Understanding short cycling & UVC water temperatures?

[vulcancontinental]

Usually, this is done via an immersion heater, scheduled to operate once per week.

With most Vokera boilers there is a Legionella program

 

[dilalio]

With most Vokera boilers there is a Legionella program

Yes, on boilers but not usually possible with heat pumps. There are some that now can, but why would you need them to, apart from the weekly Legionella program... If you're all electric then best let an immersion do that.
Then again... If everything's eventually going to be leccie, might as well have a direct cylinder for all DHW.

 

[vulcancontinental]

Yes, on boilers but not usually possible with heat pumps. There are some that now can, but why would you need them to, apart from the weekly Legionella program... If you're all electric then best let an immersion do that.
Then again... If everything's eventually going to be leccie, might as well have a direct cylinder for all DHW.

I was thinking of hybrid systems where depending on the boiler it can control the heat pump from the boiler control, gas still being cheaper than electricity.

 

[Ruggers]

If you're having radiators and underfloor you'll need a system that can offer two flow temps for heating with an electronic mixer or a mechanical thermostatic blending valve for the underfloor.

Yes, DHW reheat can be done priority as the coils within are large area and give rapid reheat at high temp so short lived lack of heat to space heating is not noticed. Just like a combi.

Not sure just what a thermal store can offer that a boiler, cylinder etc cannot unless you plan to incorporate a heat pump as well.

There are Vokera boiler, heat pumps and controls that can do all this.

I had a chat with a heat engineer today about the various options. I will check with others for their opinions too. There just seems to be so many options to consider, I'm only used to combi's since removing an open vented tank a decade ago, not modern unvented systems. Whats the benefit of having a tank over a combi if your having PDHW? Is it just so you can run two showers at the same time?

I will now select a boiler with Opentherm, but not too sure about PDHW, need to know more about it & how long it takes for a tank to heat back up after having a bath or 10 minute shower?

1. Does it heat the stored water rapidly by supplying a flow matching the stored temp, or does it increase the temperature much higher for the rapid heat, ie: 60C stored has a 75C flow when in PDHW mode?
2. Can you disable PDHW if you don't like the downtime for reheats?
3. Radiator flow temps were going to be designed for 55C radiators and UFH around 45C using blending valve on UFH manifold.
4. Thermal store idea was just for ease of installation and not having to pay out a separate £100 annually for UVC services on top of the annual boiler service usually similar price. For either thermal store or UVC i'd like the option to add solar PV with battery storage or ASHP at a later date if things head in this direction. Budget doesn't allow for these at the moment when installing a gas boiler.

 

[vulcancontinental]

I had a chat with a heat engineer today about the various options. I will check with others for their opinions too. There just seems to be so many options to consider, I'm only used to combi's since removing an open vented tank a decade ago, not modern unvented systems. Whats the benefit of having a tank over a combi if your having PDHW? Is it just so you can run two showers at the same time?

I will now select a boiler with Opentherm, but not too sure about PDHW, need to know more about it & how long it takes for a tank to heat back up after having a bath or 10 minute shower?

1. Does it heat the stored water rapidly by supplying a flow matching the stored temp, or does it increase the temperature much higher for the rapid heat, ie: 60C stored has a 75C flow when in PDHW mode?
2. Can you disable PDHW if you don't like the downtime for reheats?
3. Radiator flow temps were going to be designed for 55C radiators and UFH around 45C using blending valve on UFH manifold.
4. Thermal store idea was just for ease of installation and not having to pay out a separate £100 annually for UVC services on top of the annual boiler service usually similar price. For either thermal store or UVC i'd like the option to add solar PV with battery storage or ASHP at a later date if things head in this direction. Budget doesn't allow for these at the moment when installing a gas boiler.

1: The latter. Houses lose heat slowly so reheat the cylinder quickly and prolong cooler running for space heating at lower, more efficient temperatures matching reduced space heating load.
2: Depends on the control but yes. The EPH does either but I'm sure there will be others.
3: Good but the UF will often be running lower than that. An electronic bending valve has a slight advantage I believe.
4: I've not lived with a thermal store but they get mixed reviews. Depending on the property personally I'd still go for a vented cylinder if the head is available, gravity is free and requires no servicing.

 

[Ruggers]

PDHW is something I'd have to try, it sounds good but having not used it, I need to know the reheat times to see how it would effect heating, lets say in the morning at winter if you had a shower before others were due to wake up requiring heating.

Will a shower drain a hot tank over time if a few were taken in succession or does PDHW reheat almost as quick as your using it depending on shower flow rates?

I didn't know electronic manifold blending valves existed I thought they were all thermal type. I'll look at EPH, from a quick search is it just a brand name? I have been looking at wunda trades products and continal underfloor. Wunda was a lot cheaper though.

Theres so much for and against heat store/thermal stores and it seems locally most heating engineers are familiar with UVC and a gas boiler. It was just something to consider but theres a lot to take in if it's not your trade & locals don't really fit them. Be nice to reduce the service fees. Open vented with header tanks only just doesn't offer any pressure really, max 1 bar downstairs.

 

[vulcancontinental]

Cylinders can be purchased with high or fast recovery coils minimising reheat. Also double coils for solar later and run in series from the boiler until then.

As for recovery from showers that depend on how long it lasts and the flow rate through the shower you want; is it a deluge or just get clean?

A decent head of a meter will give a good shower, does for me for 35 years and haven't even had to change a ball valve. Not fashionable but nothing comes even close in reliability. People get sickered into UV but it's a pain in a hard water area and instal and service costs are far higher. Better flow rates for sure means more expense for fuel too but you can only get so wet.

Electronic mixers will cost more but can be tied into boiler operation at low temp whereas mechanical it's more difficult. Eg the electronic can adjust if temp to suit conditions, mechanical tries to hold a design temp and that's it.

 

[Ruggers]

It was going to be solar PV rather than solar thermal if i decided to add this later on so i'd link to the immersion or whole house however it works.
It's not my main focus at the moment, solar and or ashp might never make the money back if you add too much. Does in series refer to splitting the supply to the tank into two to feed both coils? If so, the heat engineer said this won't work very well as it will reduce the flow. I honestly thought with 2 coils there would be more surface area heating the stored water.

Not a deluge & not really a fan of powerful showers, currently happy with a combi 33kw with upstairs shower, sunflower type head from the ceiling,190x190mm gives plenty of rainfall for us, not sure what my current water pressure is, probably 1.3bar on a shared mains because the boiler now won't pressurise more than that. Hot water storage tank will be on the ground floor along with the boiler.

 

[vulcancontinental]

Not sure what your heating engineer is getting at.

The position of the cylinder close to the boiler is a good thing but it's the distance of the shower rose below the CWS cistern that's important for the shower (and pipe sizing)

 

[Ruggers]

Not sure what your heating engineer is getting at.

I seen a video of a guy explaining that if your going to buy a central heating water tank, Always opt for 2 coils inside over one like a solar tank. Even if your not going to use it for solar, just get your 28 or 22mm flow from the boiler and send it to both coils so that your getting more heat put into the tank for a quicker reheat time. He just said this wouldn't work properly. Mentioned about flow and some kind of disruption to the flow or the tanks heating balance with the coils being in different positions operating at the same time where as they'd usually be running at different times for solar and gas. I can ask again when i speak next.