Another Heating Question

[David Wallis]

I currently have an oil fired boiler that I can control via two DMX relays - one for hot water and one for heating.

Currently this is done via a schedule only. (i ripped out the old timer and thermostat)

I'm in the process of adding 1 wire temp sensors to each room so I can get some data out (this is only temporary as the house is almost going to get knocked down for the refurb - but want to get the controls correct whilst I can play and have time!)

I do not have valve actuators currently - just trv's

Whats the best way of controlling this, just adding IRC's to each room that has a temp sensor and then taking the output of each IRC and turning the boiler on if any of them demand heat and let the TRV's deal with the rest?

David

[Duncan]

no its not going to work very well

the problem you will have is that an IRC could make heat demand but the trv be mostly closed, leaving the boiler firing against closed valves

due to differences between the temp sensors and the trv and the IRC heating up period, the chances of the IRC calling for heat exactly when the trvs are open is extremely low, leading to inefficiency and the system pump working overtime, possibly with cavitation and excess noise and wear.

your system should have a system bypass to allow for this situation, but what you are proposing is likely to make things worse.

[David Wallis]

The boiler wouldnt fire against closed valves as there are towel rads without trv's on them.

[Duncan]

thats fine - you can build a system ready for go live

temp sensor and IRC for each room/zone, each linked to its respective actuator valve (radiator or ufh manifold)

IRC outputs are connected either by a ITC (integrated OR, heating curve) and its output linked to your boiler relay and pumps/zone valves where necessary 

or manually ORd and linked to a separate heating curve (if desired) then onto your relay for boiler/pump/zone valves

depending on your plumbing, you may need one of the above per manifold/floor

the differences between ITC and manual setup are:

ITC the links between IRCs are invisible so keep your config file less cluttered, and its heating curve changes its temperature according to the heat demand, based on the m2 setting for each room

a manual setup has memory flags linked to the OR for boiler/pump/zone valves, and a manual heating curve is not affected by the number of zones demanding heat.

a heat curve is only relevant where you can adjust the temperature of water supply to your heating devices to compensate for external temperature (eg mixing valve for ufh or output of a buffer tank) or if you are planning to adjust the boiler temperature

 adjusting boiler temperature with a manifold system is pointless as the manifold is thermostatic and always mixes down the water temperature anyway so boiler control is a waste of time

if you have hot water storage you need to keep the boiler hot enough to keep the hot water at 60degC or higher to stop legionella

boiler temperature control is dependent on having an interface you can control from loxone - usually these are proprietry and quite expensive

however, if you have an instant hot water system and a non-thermostatic ufh manifold or radiators, you can use boiler temperature control as your main weather compensation as it will not be fighting any other thermostatic control systems.

if you are planning to keep radiators for your refurb its worth looking at the sizing for radiators - usually they are rated at a water temperature of around 75 deg - the boiler is less likely to be in condensing mode, there is a risk of burns and also overshoot - if you resize the rads for a working temperature of between 40-55 degrees there will be an increase in efficiency with a condensing boiler, less burns risk and less chance of overshoot of the room temperatures.