Wanting to reduce gas usage - New Heating Design Circuit - will it work?

2nd_time_buyer

I expect there are good reasons for you not going down the heat pump route. But, hypothetically in a well insulated house, with a thick slab and UFH, would it be possible to only run a pump during solar/Go periods?

Reed_Richards

UFH has a very slow repsonse time so is il-suited to being run "hard" for a limited period of time.  Large radiators would be better if you don't mind being lightly simmered in the middle of the night.

polocanthus

I am planning a very simple heating system: 7 copper cylinders each 160 litres = 1120 litres with 4 immersion heaters and a circulation pump during heating; water pumped through mixer valve to underfloor heating. 

Static pressure is only 0.3 bar, so unvented, 80 litre expansion tank. Emergency pressure/temperature relief valve for low pressure seems unavailable. 

Hot water dealt with by separate systems. 

2nd_time_buyer

Reed_Richards said:

UFH has a very slow repsonse time so is il-suited to being run "hard" for a limited period of time.  Large radiators would be better if you don't mind being lightly simmered in the middle of the night.

Isn't a slow response time what you need e.g. heated during the night, then radiating during the day? If it was too slow, could you "idle" it during the day to maintain the slab temp?

michaels

polocanthus said:

I am planning a very simple heating system: 7 copper cylinders each 160 litres = 1120 litres with 4 immersion heaters and a circulation pump during heating; water pumped through mixer valve to underfloor heating. 

Static pressure is only 0.3 bar, so unvented, 80 litre expansion tank. Emergency pressure/temperature relief valve for low pressure seems unavailable. 

Hot water dealt with by separate systems. 

What is your planned temperature range - I calculate 40kwh storage with temp between 50 and 80 degrees (assume min 50 for heating circuit but perhaps you can go lower with UFH?).  Obviously at 12kw you can fill the storage easily in a 4-hour cheap electricity window.

What sort of losses will you get from the cylinders, or will that be useful heat?

Freepost

Reed_Richards said:

I'm late to this conversation but I have a pumped loop feeding my hot taps so I can give you some observations.

1. I run the pump for 5 minutes every hour except when we are asleep.  This keeps the water in the loop adequately hot except in the middle of the night.
2. It took a bit of searching to find a timer that would allow me to run the pump 17 times a day for 5 minutes each time.  Electromechanical timers did not work properly but I eventually found an electronic one.
3. My loop splits in two so each half has a valve on the return which shuts down the flow once it reaches a certain temperature (being the temperature which I want my water to be).
4. My circulation pump (later on the return) also cuts the flow once the water passing though it reaches a certain temperature.  This is belt and braces.
5. In my case the flow is the output from the cylinder and the return goes to the secondary return port on the cylinder.  There is a TMV on the output.  This is not the ideal plumbing arrangement but it works except in summer.
6. In summer the tank can get very hot, 65 C or a bit more, because I heat it with spare solar power.  In principle this could lead to a scalding risk because the hot water won't get mixed until a tap is open so the loop might fill with scalding water.  What actually happens is that loop fails to circulate anything more than tepid water.  This is less than ideal but in summer you don't mind so much.  I presume this happens because the TMV can't cope so just shuts down the flow.   

Hi Reed,

I was looking at the Lowara Ecocirc Pro 15-1/110U pump, it has a built in timer. Unfortunately it only has a 1m head so I think it would struggle getting to the first floor. The 3m head version doesn't have the timer but it's the version that I will purchase and just add a cheap digital timer to it.

What valve are you using for temperature sensing?

You mentioned the UFH in your later post, whereas my drawing shows the central heating system splitting between Rads and UFH. The UFH has its own manifold and blending valves/motor etc. Sorry for the confusion.

F.

(editted because keyboard messed up and can't spell .... need to get a keyboard with better literacy skills)

Freepost

Hi,

I have changed the design a little, I was finding the cost of Plate Heat Exchangers prohibitive, this was largely true due to the power output which was up rated to 165kW following discussions at https://www.plumbersforums.net/threads/t50-on-new-install.121196/.

I'm not saying that the 165kW PHE was the way to go, just looking at the info available from a working system but as I say 165kW PHE are expensive consequently I have gone in a similar direction to Solarchaser and purchased a cylinder with an additional coil for the DHW, the cylinder will provide the Central Heating directly.

F.

michaels

Will you use a mixer valve on the rad circuit to control the temp as otherwise it is straight out of the top of the tank?

polocanthus

Hi Michaels 
Underfloor heating is at 35 degrees at the moment. Adjusted manually as high as 50 degrees when really cold. 

A gradual fall in temperature in the evening is probably a good thing.

Tanks will be well insulated. 

I am considering a separate water heater to avoid unvented tank pressure and temperature relief valve problems. 

But then I will have problems with the water heater trying to be intelligent. Maybe I should just vent it.   

70sbudgie

Seeing @Freepost's latest drawing has made me wonder if I could utilise the second (currently not connected) coil in my hot water tank for my ufh? My gut feel is that there are plenty of reasons not to, but I can't think of them. 

My hw tank is currently plumbed the traditional way.