ASHP Pipe sizing

[Barnboy]

I've looked up 3 different makes of heat pumps that fit the size I'll be looking at fitting and their respective flow rate requirements. 

 

Mitsi 6-17 ltrs/min

Vaillant 6.6-14.3 ltrs/min

Samsung 7-48 ltrs/min

 

I can only get Alpex piping in 32mm external/26mm internal or 40mm external / 33mm internal locally.

The Alpex catalogue says that heatimg distribution pipes should flow up to 0.5m/s and riser and basement pipes 1.0m/s, giving the 32mm a flow rate of 16.2-31.8ltrs per minute and the 40mm a rate of 25.8- 52.8mlltrs per minute.

I need a run of approximately 18mtrs each way from my ASHP to the hot wather tank and UFH manifold but this needs to rise about 4mtrs out of the ASHP into the ceiling joists before a straight run and a drop back down of about 2mtrs, and visa versa on the return leg.

I'm thinking that I will probably need to put an air bleed point on both pipes at the top of the rise out of the ASHP which will involve adding a T into the run and thus creating some resistance. 

So, the big question is, which size pipe do I go for and do I need the air bleed point ? 

The 32/26mm looks capable but will the rise and possible restriction of a T cause an issue ? 

Thanks

 

[JohnMo]

You need to take a step back. Mitsubishi and Vaillant looks like it maybe 6kW flow rates, the other numbers are nonsense. The numbers you are looking are the extreme the pump can flow not the target flow rate. The important number is the target flow rate and max pressure rise to achieve that flow. You need to look at the pump curve and where you need to be on it.

 

For those flow rates in most likelihood you will need 28mm.

 

I am flowing around 1m3/h (16.6l/min), the path mine takes is quite convoluted about 12m each way in 28mm in Hep2O and the longest pipe in the UFH is around 110m (16mm pipe), all flowing from the ASHP circulation pump. Plus the same pump also pumps to a single fan coil in 15mm Hep2O another 15m each way in another direction.

 

I would choose something you can get parts for locally, Hep2O is readily available on Sunday morning if you need a bit.

 

Find your target flow rate and the  max pressure drop first. Calculate the pressure drop on the proposed run second, size pipe to be under pressure drop max figure. If you piping goes up 4m and 2 that's a 2m head ride when you calculate.

 

Put a bleed at high points, makes life simple when filling and getting of air. A tee will add little or no resistance, Hep2O is good for this also as the pipe inserts are thin wall steel. Or you can do these sections in copper and use straight connector between Hep2O and copper.

[Barnboy]

I've looked over and over at this, the only ASHP instructions that I can find with a pressure loss graph are for Samsung as attached. Samsung instructions say 14.4ltrs/minute average so over a 24m flow and return, 12m each way run of 26mm internal I calculate a pressure loss of 0.008kpa and for 33mm internal pipe 0.003kpa using an online calculator,  but looking at the Alpex graph it seems to showthe 26mm intetnal at 110pa/m = 0.11kpa/m = 2.64kpa/24m and for the 33mm internal, 30pa/m = 0.03kpa/m = = 0.72kpa/24m?

Trying to workout the vertical section pressure loss I'm looking at 0.433psi per ft of head = 1.407psi/m = 2.814psi for the 2m you say that my 4m up,2m down each way equates to 19.405kpa.

From my reading of the Samsung graph I can only have around 8/10kpa pressure drop, so whichever size pipe I use, the head pressure over kills my pressure drop allowance.

Am I still going wrong somewhere or do I need to add in a 2nd pump, would this have an effect on my loss ?

Edited July 3 by Barnboy
Additions

[JohnMo]

Not sure where you pdi comes from work in imperial or more preferably metric and only metric units.

 

Basically what goes up, must come down, so from head loss perspective they cancel each other out, but you still have the tube they cancel each other out.

 

But don't Samsung use a pump supplied by you - as in it doesn't have a pump in the monobloc. 

 

So proper perspective, this is the pump head loss chart from my manual (with pump inside monobloc unit)

 

So my duty point is 75kPa at 1m³/h.

 

So on your case you have about 20kPa going through the ASHP and another 55kPa for your piping and heating system.

[Barnboy]

10 minutes ago, JohnMo said:

 

So on your case you have about 20kPa going through the ASHP and another 55kPa for your piping and heating 

 

Where do you find these numbers ?

 

Yes I believe the Samsumg requires an external pump, which I'll have to work out which pump fits the scheme at some point too.

 

I'm just baffled by this, I've been trying to work it out for weeks so that I can order the required pipe but I can't make sense of it.

[JohnMo]

28mm Hep2O at your flow rate is 2m head loss for 100m or about 19.5kPa. So 24m would be about 5kPa.

 

Fittings add metres of head loss, a flow through tee adds no additional resistance 

 

[JohnMo]

1 minute ago, Barnboy said:

I'm just baffled by this,

Start with working out your pipe runs. Do pressure drop calculation.

