General Rad/UFH Questions in conjunction with Heat Pumps

[Jon Glanfield]

Following on from the General Heat Pump questions I thought a thread on heat emitters might be worthwhile so here goes:

Radiators

Are people happy to use radiators, provided they are sized correctly, what is the highest design flow temp people are confident to work with?

If you do opt to use radiators what are people's opinions on low water content versions which provide a lower mass and quicker response time versus regular panels or old style cast, which provide a larger thermal mass for the heat pump to work with which would make more sense from an efficiency point of view.

Usually the LWC versions are fan coils but generally the cost seems to be prohibitive for projects we have looked at.

UFH Flow Temps and Timber

There seems to be a difference of opinion in the UK about what flow temps are required when working with a suspended timber floor. In our experience this has ranged from 35 degrees to 60 degrees and although it relies to a degree on the type of pipe (see below), diffusion system (see below) and centres what real life experience does everyone have?

We have worked with UFH designers who claim that PEX at 200 centres on plate with a chip floor a HP will still achieve the usual 18 degrees required on the first floor and having followed their advice we have not had any complaints (but this does not mean the system is optimised), however others will not sanction this.

Does anyone blend temps on UFH systems with HP's and if so how, the crude injection blending valves don't work well enough with WC flow temps and 3-way mixers don't always wire to all HP's.

First Floor Solutions

In conjuction with the above comments I personally don't like plates (HPs are not designed for the quick response times and quick heat drops that plate create), but the structural integrity of the joists may not permit a biscuit mix or pug screed, is a mixed system a better option in this case or others finding plate based systems are fine?

Also we work on the basis that on a screed a serpentine pattern is the best option for even heat transfer, lower static losses, and less risk of damage to pipework, but this is not feasible on a first floor, so do others just accept the limitations of a bay to bay U-shaped layout if there is no other option?

Pipework

We use suppliers that have PEX and Alupex products. Are there still issues with Alupex or are the delamination and loss of barrier a legend that was? We have also sourced data that suggests that PB has low emissivity rates in comparison with PEX and Alupex and has such have steered clear of it, but it's flexibility is a benefit when working with tight centres

We have not used PERT yet, does anyone have any experience of it and how does it compare with say Alupex that appears to have higer emission rates than other pipe?

Are there any other products that we should be researching that perform better, with the tighter centres required of HP applications.

Centres/Delta T's/Output

UK based designers of UFH seem to still work on high delta t's, which doesn't always present a major issue because MWT is often similar, but it does mean that flow rates in the design and commissioning paperwork is moribund, meaning more time on site fettling.

Also we find a diversity of approach as regards centres and watts per metre throughput and often we have to request tighter centres. Even a major supplier of HP's with an UFH designer and retailer under its wing makes some dubious claims and their MD is also tech chair of the UHMA (Underfloor Heating Manufacturers Association), they work on the basis of 100 watts per sqm from a heat pump driven system out of screed even using 200 centres, what therefore are peoples views on centres, flow temps and watts per sqm by floor covering and substrate?

[MikeHolm]

Nice post.

I will say that I learned my trade from Germans and at the time, high mass was the way to go, both in boilers and rads so, while I have forsaken the cast boilers for the condensing Vitodens types, I will not forsake the cast rads. I believe they are the next best thing to a good thick cement floor. Of course, I have a good number of old ones available to me, cheap, so that helps.

The standard spacing for 1/2" tubing in North America is 200-225mm in screed such as gypsum cement which is most often 30-35mm thick and 300mm in slab concrete which is 75-100mm thick (not suspended floors). If you mean Oriented strand board for chip board, we will not use it on floors as it will not last long term (only the cheap tract house builders use it) Plywood all the way.
I have always tried to get people to put in more mass and use the slab as a heat dump.
I have always hated plates and for the temps needed, it is better to go with rads.

I would like to see a pic of your serpentine vs U shapes. We may not use the same language for describing the layouts.

I have tried the Pex/Al/Pex in floors but don't like it, I prefer Rehau but for mains leasing to the manifolds, it is fine. I have noted in systems that are 10 years old, for example, that composite pipes that we get here must promote O2 migration to the system components. I have replaced pumps that have been plugged with corrosion and i have not been able to find another reason for it. This is in system which have a high degree of composite pipe outside the slab as O2 migration is far slower in a slab.

Don't know what PERT is???

I am leaning towards more more pipe on the floor than less, even with 80m loop lengths, which are standard here (75m actually). What do you mean by "fettling"? I've never heard the term before.

