Brit seeking heating design help

John Aston

Hello. I am a complete plumbing novice based in the UK who has spent the last four weeks reading manufacturers' literature and piecing together a brand new heating design for my home which I am renovating. This forum has been recommended to me as a good source of impartial expertise and I wondered if you guys would kindly take a look at my idea, please?

The attached PDF drawing HD01i2 (also posted at http://tinyurl.com/5lx84 ) shows the proposed hydraulic design for a large domestic heating system. The boiler and hot water storage cylinder is on the left hand side of the drawing, space heating is on the right. (You might need to rotate the view so that the drawing is in landscape orientation in your browser). Over here in the UK, condensing boilers are the norm and will be mandatory next year. In my case, the hot water heating pipes and and space heating pipes are unvented (i.e. no header tanks).

The cylinder is located less than 25ft pipe length from the boiler so I hope that the boiler pump will get the water there on its own via a divertor valve. (The Vitodens 300 boiler that I'm considering can pump 365 gal/hour at 3 psi residual head).

Some explanatory notes on the design are appended below. Any comments would be gratefully received but my principal questions are:

(1) The internal space heating requirement when it's -3°C (27°F) outside is 31kW (106000 Btu/h). In addition, there is a 250L (66 gal.) storage cylinder serving three showers and one bath for a family of five. Is a 38kW (130000 Btu/h) boiler sufficient?

(2) I'm specifying 28mm (1¼") pipe through the water softener and up to the cylinder, 22mm (¾") for the boiler flow and return, 22mm (¾") to the hot and cold taps, and 15mm (½") everywhere else. Is that reasonable or over the top?

(3) A 22mm (¾") pipe is teed off the secondary side of the low loss header. From this 22mm (¾") pipe, I propose to tee off 15mm (½") pipe to each heating zone. What is the maximum distance between these 15mm (½") tees, and what's the maximum permissible distance from the furthest 15mm (½") tee to the header? (Keston Boilers told me that there is NO restriction!)

(4) What's the best way of incorporating two towel rails (bottom right) into the circuit so that the towel rails come on all year round when there is either a call for heat or a call for hot water?

Design:

The mains cold water supply is treated by a water softener (bottom left). The softened water is fed to a 250L (66 gal.) cylinder under pressure from an accumulator which keeps the cold water at about 2.5 bar (36 psi) and provides a high flow rate to all taps.

The water in the cylinder is heated indirectly by the primary of a 38kW (51hp) fully-modulating condensing boiler in the room below the cylinder. Hot water is circulated to the taps by means of a secondary pump. Because the system is unvented, the hot water is also at a pressure of about 2.5 bar (36 psi).

A diverter valve allows the boiler to heat the central heating system when there is no demand for heating from the cylinder. The boiler flow is diverted into a low loss header from which the distribution circuits (heating zones) are pumped. The header buffers the boiler primary control against sudden changes of flow in the distribution circuits.

The central heating system comprises both underfloor heating and radiators in all rooms (only a few rooms A-E are shown, for clarity). There are two heating zones: The kitchen and reception rooms on the ground floor are zone 1, and the upstairs bedrooms and bathrooms are zone 2. Since each zone comprises one underfloor heating system and one set of radiators, there are a total of 2 x 2 = 4 heating distribution circuits.

The underfloor heating circuits are connected to a manifold and temperature-controlled by room thermostats which operate the circuit valves. The water through the underfloor heating system is limited to 55°C (131°F) maximum by a thermostatic mixing valve at the manifold entry. The underfloor heating has a maximum output of 17kW (58000 Btu/h) and is only capable of maintaining a internal temperature of 9°C or 10°C (50°F) above the outside temperature.

The purpose of the radiators is to supplement the underfloor heating with up to 14kW (48000 Btu/h) additional heat when the external temperatures are cold. The temperature of the water pumped to the radiators is (almost) equal to the temperature in the low loss header. The boiler's primary flow temperature is a function of the outside temperature and typically falls from 70°C (160°F) to 40°C (100°F) when the outside temperature rises from 0°C (30°F) to 15°C (60°F). The radiators are switched on and off by thermostatic valves.

Every underfloor heating circuit has its own room thermostat and the circuits are terminated at a manifold which has its own local controller that sends a signal to the master controller when there is a call for underfloor heat. The master controller has provision for switching the hot water and heating off independently at user-adjustable times.

