Thermal Store problem

[brackwell]

Klaus,
Can i just check something with you.  I thought the specific heat of water was 0.0017Kwh/kg C        And therefore using your figs,  15Cto 40C for 120L = 5.1 Kwh.  The immersion is only on for 1 hr say 3kwh before losses. I am at least assuming the tank is not being heated at night to be used in the morning!

Ken

[KLD]

Ken, then specific heat of water at 20°C is c=4183 J/K kg. With 3600kJ/kWh, this value becomes c=1.162e-3 kWh/K kg. 1L of water is near enough to 1kg mass.
120kg*(40-15)K*1.162e-3 kWh/K/kg = 3.48kWh
(I think your value for c may be missing one digit: 0.0017 instead of 0.00117 )

In Roy's customer's case, 170L volume, immersion on for 1hour, 3kW power: 170kg*3kWh*1.162kWh/K/kg = 15.2K temperature increase.


Klaus

[KLD]

Due to insulation I have avoided temp readings.

Roy, if the sensors for the TDC3 are mounted at the top and bottom of the tank, then you could use the readings from these two. Both are reported on the TDC3 display. A before and after reading to check how much heat the immersion puts into the tank, and whether the tank reaches high enough temperatures would be a good starting point. The 60°C setting on the immersion element 'stat might be a tat low. The TDC3 and the "top" sensor in the tank will control whether the element comes on, and the 'stat on the element switches it back off. Depending on the specific layout, what might happen is that the water heated by the element rises quickly, the top sensor / TDC3 setting becomes satisfied, and the element is switched off. Sadly, only the very top section of the store was heated, and your customer only has enough warm water for a shallow bath.

Klaus

[andito]

Roy,

First thing I'd check on a 20yr old open vented gravity sytem with no circulation would be header tank has water then check for blockage on cold feed to system. Too often I've overlooked the obvious only to pull my hair out for a couple of hours then realise I've been looking in the wrong place.

Hope I'm not trying to teach you how to suck eggs.

Andy.

[turnerroy1]

Hi all And thanks for your replies. I now have all the readings from the TDC. Here goes.
T min S1 15 deg
T max S2 60 deg
Delta TR1 5/3 deg
T Set S3 60 deg
Hysteresis 5 deg
ABS R1 daily
ABS R2 off
Frost protect On
Frost level 1 6 deg
Frost level 2 3 deg
Col alarm 85 deg
SPF V1
SPF T on 105 deg
SPF T off 90 deg
Recooling on
Recooling T set 70 deg
Anti legionnaire off

Hope all of this helps any suggestions on optimising would be gratefully received.

I certainly believe the conflict between the immersion stat and TS 3 to be a factor any thoughts on a resolution ?

As Andy suggested the header on both the combi store and header on boiler were isolated on my first visit. Opened valves and got wet. Remade relevant joints and all now O/K with pressure from bleeds on rads.

Customer reports improvement on hot water but I remain unhappy. I have not traced a flap valve and am still looking to use the boiler to take up excess rather than the immersion but a combination of the two will be necessary for summer / winter due to lack of boiler controls.

Thanks all, will keep updating. Regards.

[KLD]

Roy,

Interesting settings you found on the TDC3 there.     
For the following I assume there is a TMV fitted to the thermal store's DHW outlet (as I believe is standard for the Newark stores).
Caveat: I have no formal qualification regarding plumbing / solar installations. Just an interested physicist, and have installed my own system two years ago.

• Taken from the earlier calcs, a maximum store temperature of 60°C will not suit your customer's demand. I would change TmaxS2 to 80°C or even higher.  This only effects the solar side of things.
• I would also take the immersion off the TDC altogether, and let the build-in thermostat and timer control it. Again, raise the 'stat setting a little, say to 70°C.
• Frost protection: is there a sufficient concentration of anti-freeze in the solar loop?
• Panel Protection: is the system installed to be stagnation tolerant? (mainly panel as highest point in loop, expansion vessel of sufficient size) I'd switch the SPF off.
• Same on Re-cooling: a heat-pipe panel manifold will not result in much heatloss when re-circulating too hot water from the store at night (this is a flat plate panel thing).
• With the TmaxS2 at 60, and the number of tubes you reported, it is highly likely that the system overheats every few days in summer. The solar pump switches off at 60°C, this might be only mid-day, the panel temp quickly rises further, at 105°C the panel protection setting switches the pump back on, hopefully keeping the fluid from boiling. Doesn't sound very stable to me. You might want to search this forum for heat dumps.

So far to the TDC.

all now O/K with pressure from bleeds on rads.

Does this mean the boiler is heating the store properly now?