[frank]

The plumber I work with always lays the UF loops at 100mm centres around any external walls for the first 3 loops then drops back to a maximum of 150mm for the rest of the room. His thinking is that the additional cost of the piping far outweighs any complaints that follow, due to non performance, and, as he says, once it's down, you can't increase it but you can turn the stat down!

I was called out to a problem site just before Christmas where the end user was complaining that the house was not getting up to temp during the recent cold spell in the UK (-15 - 18C)

Turned out that the UFH was designed for -3C lowest with a room at 21C.

I pointed out that system was installed as designed and suggested that he needed additional heating during times where the ambient dropped below design (-3C) but he was not happy at the solution offered - dig up the UFH and re-lay with closer centres.

[Bigfreeze]

Jon Glanfield;224054]Following on from the General Heat Pump questions I thought a thread on heat emitters might be worthwhile so here goes:

Radiators

Are people happy to use radiators, provided they are sized correctly, what is the highest design flow temp people are confident to work with?

If you do opt to use radiators what are people's opinions on low water content versions which provide a lower mass and quicker response time versus regular panels or old style cast, which provide a larger thermal mass for the heat pump to work with which would make more sense from an efficiency point of view.

Usually the LWC versions are fan coils but generally the cost seems to be prohibitive for projects we have looked at.

Generally you couldn't class any radiator system as having thermal mass. They will cool down quickly regardless. Because you should be running with a buffer I would not have a preference for one over the other. The temp they require is the main issue. Generally i would not push a HP over 40C on the heating cycle. Beyond that I don't think the system is suitable to a heat pump

UFH Flow Temps and Timber

There seems to be a difference of opinion in the UK about what flow temps are required when working with a suspended timber floor. In our experience this has ranged from 35 degrees to 60 degrees and although it relies to a degree on the type of pipe (see below), diffusion system (see below) and centres what real life experience does everyone have?

Once again if running a system like this there is no heat retention. I really try to avoid the situation at all costs. It can be impossible to predict the outcome. Floors should be in contact with the screed. You never know what draughts will circulate in the void in a suspended floor that will influence your outcome

We have worked with UFH designers who claim that PEX at 200 centres on plate with a chip floor a HP will still achieve the usual 18 degrees required on the first floor and having followed their advice we have not had any complaints (but this does not mean the system is optimised), however others will not sanction this.

Does anyone blend temps on UFH systems with HP's and if so how, the crude injection blending valves don't work well enough with WC flow temps and 3-way mixers don't always wire to all HP's.

First Floor Solutions

In conjuction with the above comments I personally don't like plates (HPs are not designed for the quick response times and quick heat drops that plate create), but the structural integrity of the joists may not permit a biscuit mix or pug screed, is a mixed system a better option in this case or others finding plate based systems are fine?

Most floor should easily take a low level antracite screed if concrete screed is not an option. You could also look to wall heating

Also we work on the basis that on a screed a serpentine pattern is the best option for even heat transfer, lower static losses, and less risk of damage to pipework, but this is not feasible on a first floor, so do others just accept the limitations of a bay to bay U-shaped layout if there is no other option?

Pipework

We use suppliers that have PEX and Alupex products. Are there still issues with Alupex or are the delamination and loss of barrier a legend that was? We have also sourced data that suggests that PB has low emissivity rates in comparison with PEX and Alupex and has such have steered clear of it, but it's flexibility is a benefit when working with tight centres

We have not used PERT yet, does anyone have any experience of it and how does it compare with say Alupex that appears to have higer emission rates than other pipe?

Are there any other products that we should be researching that perform better, with the tighter centres required of HP applications.

We've worked with PB for years. Fantastic pipe but the quality stuff can be expensive. PERT is slightly more flexible than PEXc and I would prefer it. Alupex is a gimmick when it comes to UFH. Far more suited to plumbing applications

Centres/Delta T's/Output

UK based designers of UFH seem to still work on high delta t's, which doesn't always present a major issue because MWT is often similar, but it does mean that flow rates in the design and commissioning paperwork is moribund, meaning more time on site fettling.

Also we find a diversity of approach as regards centres and watts per metre throughput and often we have to request tighter centres. Even a major supplier of HP's with an UFH designer and retailer under its wing makes some dubious claims and their MD is also tech chair of the UHMA (Underfloor Heating Manufacturers Association), they work on the basis of 100 watts per sqm from a heat pump driven system out of screed even using 200 centres, what therefore are peoples views on centres, flow temps and watts per sqm by floor covering and substrate?

