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Discuss TRVs & Cost Efficiency in the USA area at PlumbersForums.net

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Hi,

I've become a bit obsessed with understanding how my heating and hot water system works. I'm a total novice but I've just become genuinely interested and have been watching loads of Youtube videos and read a book on 'Basic Plumbing' recently. It'd be good to bounce some questions off people about things I probably don't quite understand yet. My question is about how TRVs can save you money - I believe they give you the option of shutting off radiators (setting a low temperature benchmark) and restricting the amount of water in the system that needs heating. I'm just wondering how much this can equate to. If I have a house with 14 radiators and I've got a gas boiler, vented system (tank in loft, cylinder on landing, boiler in garage) and I shut off all but, say, 3 radiators. Would that equate to a 75% saving on heating costs or is it not that simple?

Nick
 
The efficiencies come from the fact that TRVs regulate the flow through the rads to maintain a fixed room temperature, with non TR valves if the ambient temp goes up, the room temp will also go up as a fixed flow is going through the rads, which could lead to you heating the room more than it needs to be and therefore wasting energy.

Re your scenario its not that simple, as the surrounding rooms would be colder, the rads in the heated rooms would have to work harder to maintain the same temperature in those rooms. Think its generally recommended that you have the rads on in all rooms to avoid major temperature variations within the property which can lead to damp/condensation problems. Just have them set to a lower number in the rooms you don't use as much.
 
I'm just wondering how much this can equate to. If I have a house with 14 radiators and I've got a gas boiler, vented system (tank in loft, cylinder on landing, boiler in garage) and I shut off all but, say, 3 radiators. Would that equate to a 75% saving on heating costs or is it not that simple?
Not that simple. Houses are quite complicated to understand because the rooms are not separated from each other by perfect insulation so the temperature and heating requirements of different rooms are not necessarily independent of each other.

Broadly speaking, the better insulated your home is the less important gadgets like TRVs are to its fuel economy. In my opinion, for a home that is not so well insulated, the basline distribution of heat should be achieved by correct sizing of radiators, correct balancing of the hydronic system and boiler control. In such a system, most TRVs are open most of the time but selectively close when solar gain reduces the heat needed for rooms on the sunny side of the house.

The problem with my 'correctly sized, correctly balanced' approach is that it is time-consuming to get right and a lot of installers rush out of the door once every radiator is nice and hot. In such systems, the TRVs take over control and compenstate for sub-optimal balance and save some engergy. Unfortunately, the side-effect of this is that in the autumn and spring when the TRVs are almost 100% closed, the boiler will short-cycle.

Heating systems are understandable once you have the full picture (sizes, losses, gains, thermal-capacities, etc.) but getting the full picture can be hard work.
 
TRVs also help to increase the condensing benefit of HE boilers as the rads can run with very low return temperatures even with relatively high boiler temperatures.
 

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