I have great difficulty understanding the controls of heating the store during March and May, i.e. when the central heating is still on and yet there is a high solar potential. Won't the boiler keep the store constantly at high temperature, and solar will contribute hardly anything?

Klaus

[turnerroy1]

Hi Klaus.
As previous there are no controls on the boiler input coil hence no motorised valve. Gravity feed from boiler is by convection which is not happening which is my primary problem. If I remove the immersion from stat 3 on TDC I could fit a tank stat in series with the timer at the level of stat 2 on the TDC but I can not see a significant gain. I will raise the S2 max to 80 Deg as you suggest. I am also going to confirm all stat readings with an independant thermometer into the various levels on the tank and will report back when complete. My main concern is to optimise the solar and then work back through all other heat inputs.

Thanks for your input.

[KLD]

Roy,

as I said earlier,

The TDC3 and the "top" sensor in the tank will control whether the element comes on, and the 'stat on the element switches it back off. Depending on the specific layout, what might happen is that the water heated by the element rises quickly, the top sensor / TDC3 setting becomes satisfied, and the element is switched off. Sadly, only the very top section of the store was heated, and your customer only has enough warm water for a shallow bath.

You really want to measure the temperature where it matters, ie. at the lower edge of the volume you want to heat. Using S3 at the top of the store will create problems. If the 'stat on the immersion heater works, then I can't see any benefit in having the TDC control the immersion element. (But may be I just haven't understood immersion heaters.)

Trying to optimise the solar bit in mid November is erm... optimistic.

I'd suggest you use the immersion element to determine how much heat your customer needs (heated volume and average temperature of store). This is straightforward and can be done while you further troubleshoot the boiler circuit.

Klaus

[andito]

Remade relevant joints and all now O/K with pressure from bleeds on rads.

.

Pressure at rad bleeds won't rule out blockage on gravity system pipework as if the flow (or return) is blocked or restricted the water can still pass through the return (or flow) to the rad circuit. Check accessible pipe using a strong magnet, if it drags on the copper you have a restriction/blockage which needs cleared.

I would agree with Klaus that you are rather optimistic trying to optimise the solar at this time of year. If I were in your position I would concentrate on getting the gravity working first to ensure the tank is getting to temp.

Andy.

[turnerroy1]

Hi Andito
Totally agree my problem is that only the pipework near the tank is accessable. All boxed in kitchen exists underbath 1st floor and turns into tank cupboard. I am going to try draining down and putting electricians draw wire through if this fails I will cut in and use my cable access rods. I hate multiple problem jobs and wish customers would deal with each problem as it occurs. Regards Roy

[clivejo]

Once the coil and boiler are drained, cant you blow down the pipe to test for a blockage?  It sounds like an air lock to me

[andito]

Roy,
Can you access where the cold feed & open vent pipes link into the gravity flow/return pipe? This is where I find most system blockages occur. If so check around this joint with a strong magnet, if there is a blockage with sludge you will feel some drag from the magnet. I try not to drain until I am sure if & where any blockage is as sometimes the sytem won't fill once you've drained it which doesnt go down too well as now the heating won't work either

Don't know why but customers seem to like to save problems before having them looked at making resolution more problematic.

Good luck,

Andy.

[turnerroy1]

Roy,
Can you access where the cold feed & open vent pipes link into the gravity flow/return pipe? This is where I find most system blockages occur. If so check around this joint with a strong magnet, if there is a blockage with sludge you will feel some drag from the magnet. I try not to drain until I am sure if & where any blockage is as sometimes the sytem won't fill once you've drained it which doesnt go down too well as now the heating won't work either

Don't know why but customers seem to like to save problems before having them looked at making resolution more problematic.

Good luck,

Andy.

[turnerroy1]

H Andy. Thanks for input. The 15mm feed drops straight into 28mm return so I think it is unlikely to be blocked at that point. There are valves on both flow and return (both fully open and checked) I am going to drain then cut into flow and push cold mains back through boiler and then reverse through 15mm from F&E tank all this happening on friday. I have already introduced a manual air release into flow via 15mm upstand terminating above top level of coil, so no air lock in coil. Coil fills again from F&E so on that leg no blockage. Will keep you updated. Regards Roy.

[turnerroy1]

Thanks to all who replied. The problem is now resolved. Cut 22 15 22 into both flow and return. Pushed cold main through both with drain on boiler open and F & E capped. Cut out 6 compression elbows in tank cupboard and replaced with easy bends, from bender. final flush through after connection. Gravity to tank now giving excellent service with Solar still giving 5 deg lift around lunch time. Immersion now off although I have left the facility available for possible summer use. Happy customer at last.