rad and pipe sizing for air to water heat source

[Jimbob]

hi all,

looking at installing an air to water heat source pump and a new central heating system in a property. Now according to worcester-bosch website the rad's will require upsizing 20-30%, i assume to allow for the lower temps running through the rads.

But a friend said he spoke to the rep, and was told that the flow and return pipework needed upsizing 50% and not the radiators? I cant understand why this would need this? any ideas?

thanks in advance

 

[migoplumber]

im not familiar with the system, however it makes sense that if you need more heat output from a radiator, and you have a lower input temperature, then increasing the rad size would compensate for that.

as for the pipe sizing, if you have to increase the radiator sizes, then it also makes sense to increase pipe sizes to cope with the extra water in the system...
that said however you only need to make the water flow through the pipes at a desired set speed 1.5m/s is perfect. you may be able to achieve this by using a variable speed circulating pump instead of changing your pipework.

if this is your job for a client, cover your back well on costs, explain all in black and white, including the possibility of extras!

if it where my job, i would not make any changes to the interior instalation except maybe upgrade the size of rads according to the calculation charts worchester bosch can provide you with.

most houses are over sized anyway, and a radiator with 300kcals more or less wouldnt be noticed.

good luck
shaun

 

[unguided1]

Hi jimbob
I have installed several heating systems using ASHPs now, and instead of using steel rads I have used smiths ecovectors you could also look at Jaga's as well. the actual design on how the rads work is old technology, much the same as skirting heating but it is all being marketed as microgeneration now.
If you are intending to stick with steel rads, then yes over size the rads according to the manufacturers recomendations.
Most ASHP's Have inch and a quarter stabbings I usually bush these down to one inch,
What are you intending to install for doing the hot water, because I can recommend an air source hot water cylinder that is a cracking piece of kit.
regards
Mike

 

[Jimbob]

Well after speaking with a rep today i found out the flow sizes do not need to be increased anymore than normal but obviously you have got to allow for larger rads, although i mainly use a rule of thumb method in such a small place. I am actually working for a builder who is doing it in one of his own places so im just changing things as problem arise but he seems to think he knows everything... which he doesnt really. But then iv never had any experiance with them.

That actually leads me too my next question unguided1... the guy has supplyed me with a 300 litre unvented twin coil system to connect too... but you said about a specific air source hot water cylinder? would a normal unvented cylinder be ok with it because the guy is trying to use this instead of a worcester bosch cylinder to save money.

The rep also said about using a buffer... which id presume is a form of heatstore? which we dont plan on usig in the system, so he said i could keep the heating system an open circulting system and just use TRV's on bedrooms so a buffer wouldnt be required? i can see this job being a pain.

If it were one of my jobs i would of recommended underfloor heating due too the running temps of the 'ASHP' but nevermind.

ta

 

[unguided1]

Hi Jimbob
I have to answer this very carefully as I do not know all the facts about the system you are installing or the type of cylinder, and with out knowing all the specifics I could end up miss informing you.
I assume that by going with a twin coil cylinder you are intending to use another heat source, possibly solar.
I would say that each system is worked out on its own merits, no two systems are the same, If your customer has been advised on what he needs, and then changes it to suit his budget you may find yourself running into difficulties later

Me personally I would not use steel radiators, and for heating the domestic hot water I would use an ecocent hot water cylinder, these can also be used in conjunction with solar
regards
mike

 

[Jimbob]

Ok i can see why you would be better using aluminium rads. But the rep did say about upsizing the rads 35% to allow for the lower tempertures, which in theory should compensate. My main concern really is using a normal unvented cylinder. Sorry Iv had no experience when it comes to ASHP, so what difference would a ecocent have over a standard cylinder? I believe the primary coil in the DHW cylinder is rated to 20KW. Iv not even recieved any technical literture on the heat pump yet, all i know is that it is a worcester-bosch.

Your correct in saying the secondary coil is for solar.

cheers, James

 

[unguided1]

Hi jimbob
the advantage of the ecocent over a normal unvented cylinder is you will not have to heat the ecocent with the worcester ASHP, this one has its own ASHP attached to the top of the cylinder and it ducts any waste warm air from a loft space through the machine to outside only using 810 watts of electricity, and with the solar coil being used it will cost virtually nothing to run. this means that the your worcester ASHP can be just used for the heating.
Regards
Mike

 

[Jimbob]

ok well the heat pump turned up but it also came with a cylinder to our surprise. And it was bigger so i had to move it into the kitchen, and left with a redundant cylinder. Seems a very swish bit of kit and only took a day to install (although i was flat out). The rads are huge (35% huger to be exact). Also the supplied hot water unit doesnt have any accomadation for solar! So have to fit them elsewhere now.

going to comission it on monday after electrician has been so will be intresting to see how it operates.

 

[unguided1]

Hi jimbob
good luck with it all and if possible let us know how you get on, I have already sent you a private message with my number any prolems give us a call.
Regards
mike