GS heat pump control sys

[hairyben]

How is a ground source heating sys "controlled"?

System is mixed, low temp underfloor piping on ground floor with a 8 way manifold and convector radiators upstairs with inline wax valves. A multizone heatmiser system will control it all via about 16 individual room stats.

Now conventional heating controls "demand" heat by opening a valve and getting an instant high temperature supply. I was of the understanding the ground source system runs continually and increases workload to increase temp, thus a conventional system of valves opening and closing would be no good. A plumbing firm are doing the heating sys and a home automation firm are doing the controls, and the plumber on the job is worried.

I might be wrong, but if I'm correct there's going to be huge issue, and although its "not my problem" I might get quizzed on it.

 

[Biggles..]

The GSHP works by weather compensation and the internal software,curves and pipestats with in the unit determine pump running time and aux heating.

If you've got individually zoned rooms you'll struggle to get it to work the solution normally used is to install a buffer tank.GSHP warms the buffer which will run the GSHP at its max efficency with out the aux being needed.

The heating will then be driven off of the buffer, this enables complete zoning to be achieved because the GSHP unit isnt actually concerned with any room temp other than the one its located in.

Normal GSHP with out buffer see an open loop heating system purely controlled by the WC curve.

Most units produce about 40degC due to the refridge they use some companies are now producing 65deg running units.With the lower temps,most UFH companies will not design or guarentee(they like 45 and above),rads should be 20% oversized and always open loop.

 

[hairyben]

Thanks. That makes sense, so the zones have an on-demand hot supply. I'm pretty sure there's no buffer tank, unless the megaflow-type HW cylinder can perform double duty?

What kinda size is the buffer tank BTW? Decent sized house, 5 bed, 4 receps, conservatory and bad heat loss through single glaze lead windows.

No plans to install it myself, I'm a spark, I just want to give the customer some reassurance and kind of idea what needs to be done when it hits the fan and everyone else shugs and flaps. I don't try to look clever, it just comes easily with some of the pillocks in the building game.

 

[Dick Puller]

Ben, there's a few skools of thought regarding UFH & GSHP, many, including myself, view that the use of buffer tanks is pointless. We believe in firing the heat directly into the floor & only have the minimum controls, with outside & flow temperature stats/thermisters controling the whole system.

Lots of Greenwash salesmen/con men have jumped on the band wagon, and will try to sell you anything!!!

Granted with your first floor heating, your case is a bit differant, but unused areas like that will not require heating during the day or overnight. But that can be controlled by a set-back stat, easy really.

Always ask a time-served Plumber & Heating Engineer, they have no sales targets to meet!!!

 

[hairyben]

Ben, there's a few skools of thought regarding UFH & GSHP, many, including myself, view that the use of buffer tanks is pointless. We believe in firing the heat directly into the floor & only have the minimum controls, with outside & flow temperature stats/thermisters controling the whole system.

Lots of Greenwash salesmen/con men have jumped on the band wagon, and will try to sell you anything!!!

Granted with your first floor heating, your case is a bit differant, but unused areas like that will not require heating during the day or overnight. But that can be controlled by a set-back stat, easy really.

Always ask a time-served Plumber & Heating Engineer, they have no sales targets to meet!!!

Unfortunately the multi-zone web-interface oh-la-la control system is now installed and the client will go bananas if told it's useless. What I want to know are the fix-options. The house is quite complex in that it encompasses low loss interior rooms through to a conservatory so heat demand will be unequal.

And you're totally right on the engineers advice, unfortunately heat pumps are still a bit of a novelty for the well-heeled and the whole so-fashionable green angle means there's probably more chancers than decent experienced engineers in the game. The first company were sacked off the job for being a shower (no experience of refurb work, only simple to-the-plan installs on formulaic new builds)

 

[Dick Puller]

The house is quite complex in that it encompasses low loss interior rooms through to a conservatory so heat demand will be unequal...............................Another big selling point by UFH sales/con men is controls. Your project/home(?), of course, has rooms with various heat-loss & heat requirements, in fact the only thing that'll not vary is the time the floor takes to heat up & cool down, so unless you have thermostats in each room with floor sensors, they're a complete waste of time & MONEY!!! Too many controls on UFH is pointless, the floors don't react quick enough & standard room stats are calibrated to a 5 deg + or -.
So you can have one room with an ambient temperature at 26* & an ajoining room at 16*!!!

Think also about your GSHP, pumping out 40-50*(tops) water temperature, you are very limited in what you can do with water that temperature & I hope your UFH cowboys have done their design work correct, cause at that low a mean water flow temperature - 200mm pipe centres is going to be farting at thunder in some areas!!

 

[doitall]

A lot Of what Dick Puller says makes sense, (for a change)

40-50 is considered low for a gshp, 50-65 being the target area, but that is down to the installer and equipment, slinkies for example will freeze the ground if you try to get that temperature.

Buffer tanks in my opinion are essential, and helps to level the highs and lows, with any heat pump you don't want them stopping and starting, and a buffer tanks helps prevent that.

At the end of the day, they either know what they are doing or it don't work very well.

 

[hairyben]

Heh, I'm totally with you, simplicity is normally best. Most customers prefer a 24hr mechanical timeclock with boost/adv controls when you point out it's simple to adjust vs. finding/reading/understanding the instructions and ask them if they really need 7 day functionality- most don't, when they think about it.

But the home automation guy thats flogged him the heatmiser is the opposite, complexity for the sake of it, and almost needed restraining from trying to flog the customer smart lighting etc etc that he wasn't interested in... so now we have multi zones and I think the challenge thats going to be faced is making it work, not what should have been done instead.

which, as far as I can see with my limited knowledge, does bring us back to the buffer tank idea.

 

[Dick Puller]

with any heat pump you don't want them stopping and starting........................Very true, but you're not going to get it working on cheap rate leccy at optimum times anyway. So you decide on the comfort & set back times that suit your requirements. Buffer tank or no buffer tank, when that property is up to temperature, the GSHP will only be ticking over anyway, so why fit a buffer tank?? There's no point!!

 

[Dick Puller]

Seen 100's of UFH systems with individual room stats that never go on or off. A complete waste of money, like a buffer tank with a GSHP.

 

[doitall]

When it's ticking over is when you do need a buffer tank, unless you factor in a 10 deg start/stop differential.

 

[simond]

The buffer tank is needed to ensure that the 'degree minute' running times are suitable to achieve maximum CoP and longevity of the compressor.

The latest inverter driven compressors are less critical of buffering, but any heat pump will work more efficiently with a steady load, such as a large thermal mass. Turning off zones intermittently will perversely be likely to reduce efficiency.

 

[Dick Puller]

Any heating appliance works at it's optimum when there's a high demand.

But a GSHP will not work at it's optimum when the cheap leccy is available. So there's no way you will get the published COP for these units anyway, unless you are running it on expensive standard tariff.
Oh yes, it's running at it's optimum on E7 tariff at 2.00am??!!!
Get real!!!...............................Far too much mis-selling going on with these greenwash products!!

 

[Dick Puller]

You'll be trying to tell me next that ASHPs are cheap!! All these HPs are very expensive to buy & for a limited saving on running costs, it takes years for pay-back!!

Far, far better to put loads of solar panels on your roof.

 

[doitall]

Why ever not Dp, if installed correctly, the collector loops will harvest a constant 12c day or night.

An E10 meter will reduce daytime running costs.

As above a COP of 5-1 is sustainable if sized to fit the property.

Mis-selling ??? without a doubt you are 100% correct, you only need to go to the trade shows to see that.