As here the design available is crap and not geared towards HPs at all. We work on 100mm centers and loops of 80m max, its a 15mm pipe with the same bore as 16mm. We aim for a 5C differential across the floor. Our supplier reckons at 30c that will give us 65w per sqm. 100W as you were quoted is ridiculous. If you went to 18mm you would get the same performance at 120mm. We aim to be below 30C as much as possible. Sometimes the level of insulation in a house won't allow this. Sometimes we better it considerably.

[MikeHolm]

What is PERT please?

[Jon Glanfield]

Hi Mike, it's another multi layer pipe this is from an UFH supplier who uses it:

"The flexible 5 layer polyethylene PE-RT pipe is a "midi composite" pipe with a 50 year guarantee and is CE approved. The oygen barrier is located within the centre of the pipe and is 5 times greater than the requirement under DIN4726. The 5 layer design permanently prevents the damaging effects of ambient moisture on the diffusion barrier layer. Whats more the outer PE-RT layer offers protection against possible damage to the EVOH layer during transport and installation.

PE-RT polyethylene pipe is extremely strong, highly flexible and is both heat and age-resistant. It has been tested to withstand continuous pressure of 14.1bar at 60C for 100 years.

Pipe is availble in a range of sizes: 75m's,90m's,105m's,125m's,250m's & 750m's."

We have not used it but IHS (Invisible Heating Systems) use/sell it and sing its praises.

By serpentine I mean a bit like a snail or a coil, where you work around the room into the centre and then out again.

Jon

[Bigfreeze]

PolyEthylene Resitant Temperature. Extemely strong, it is, extremely flexible, it isn't. Its averagely flexible but a very good pipe for ufh none the less.

[MikeHolm]

Is it pricey, compared to something like Raupex or uponor Pepex. I am wondering if it could be a replacement for the "less than ideal" pex/al/pex we get here.

[heat pump ac]

I am trying to establish which type of under floor heating pipe is the best to use, from what i see on this thread we are looking at either PB or PERT. Does anyone have any data or a calculation methods for these pipes which will allow calculation of outputs at varying pipe centres and mean flow temps? I want to be able to design our own systems rather than relay on expensive companies who take on the design and then want no responsibility after the sale is complete.

[MikeHolm]

IF you want to go PEX, and I see no reason not to, the best ones IMO are REHAU followed by (what was Wirsbo) Uponor. I've go at least 1,000,000 ft of the stuff installed over the years and I'm quite satisfied with it. These two far outweigh any other straight PEX tubings. Composite pipes are a different matter but might be more expensive.

Other than the ability to hold a bend, which is useful for mains piping, I don't see much advantage of anything over Rehau...in the floor. Outside the screed or concrete, O2 barrier is really important and I took a long time finding the one with the least O2 migration. You guys across the pond have a much better selection to choose from than we do.

[frank]

Does anyone have any data or a calculation methods for these pipes which will allow calculation of outputs at varying pipe centres and mean flow temps? I want to be able to design our own systems rather than relay on expensive companies who take on the design and then want no responsibility after the sale is complete.

Have a look on here and then click on the Featured Download link on the Left Hand side. Scroll down to the pipe sizing page near the bottom.
http://www.ufch.com/

[Jon Glanfield]

Does anyone have a view on optimum layouts for UFH, there appear to be differing views as usual, but we are finding that when working at 100mm centres a snail layout seems to be the easiest to avoid multiple tight bends at each end of the more normal up and down loops. I have also heard that this provides a more even distribution into the screed and I would expect that the static losses would be lower with slower bends.

Also what sort of gap do people leave between pipework and walls, again there are different views, but I wouldn't have thought a stud wall would absorb much and a stone/brick wall would just increase the spread of heat slightly.

Mike, sorry I forgot to explain "fettling" is a highly technical term, I am surprised with your evident experience you have not come across it before.............it's northern (England) for adjusting things.

Jon

[MikeHolm]

Hi Jon,

We normally leave 150mm from any wall just because some careless carpenter might decide to nail gun a tube while putting down baseboard ( I guess you call it skirting?). Nobody steps that close to the wall anyway.

all the manuals I have ever seen promote the laying of the feed and return beside each other for best heat distribution but most people I know do a serpentine (the germans call it meander) because it is easier and they work from the outside walls inward, feed to return. I have done it both ways many times and I've done some temperature measurements and while there is a difference, it is usually not to great as to get comments from the homeowner. Regardless of which way it is done I hate those really tight 180 deg bends and avoid them as much as possible.

What you really want is to keep the homeowner from doing any "fettling" with the controls.