagine trying to walk on a radiator or placing a baby on the floor that can get too hot.

This info from the john guest website, if you've not seen it already, may be of help.

Good luck. I'm sure it will all be straight forward when you get sight of the system.

Controls
As with all heating systems, suitable controls are required to achieve comfort condition, maintain economic operation and to comply with Building Regulations and British Standards.

Underfloor heating systems can be used as the sole heating system or be linked to other appliances such as radiators.

There are many ways to control an underfloor heating system and almost any boiler can be used including combination and condensing types. Manufacturers’ installation advice should be sought on specific boilers.

Whilst UFH has many advantages over traditional systems they are not quite as responsive. As they are most efficient in constant operation, it is good practice to provide controls which can “set-back” the temperature in an area by 4 – 5°C during periods of low demand such as night time rather than turning the system completely off.

Normally, room thermostats are used to control the actuator valves on the Speedfit manifold, these in turn control the flow of water in each loop.

Controls can be split into 3 main categories:

1. Flow Temperature Controls
Unless a condensing boiler with a low temperature control is being used, for most underfloor heating systems the water temperature from the boiler, normally 82°C, is reduced to the required temperature using a mixing valve.

More advanced controllers, called weather compensators, use an external sensor and programmer to adjust flow and temperature to compensate for outside conditions.

It is important to have a device to control the boiler and pump to prevent flow temperature exceeding safety limits. The Speedfit Pump Pack is fitted with an integral limit thermostat.

2. Comfort Controls
Room thermostats are used to control the air temperature in a room or area and are wired back to the control centre to enable individual pipe circuits to be opened or closed and to turn the pump/boiler on or off as required. Rooms can be controlled individually or in zones of 2 or more rooms.

There are a wide variety of room thermostats suitable for underfloor heating systems. These include electro mechanical, digital and programmable. Models can be hard-wired or controlled by radio frequency.

All types of controls are suitable for connection to the Speedfit Control Centre.

Programmable Room Thermostats offer total control of the UFH system. Each zone or room can be set with its own requirement and individual occupation patterns can be taken into account. These types of stats also offer the ability to use a “set-back” mode for maximum efficiency.

As most control systems operate with 240v power, for control in a wet area such as a shower or bathroom we recommend the use of a remote sensor or slaving from another room.

3. Boiler and pump controls
The UK Building Regulations require a link between the control systems and the boiler to ensure that the boiler does not operate when no heat has been demanded from the system. The Speedfit Controller has provision for this connection.

To discuss the options for individual projects, please contact the Speedfit Technical Help Desk on 01895 425333