At our church, one of the things I've done is sort out the heating wiring (as best I can for now). The schematic is as shown below.
The theory that had me arrive at this goes :
Previously, when the wall stats was satisfied, the pump stopped along with the boiler. As we have a number of fan-coils, they quickly ran out of heat in their small water volume, and the place would go cold quite quickly. By adding pump over-run, the water still flows, the fan coils (if still on) can put out heat, and we use the stored heat in (by my guestimate) about 100 gallons of water until the wall stats brings the boiler back on again.
When I first got involved, there was a frost stat, but thankfully it didn't work as it was wired to simply bypass the timer and wall stats - thus heating the church all the time the air temperature outside was very low. It's a "big barn with lots of single glazing and gaps" so takes a considerable amount of oil to heat it.
So as well as replacing the frost stat, I added a pipe stat so the boiler would only run until the pipes are lukewarm - not enough to turn on the fan coils (now I've changed their pipe stats to a higher temperature) or to put too much heat out through the old "massive pipes" radiator system. By running the pump more than it perhaps needs to, it minimises the risk of any cold spots in the system - the stats can only measure the temperatures at single points.
![[ElectriciansForums.net] Suggestions for frost protection stats](https://electricians.s3.eu-west-1.amazonaws.com/data/attachments/65/65220-90a3acd20b94f24eacafa2bb293c25b3.jpg "[ElectriciansForums.net] Suggestions for frost protection stats")
But there is a problem. Both the frost and pipe stats (Honeywell T4360 frost stat, L641B pipe stat) operate at too high temperatures and thus we burn more oil than is needed. Both are turned down to minimum.
From memory, I've seen the frost stat demanding when my car had told me it was 8˚C outside - and it's in the boiler room so should be a bit warmer than outside anyway). That in itself isn't too bad as it simply turns the pump on, and while it can burn through lecky, it's not half as bad as running the oil burner when it's not needed. Spec says "3 to 20°C setpoint range".
The pipe stat is a problem. It turns on at 10˚C and doesn't turn off until it reaches 20˚C - which means it's running the system warmer and for longer than is needed. The spec said (seems to have gone off their site now) "L641B1004 Controller, setting 10 to 40 ̊C, min. setting 2°C"
I did try having a conversation with Honeywell, but the response I got from them was basically "not wired right, wire it this way" while totally ignoring the actual issues, and I never got any further replies from them. It was obvious that I was dealing with someone who could only look at they examples, see that my wiring didn't match, so couldn't cope with any further discussion - you can tell it's going to be interesting when somsone doesn't see any reason you might not want to backfeed a control circuit
Neither of the stats is shown as having an accelerator heater according to their spec sheets, so it shouldn't matter which way through them the current flows.
So, anyone else had similar issues ? How did you deal with it ? Does anyone make stats that work as advertised ?
A few more ramblings on the design.
As an engineer rather than just a "wiring by numbers" person, it "just isn't right" to backfeed a circuit when it's avoidable. Apart from that, at some point I want to alter the time clock & wall stat arrangement - and when I figure out access routes, I will probably power (or at least control) the fan coils from the timer/wall stat section. By not backfeeding the controls, that avoids having the frost protection turn on the fan coil fans - without needing am extra relay to isolate them.
The theory that had me arrive at this goes :
Previously, when the wall stats was satisfied, the pump stopped along with the boiler. As we have a number of fan-coils, they quickly ran out of heat in their small water volume, and the place would go cold quite quickly. By adding pump over-run, the water still flows, the fan coils (if still on) can put out heat, and we use the stored heat in (by my guestimate) about 100 gallons of water until the wall stats brings the boiler back on again.
When I first got involved, there was a frost stat, but thankfully it didn't work as it was wired to simply bypass the timer and wall stats - thus heating the church all the time the air temperature outside was very low. It's a "big barn with lots of single glazing and gaps" so takes a considerable amount of oil to heat it.
So as well as replacing the frost stat, I added a pipe stat so the boiler would only run until the pipes are lukewarm - not enough to turn on the fan coils (now I've changed their pipe stats to a higher temperature) or to put too much heat out through the old "massive pipes" radiator system. By running the pump more than it perhaps needs to, it minimises the risk of any cold spots in the system - the stats can only measure the temperatures at single points.
But there is a problem. Both the frost and pipe stats (Honeywell T4360 frost stat, L641B pipe stat) operate at too high temperatures and thus we burn more oil than is needed. Both are turned down to minimum.
From memory, I've seen the frost stat demanding when my car had told me it was 8˚C outside - and it's in the boiler room so should be a bit warmer than outside anyway). That in itself isn't too bad as it simply turns the pump on, and while it can burn through lecky, it's not half as bad as running the oil burner when it's not needed. Spec says "3 to 20°C setpoint range".
The pipe stat is a problem. It turns on at 10˚C and doesn't turn off until it reaches 20˚C - which means it's running the system warmer and for longer than is needed. The spec said (seems to have gone off their site now) "L641B1004 Controller, setting 10 to 40 ̊C, min. setting 2°C"
I did try having a conversation with Honeywell, but the response I got from them was basically "not wired right, wire it this way" while totally ignoring the actual issues, and I never got any further replies from them. It was obvious that I was dealing with someone who could only look at they examples, see that my wiring didn't match, so couldn't cope with any further discussion - you can tell it's going to be interesting when somsone doesn't see any reason you might not want to backfeed a control circuit
Neither of the stats is shown as having an accelerator heater according to their spec sheets, so it shouldn't matter which way through them the current flows.So, anyone else had similar issues ? How did you deal with it ? Does anyone make stats that work as advertised ?
A few more ramblings on the design.
As an engineer rather than just a "wiring by numbers" person, it "just isn't right" to backfeed a circuit when it's avoidable. Apart from that, at some point I want to alter the time clock & wall stat arrangement - and when I figure out access routes, I will probably power (or at least control) the fan coils from the timer/wall stat section. By not backfeeding the controls, that avoids having the frost protection turn on the fan coil fans - without needing am extra relay to isolate them.
