Hi, I have a problem that I think some of you guys could help me with. I'm a member of a cricket club and our oil fired boiler has died. We are trying to gauge what sized boiler we would need to replace it, our main requirement is to be able to simultaneously supply 4 shower heads plus a little domestic hot water for the kitchen.
Currently we have problems because we have what looks like a domestic sized hot water storage cylinder but also have a monsoon pump feeding the showers so the hot water lasts about 5 minutes, I have been thinking of a combi boiler but have no idea on what sort of flow rate we should be looking at,
14 litres/minute @ 35C doesn't mean a great deal to me in terms of what that would mean to 4 guys standing under a shower.
You might consider a manifold series of tankless water heaters. Look at the different companies that offer tankless water heaters; also talk to plumbing warehouses in your area. Talk to your local plumbing inspector regarding code requirements in the area.
The answer to your question on the showers, a showerhead on average produces
2.5 gallons per minute or less. So 4 showers = 10 gallons per minute
Are the showers used constantly, or in bursts? If used constantly, you must ensure you have enough power to actually instantaneously heat the water. If it is in bursts, then a suitably large storage system may be indicated.
For continuous use, I'd suggest something like a DPS BoilerMaster coupled with a suitably large oil boiler. The BoilerMaster is basically a plate heat exchanger and thermostatic valve that you connect to the boiler's heating circuit like a radiator. It is rated to heat up to 100kW of mains pressure water, if your boiler output can go that high. This system would essentially operate like a huge combi boiler. For 8 litres per minute for each shower, you would need around 20kW each, or 80kW. So a 80kW oil boiler would provide enough to run four reasonable showers continuously. You would need to ensure that the boiler was a modulating type, as otherwise the boiler thermostat will cycle, leading to the showers fluctuating wildly in temperature.
If the usage is bursty, and you would prefer a smaller boiler with a storage system, I might suggest something like a DPS Pandora. These are available up to 250 litres, which would give much longer run times than your current system. They will support flow rates up to around 40 litres per minute, which will run your showers no problem. However, even with a small boiler running simulataneously, the run times for this will only be about 15 minutes, depending on the flow rate.
For larger installations, heatbanks are available with multiple heat exchangers claiming to support up to 15 showers and 450 litres, which would give superlative performance.
All the solutions above use mains pressure water to the showerhead, which is more efficient at cleaning the mud off than a traditional gravity system that you may already have. It also means that no cold water storage is required.
Just as importantly, both solutions use thermostatic mixing valves. You can set these to 43C, which gives a nice hot shower, but prevents people from scalding themselves. The internal water storage (if applicable) is still at
75C, so much more energy is stored compared to a system that uses lower storage temperatures.
Another solution is to use an unvented cylinder. However, heat banks have certain advantages, such as inherently greater safety, and resistance to biological infection, such as leggionaires' disease.
Hi Christian, Many thanks for a comprehensive reply I'll have to study it in some detail. The normal usage will tend to be a maximum of 13 or so players all wanting to have a shower at the end of a game, I guess theoretically there could be
22 of them wanting a shower but unlikely and not everyone especially if we have juniors playing will want a shower. So we could be looking for about
500 litres of hot water over about a 30 minute period not a great demand but enough to upset whoever is in the shower when the hot water runs out. So we could put in a couple of big storage cylinders but I would imagine it would take quite some time to heat up such a large mass of cold water and it could be very wasteful if it isn't all used. Tricky stuff this heating business :-)
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