Central heating Q

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On Wed, 30 Jul 2003 17:22:21 +0100, "Christian McArdle"

The Alpha doesn't stop and start of its own accord, it simply winds down to a lower power with increasing resistance. The purpose of the flow switch would have to be to detect when TRVs had closed to a sufficient point that an automatic valve on a bypass opens - i.e. flow starts through the bypass and the switch operates.
This would need a relay, since the logic is wrong, and also I wonder how the bypass needed for the boiler would work. That would need an extra time switch or relays to work properly I think since it needs to run uncondtionally vis-a-vis what the CH is doing.
.andy
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I was informed by a Grundfos rep when they first came out that is stopped. Maybe he didn't know too much as it was a brand new product.

An auto by-pass would not be opened by an Alpha. The valve requires pump pressure to open it. When the Alpha detects pressure it reduced the speed thinking TRVs are cloosed down. A permanent by-pass is the best option. The flow switch detecting if the TRVs are closed should not be in the circuit of the by-pass.

A flow switch would switch off the boiler/burner, maybe via thermostat terminals. The Alpha can be left to run as
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Possibly it did to begin with. I have one for my workshop circuit and it definitely doesn't stop, although it it does drop power level considerably. I tested it using the ball valves that I have to isolate it.
One thing that it does do is to pulse a few times when starting. Apparently this is to help clear any accumulated air.

bottom end setting.

The trouble is that flow switches (apart from expensive industrial process control ones) are not that accurate in terms of operating at a certain rate. They tend to be either a gravity or spring assisted mechanism. I have one on the secondary side of my workshop circuit. The pump is located in the workshop and operated by a thermostat. When water flows, the flow switch detects it and operates a 2 port zone valve to the primary side of the heat exchanger, and of course fires up the boiler. This way, I don't need any electrical control signals between the locations.

.andy
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How slow does it get to? If it is very slow pumping nothing it is probably OK.

If that is the case then all soved by inserting an auto by-pass. The pump just keeps turning until a TVR opens up, the the auyto by-pass will slowly close.

The unit sold by DPS uses a magnetic switch. They are quite accurate in detecting 2 litres flow per min. I have used them and they are fine.

A pipe stat detecting heat?

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I haven't measured it, but the pump certainly backs right off as the flow is restricted by closing the valve. The data sheet says that the minimum level is around 0.4 cu.m/hr

This is what I'm using, although I did have an issue with DPS. They originally sent a duff one that had obviously been used before in something. Admittedly they did immediately send a new replacement, but I don't appreciate receiving secondhand items. I am not sure that I would do business with them again.
The switch is certainly sensitive so does its job as I require it. However, it has no form of adjustment, so in an application where the need was to control something based on a specific flow rate I am not sure how successful it would be. Also, if the switch were used to control the pump, you would create positive feedback. The switch operates to stop the pump when the flow stops. However when the flow does stop the switch operates again and the pump starts. Some form of logic using relays such that the flow switch triggers the pump going off and it stays off until some other event starts it again. Something like the thermostat causing heat demand might have to be the means to reset everything.

No, the logic is the other way round. The thermostat in the workshop is a room type . In fact I did rather well. I happened to be in Homebase one day (I don't normally use them because of their poor customer service) and they had a table of clearance items. I picked up a Landis & Staefa REV100 controller with time setting, set back, proportional control and LCD touch screen for 12. List price is nearly 100. There's even a set of auxiliary switch contacts so that you can override the heating to off. Apparently the Germans use this feature connected to a window switch so that when they take the bedclothes and hang them over the balcony rail of the apartment in the morning, leaving the window open, the heating is cut off. For me it's ideal because I can automatically turn off the heating when I open the door of the workshop for any length of time.
The controller simply turns the pump in the workshop on and off as required. This causes water to flow in the secondary circuit. This is picked up by the flow switch in the house and that in turn operates the motorised valve controlling flow from the primary circuit through the heat exchanger.
It works quite effectively. Ultimately I'll tie it in to the rest of the house system probably using some form of RF telemetry.
.andy
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Not "best" practice, but probably the most common one, and compliant with Part L. The regs seem to suggest you have to have independent control of living and sleeping areas. It suggests that TRVs, room thermostats or other devices can be used to achieve this. It doesn't say what method is best.
The "best" method that is easy to make from commonly available parts is to zone off each room and have each have its own programmer/thermostat so that each room can have its own time and temperature settings. (i.e. dining room could be set to run on boost only before you eat (unless you eat religiously at the same time every day), bedrooms off until 9pm, then warm, but getting progressively colder through the night etc). Not a TRV in sight in such a system. Outside temperature compensation is good too, if it can be made to work with a multizone system.
The absolute best system would have analogue temperature sensors in each room, an analogue outside temperature sensor, analogue valve actuators on each radiator, analogue power request signal to the boiler and pump, analogue sensors on the flow and return lines, and a little computer box to take the inputs, compare with your required temperature profiles for each room and drive the actuators, boiler and pump as required by a very complicated set of algorithms (probably neural net based learning type) that predict temperature changes, pre-empt required temperature changes, prevent boiler cycling and keep each room precisely at its individually selected temperature, within the capability of the system to do so.
Christian.
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On Wed, 30 Jul 2003 16:25:10 +0100, "Christian McArdle"

I'm in the middle of implementing just such an arrangement of controls. It's helpful to be able to take data from the boiler to determine what it is doing, since I want to take advantage of its capabilities rather than fighting them.
The algorithms are certainly the most complex part, especially when you have rooms used quite variably.
Temperature sensing is very easy as is the analogue valve actuating part.
.andy
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Polyplumb and Speedfit use the Grundfos Alpha in their UFH systems. When all the zones are closed by electric actuators the pump is still running. The pump clearly can pump against a total stop when wound down to its minimum speed without any adverse affects. Having an auto by-pass valve or a fixed by-pass will make no difference. Just insert a flow switch on the return and all rads can have TRVs and no electric room stat.
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Good advice. I took a radiator off, turned the TRV off (as I thought) and went away for Christmas. Cold snap, TRV opens, new wood floor flooded. Not a Happy New Year. :-(
Rob
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