The system has a distribution of drain cocks and isolation valves to simply maintenance.

Sources of information:

Viessmann http://tinyurl.com/6cqtt (Page 41)

Geminox http://tinyurl.com/5glxs (Bottom of page 7)

MAN Heiztechnik http://tinyurl.com/3vzwz (Page 27)

Weezbo

*~/:) i spy at least3 minor technicalities with my eye ....

on the potable water alone....i have to dash off at the momment. outside hose bibs? recirc return into cold water side to prevent stratafication in water maker,filter ahead of drinking water and or take offs after filter and after water softener,boiler water feed would want to be filtered ahead of softener.........must dash. Not to be a downer buh is there some way we could disscuss the pipe sizes as 1/2"=15mm 3/4"=22mm and 1"=28mm just to make it easier on my mind? really i grew up converting L.S.D. into american currentcy and i would also like to bag off the KW's for Btus...you can do the math . One thing is i think of 10,000 btu,s as a per person use on the hot water side of the equasion 5,000 is what you have setteled on...maybe its all this American style living i've bought into over the years...so, lets go over the ideas i mentioned earlier this morning on the potable water supply side ,i think a 1" whole house water filter needs to live ahead of everything except a code required hose bib,this is the reason,the outside hose bib can be used to "flush" impurities in the incomming water and there is very little to be gained from filtering the water to it. the reason i suggest the water is filtered prior to the water softener is that one feature will prolong the life of the more expensive softener and it is relatively easy maintinance in comparison. Your boiler feed water would definitely benifit from filtration if nothing else. one other thing to note is the watersoftener installers like a tank Ahead of the water softener so it has Plenty of water to draw from during its cycling. now to the recirc system of the Domestic Hot water...running it into the Cold water side of the system allows the water to Maintain the entire indirect with Hot water verses stratifing the water at the top of the indirect,thereby giving you a mixed water temp upon call for hot through the cold,while a moot point it does make some difference on the availability of plenty of hot water on hand. it will need a check up stream on the cold,..! oops You would benifit by sizing the recirc pump size to a half an inch verses three quaters(22mm) as the recirc doesnt need to be oversized for any reason....oki now we can disscuss the piping to and from the indirect a bit....on the boiler side...i would like to see you have 1" running to and from the water maker for faster recovery...this will do a little for bringing the standards up a notch in supplying the domestic Hot water maker plenty of BTU's on a call for hot water.

Weezbo

Are you still there?

please tell me something about your low loss header...are there 3/4 taps (22mm) on all the ports?

Jimmy Gillies

John

Please take your details to a M&E consultant, it's worth spending a few quid to get them to look over your installation and revise as required. There are many things on your drawing that are WRONG.
I hope you don't think I'm being disrespectful, as I'm not.
Your drawinging is very good, please tell me what CAD software your are using?

Most M&E consultants have PE insurance, so if after them advicing you, things still go pear shaped, you are covered.
I hope that's some help?
Kind regards.
Jimmy Gillies Scotland.

John Aston

Low loss header

Hi.

The low loss header recommended has two 1¼" connections on the primary side and two 1¼" connections on the secondary side.

John Aston

Thanks for replying, Jimmy

I used CorelDraw 6 to do the drawing. It's not the best program in the world, but I'm used to its idiosyncrasies.

I will get some professional help. I just wanted to get as close to the final design as possible before I take that step.

I was intrigued to learn that there are many things wrong with my design. For my interest, Jimmy, could you kindly let me know, say, two of the biggest errors? Thanks.

Weezbo

ok....lets adress that for a momment...

What benifit would be aquired by Not using one inch in and out of it on the boiler side? then lets look at the "Field" for a momment.......what would be the benifit in having the radiant floors and the rads tied into the header with one temp being driven up to meet a demand past another demand that is being driven downthen back up again.? i am willing to say that it will work buh wouldnt it be better to take the Higher temp demand water off early then the lower temperature demand?

Weezbo

let me ask about the recirc pumps....

say that they cost37 pound ten an six each( Thats just a number out of thin air) what is the rational behind placing so many into the equasion? wouldnt one perhaps be sufficent for the rads and one for the floor???or maybe one for the Lot of the emmitters?