 

If you are connected directly to UFH heating you just need the pressure loss for the longest loop. It should be more onerous than the cylinder coil.

 

Then look at pump curves and get the smallest pump that does the duty.

 

The attached has worked examples

 

Hep2o_Parts_Users_Guide_Australia_2018.pdf

[Barnboy]

I've had another measure and im somwhere between 32 and 36m round trip for pipework.

According to the Alpex catalogue, without allowing for the rise and fall of the pipework I will have a pressure loss of between 4 and 4.5kpa if I go 32/26mm and 0.96 and 1.08kpa in 40/33mm.

The Samsung spec gives flow of 14.5lpm and a pressure loss of 8kpa whilst the Mitsi gives a flow if 14lpm and pressure loss of 18.16kpa ?

I'm hoping for these numbers that the 32/26mm will happily cope.

I can't find info on whether ot not the Mitsi has it's own pump or find anything relating to it's duty cycle if it for have one, so next it will just be down to converting my numbers to head metres and finding a suitable pump.

[Barnboy]

I've now spent hours and hours trying to work this out.

 

I've come to the conclusion that as my circuit from the ashp back to it is a mirror image then where it rises on one leg, it falls back the same amount on the opposite leg so any pressure differences from height will completely cancel each other out.

 

I've looked as deep as I can find for the possible heat pumps that I will choose from, my heat loss at 20⁰c OAT to room temp according to Jeremy's spreadsheet shows 4.2kw so a 5kw unit should be good .

 The target flow rates shown for these are around 14l/m and max pressure drop of 14kpa. I've got a pressure drop of pipe only of the feed and return of 4kpa.

I cant find details of any inbuilt pumps to see any duty cycles.

 

My problem now is that I can't find any pressure drop numbers for any anti freeze valves, ball valves etc.

Does anyone have anything for these ?

 

[JohnMo]

23 minutes ago, Barnboy said:

falls back the same amount on the opposite leg so any pressure differences from height will completely cancel each other out.

Correct 

 

On 03/07/2024 at 21:33, JohnMo said:

Basically what goes up, must come down, so from head loss perspective they cancel each other out

 

25 minutes ago, Barnboy said:

4.2kw so a 5kw unit should be good .

Be careful as different manufacturers label differently. You need to look at the datasheet to make sure it's output is ok at your lowest temperature.

 

Would question your design basis. It's more normal to have -3 outside and 20 to 21 inside except bedroom at 18.

 

You need head room to do hot water. Allow 3 hrs. So working with 4.2kW, 4.2kW x 24hrs, then divide that total by 21 hrs, this should give you the size you need. Replace the 4.2kW with a better design basis.

34 minutes ago, Barnboy said:

anti freeze valves, ball valves etc.

They don't restrict flow so zero.

[Barnboy]

5 hours ago, JohnMo said:

Would question your design basis. It's more normal to have -3 outside and 20 to 21 inside except bedroom at 18.

 

You need head room to do hot water. Allow 3 hrs. So working with 4.2kW, 4.2kW x 24hrs, then divide that total by 21 hrs, this should give you the size you need. Replace the 4.2kW with a better design basis

We don't normally get that cold this far south, the lowest average over the last 30yrs has been 7⁰C but it has been recorded down to -3 at some point during that time too.

My 25⁰ OAT to inside Hest loss is 5.155kw, so x 24/21=5.89kw, do a 6kw unit?

That narrows me to Mitsubishi, the WZ60VAA(BS) unit has the following data,

This looks like it will cover the required output, or is it too much ?

5 hours ago, JohnMo said:

6 hours ago, Barnboy said:

anti freeze valves, ball valves etc.

They don't restrict flow so zero

They must all add up to something? The pipe data that I have for the make of pipe that I can source has zeta valued for their 90⁰, tees, straight couplings etc, they don't add up to very much but added together will give a few kpa ?

[JohnMo]

8 hours ago, Barnboy said:

narrows me to Mitsubishi, the WZ60VAA(BS) unit has the following data,

That looks the right unit from mitsubishi.

 

8 hours ago, Barnboy said:

They must all add up to something?

A ball valve is just like open pipe when open, so no restrictions.

[Barnboy]

5 hours ago, JohnMo said:

A ball valve is just like open pipe when open, so no restrictions

But if a length of pipe has a pressure loss and so do fittings, surely any other unit, motorised valve, ball valve etc must give some pressure loss ?

[JohnMo]

1 hour ago, Barnboy said:

But if a length of pipe has a pressure loss and so do fittings, surely any other unit, motorised valve, ball valve etc must give some pressure loss ?

Ball valve just treat the same as a piece of pipe, if it's 100mm long just add that to the pipe length 

 

Diverter valves are different they have a pressure drop and some can be quite restrictive. Same for strainers and strainer ball valves.

 

Think you maybe overthinking all this, you don't need to detail the last Pa drop in pressure. Aim for a reasonably low pressure drop.

