WtW Efficiency gain of lower temp. Load Tank

[buffalobillpatrick]

The path for solar directly heating the DHW tank is running the boiler pump (P1) (but not the boiler itself) and the direct solar pump (P5) with the direct solar valve (V2) open and the three way valve (V1) set to send the flow through the storage tank (40G) back to the direct solar pump.(P5)

That path heats the 40G tank. The DHW would be heated if P2 also runs.

[NiHaoMike]

That's how it's intended. If the solar is hot enough to directly heat the 120 gallon DHW, it will also heat the 40 gallon storage tank. You can, of course, stop once the DHW is up to temp.

If you only want to heat the storage tank, just open the direct solar valve and operate the direct solar pump. The radiant floor pump can be operated at the same time if necessary.

[buffalobillpatrick]

I was wondering, if I can control the output temp. of HP Condenser by controlling its water flow?

If I put 2 low head pumps in series, run only 1 for hotter water (1/2 volume) out OR run both for lower temp (full volume).

[NiHaoMike]

That might work, but you'll do better with a variable speed pump or just leave the heat pump running longer. You can also use a servo operated valve.

[buffalobillpatrick]

http://www.groundmed.eu/uploads/medi...l_model_01.pdf

Internal refers to condenser side, external refers to evaporator side.

Figure 5.1 shows how the heating and cooling capacity of the heat pump varies with changes in the internal and external pump frequencies. With respects to the heating capacity, when the flow-rate of water is increased through the condenser (internal pump), it results in an increased heat transfer co-efficient on the water side, resulting in an increase in the condenser U value. This leads to a decrease in the mean temperature difference across the condenser and a reduction in condenser saturation temperature. This results in a lowered condenser saturation pressure, which in turn leads to an increased condensing effect and associated heating capacity. The refrigerant mass flow-rate through the condenser is not significantly affected by the lowered condenser saturation pressure. Therefore, there is little effect on the heating capacity of the system with increasing secondary fluid flow-rates through the condenser. An increase in mass flow-rate of water through the evaporator (external pump) causes an increase in the value of the heat transfer co-efficient on the water side. This results in an increased mass flow-rate of refrigerant which lends to increased heating capacity of the heat pump. With increased mass flow-rate on the secondary side of the evaporator and an increases mass flow-rate of refrigerant through the compressor. This results in an increased heating capacity when compared to varying the internal pump frequency. The effect of varying the pump frequencies on the COP of the system (in heating mode) is shown in Figure 5.2. It can be seen that the maximum COPsys exists at a combination of intermediate frequencies on the internal and external pumps. This is caused by a trade-off between an increase in the heating capacity and power consumption with increased pump frequency.

[buffalobillpatrick]

"servo operated valve" as in EEV?

[NiHaoMike]

More like a globe valve with a servo motor attached to it. Or keep it simple and just run it for a longer time.

[jeff5may]

Don't forget about the solar array. With a 2 ton heat pump drawing all of its heat from the solar source, that 1000 gallon tank may cool down rather fast on chilly overcast days. Water holds lots of heat, but a 2 ton unit could deplete that tank if your heating demands are high. Then you would have no other choice but to use the boiler for a heat source forever, until it got sunny for many hours.

[buffalobillpatrick]

http://ecorenovator.org/forum/attach...1&d=1397593506

Check valves in Main loop elemonate need for loop pump.

Critique please.

[NiHaoMike]

You'll want to add a valve in the solar direct connection to prevent stray flow. I would also have the heat pump draw off the line returning from the heated floors where it would presumably be the coolest.

If you do use two pumps for the heat pump, you'll do better putting one in the main loop so it can also be used to help overcome restriction for direct solar mode.

Also, if the balance point at 90-100F condensing is 35F evaporating, the balance point for 120-130F condensing would be way below 90F evaporating, maybe 50-60F evaporating. And how would you handle the corner case where both zones are calling but the source temperature is between the two balance points?

I still recommend going by my design, albeit probably with a number of modifications. It more or less tries to directly couple the heat pump to the heated floors, with the boiler as a backup. Note that the heat exchanger for the DHW works both ways. Therefore, it's possible to use the DHW tank as reserve for heated floors before the boiler has to activate. When using either the boiler or DHW tank for space heating, it goes directly to the zones without wasting any on the TA. Then once the solar tank goes back above the balance point, the heat pump can start back up. (That situation can occur if the solar tank drops below the balance point at night, then the sun comes up in the morning and heats it up.)

Of which, exactly how are the solar panels/collectors coupled to the solar tank? If possible, it should be designed so that the heat be directly used (if needed) rather than stored.