proposed article for approval and criticism

Aidan (UK)

Do we really need that high tech device?


· Outdoor re-set has been around for a long time. It probably started life in commercial systems in which, for example, you may have one high-temperature primary heating system serving numerous secondary circuits for air handlers, indirect DHW heaters and LTHW radiant space heating systems. In this (commercial) application, outdoor re-set would be a practical technique for controlling the reduced secondary flow temperatures to the LTHW radiant heating systems.

Do you need outdoor re-set for a residential heating system?

· As they’re fond of saying on this forum, that depends. It’s not essential. There are lots of constant flow temperature heating systems, controlled only by thermostats, that maintain adequate levels of comfort. It’s up to the designer/specifier to consider the advantages and disadvantages, including the additional capital costs of the control devices and the anticipated energy savings, and then to use his/her experience to recommend a system that meets the customer’s expectations of comfort, cost and efficiency.

· The energy savings will come from both the reduced heat losses from the distribution pipework and, with boiler re-set, the boiler(s). Used in conjunction with a condensing boiler, a boiler re-set system will give a reduced return temperature and so increased combustion efficiency.

· Outdoor re-set on it’s own won’t maintain a constant space temperature. It responds to the outside air temperature; it doesn’t respond to wind, infiltration losses, ventilation losses, solar gains or heat gains within the heated space. For close control, the space temperature needs to be controlled by an indoor device, such as a TRV, a thermostat or a temperature sensor. An electronic control system (DDC/BMS) using thermistor temperature sensors and PID controls can react to a 0.1 degC variation in sensor temperature. Such a system may not presently be practical for domestic installations, but the price of the electronics is falling; one day soon.

· Ten or fifteen years ago, our car engines had carburettors, the ignition timing was controlled by contact breakers with the ignition advance/retard adjusted by vacuum or centrifugal mechanical devices. Due to regulations intended to reduce emissions and fuel consumption, we’re now driving cars with fuel injection, ECUs, air and coolant temperature sensors, air mass flow meters, CATs, lambda sensors, etc..

Such technology is now obligatory for a car with a 50kW engine, which may be used for a total equivalent of 20 days per year (say 12,000 miles at 25 mph). How long will it be before similar electronic technology is obligatory for 25 kW domestic boilers, which might be in operation for 6 months per year?

· Condensing boilers, outdoor re-set, immersion temperature sensors, space temperature sensors, proportional valves, flue gas CO sensors, PIR occupancy detectors and domestic electronic control centers are the way we’re heading. You may not like it, but you won’t stop it.

PJO_2

Did I miss something?

Wallies,

I've been away for a few days. Did this thread get deleted after lots of posts came to my e-mail or can I simply not find it?

I hope it didn't get so ugly that Father Dan had to step in...I have a reply to Alex ready and waiting about his "velocity" statement he responded to me.

And to think my "Learning From Kids" tried to lighten things up :-)

Take Care, PJO

Firedragon_4

It was deleted for content!!!!

Richard Miller_2

...

I didn't see any that were that bad... but it was quickly headed that way. I support it "going away". I aplogize that my posts were most likely partly at fault.