 

No gate valves, just ball valves for isolation, at least a 28mm diverter, a strainer, that's about all you have in the system. Keep everything simple. I would just plump the whole lot in either copper or Hep2O or a mix of the two, where it best suits the run. Copper tails on any compression joints, the transfer to Hep2O with a straight coupler. High points will need a bottle air trap to bleed air, just need a 28 by 15mm tee for that. Low points need a drain. If you want a low pressure drop diverter an ESBE is fine, I just use a Honeywell 28mm it's fine.

[Barnboy]

7 hours ago, JohnMo said:

 

Think you maybe overthinking all this, you don't need to detail the last Pa drop in pressure. Aim for a reasonably low pressure drop.

Story of my life, I overthink everything and then get overtaken by those who just wing it and get away with everything.

 

Mitsi show their spec as a test flow rate of 17.2l/min, which os the top of their flow range,  and pressure differences of 19kpa.

My calculations using h2x software give me 4.95kpa for 32/26mmpipe  and 1.59kpa for 40/33mm pipe @17.2l/min so I should be fine with the 32/26mm ? 40 only comes in 3mtr lengths where as 32 comes in a nice 50m roll, so no joints.

[Barnboy]

31/26mm Roll with 2x tee pieces to allow for air vents cones out complete at 5.15kpa.

 

40/33mm, 5mtr lengths with 2x tee pieces and 4x couplings comes out at 1.96kpa

 

Both calculations are at the 17.2l/min velocity listed in the Ecodan paperwork which allows 19kpa.

These are just the main run, so a little extra to add for motorised valves etc but at 3kpa difference I'm guessing that the 32/26mm should be OK?

[sharpener]

With a delta T of 5 deg a flow of 14litres/min gives you 4.8 kW and 20 gives you 7.2

 

Rule of thumb: 15mm pipe is good for 3kW, 22mm for 6kW, 28mm for 12kW at reasonable flow velocites.

 

Your original 32/26 Alpex should be more than enough for a 7kW-ish HP, do not fret about the fittings overmuch.

[Barnboy]

Thanks @sharpener, hopefully yourself and @JohnMo have set my mind to resttoill just make sure I use as low resistance as possible fittings once I get to where I need to be.

[JohnMo]

8 minutes ago, Barnboy said:

use as low resistance

I have just taken out the glycol on my system and now using VDI2035 (straight water with testing). Without any other changes the water flow rate jumped from 1m³/h to 1.3m³/h. So glycol slows the system right down.

[Dave Jones]

heat capacity of various liquids Vs discosity

 

calculation required 

[sharpener]

Depends on which of several different glycols, and the concentrations thereof. See this thread https://forum.buildhub.org.uk/topic/37452-are-all-glycols-equal/.

 

[Barnboy]

14 hours ago, JohnMo said:

have just taken out the glycol on my system and now using VDI2035 (straight water with testing).

Is that water that you've tested until you've found a suitable source or deionized bottled water ?

[JohnMo]

38 minutes ago, Barnboy said:

Is that water that you've tested until you've found a suitable source or deionized bottled water ?

It tap water going through an Ion Exchange resin in a 10" filter housing.

 

The water that came out was brown and although had glycol it has obviously had picked some corrosion from a carbon steel buffer I had in the system.

 

 

The water circulating is correctly sitting at 168ppm dissolved solids and 341 micro seimens conductivity. pH is about 7.3, but this should move over time to about 8.

 

Have a slip stream through the resin, setup which I am going to run again tomorrow for a few hours, the aim is to get the ppm down below 150.

[Barnboy]

11 hours ago, JohnMo said:

It tap water going through an Ion Exchange resin in a 10" filter housing

What is the Ion exchange unit that you are using ? 

I've had a look about this morning and all the units I can find are quite expensive.

[JohnMo]

17 minutes ago, Barnboy said:

What is the Ion exchange unit that you are using ? 

I've had a look about this morning and all the units I can find are quite expensive.

I found the same so looked at what actually makes up a unit and nothing much.

 

Break down of parts I have used

 

Resin Purolite MB400IND Mixed Bed Indicator DI resin 60/40 1L from Complete Aquatics  - I bought 2L for £32 delivered (only used just under 1L so far and its 50% depleted)

VYAIR 10" Refillable Transparent filter housing (empty for DI resin - £7.99 from Amazon, this holds the resin and goes inside the 10" filter housing

10" transparent filter housing with 3/4" tappings - £20 from Amazon

3/4 male X2 (for filter housing) and 3/4 female X2 (for fill and flush manifold) garden hose tap connectors - Amazon £14

Some off cuts of garden hose and garden hose end connectors

 

Already had a fill and flush manifold in the system.

 

So about £75 all in (plus the fill and flush point) and have enough resin to treat around 2000L of water.

 

All you do is replace the resin when it all changes from blue to brown. So £16 instead of £160 charged for complete cartridge.